New experiments physico-mechanical, touching the air — New experiments physico-mechanical, touching the spring of the air, and its effects

New experiments physico-mechanical, touching the air — New experiments physico-mechanical, touching the spring of the air, and its effects

Table of contents

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Title page

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EXPERIMENT I.

EXPERIMENT II.

EXPERIMENT III.

EXPERIMENT IV.

EXPERIMENT V.

EXPERIMENT VI.

EXPERIMENT VII.

EXPERIMENT VIII.

EXPERIMENT IX.

EXPERIMENT X.

EXPERIMENT XI.

EXPERIMENT XII.

EXPERIMENT XIII.

EXPERIMENT XIV.

EXPERIMENT XV.

EXPERIMENT XVI.

EXPERIMENT XVII.

EXPERIMENT XVIII.

EXPERIMENT XIX.

EXPERIMENT XX.

EXPERIMENT XXI.

EXPERIMENT XXII.

EXPERIMENT XXIII.

EXPERIMENT XXIV.

EXPERIMENT XXV.

EXPERIMENT XXVI.

EXPERIMENT XXVII.

EXPERIMENT XXVIII.

EXPERIMENT XXIX.

EXPERIMENT XXX.

EXPERIMENT XXXI.

EXPERIMENT XXXII.

EXPERIMENT XXXIII.

EXPERIMENT XXXIIII.

EXPERIMENT XXXV.

EXPERIMENT XXXVI.

EXPERIMENT XXXVII.

EXPERIMENT XXXVIII.

EXPERIMENT XXXIX.

EXPERIMENT XL.

EXPERIMENT XLI.

A Digression containing some Doubts touching Respiration.

EXPERIMENT XLII.

EXPERIMENT XLIII.

The CONCLVSION.

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Title page

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THE AUTHOUR's PREFACE AND DECLARATION.

A DEFENCE Of Mr. R. BOYLE's EXPLICATIONS of his Physico-Mechanical EXPERIMENTS, against FRANCISCUS LINUS.

The I. Part. Wherein the Adversaries Objections against the Elaterists are examined.

CHAP. I.

CHAP. II.

CHAP. III.

CHAP. IV.

CHAP. V.

CHAP. VI.

The II. Part. Wherein the Adversaries Funicular Hypothesis is examin'd

CHAP. I. What is alledged to prove the Funiculus is consider'd; and some Difficulties are propos'd against the Hypothesis.

CHAP. II Divers other Difficulties are objected against the Funicular Hypothesis

CHAP. III. The Aristotelean Rarefaction (proposed by the Adversary) examin'd.

CHAP. IV. A Consideration (pertinent to the present Controversie) of what happens in trying the Torricellian and other Experiments, at the tops and feet of Hills.

CHAP. V. Two new Experiments touching the measure of the Force of the Spring of Air compress'd and dilated.

The III. Part. Wherein what is objected against Mr. Boyle's Explications of particular Experiments, is answered.

A defence of our 1. and 2. Experiments.

The 3. Experiment.

The 4. Experiment.

The 5. Experiment.

The 8. Experiment.

The 9. Experiment.

The 17 Experiment defended.

The 18 Experiment.

The 19 Experiment.

The 20 Experiment.

The 31 Experiment.

The 32 and 33 Experiments.

The 34, 35 and 36 Experiments.

The 37 Experiment.

The 38 and 39 Experiments.

The 40 and 41 Experiments.

The 42 and 43 Experiments.

AN EXPLICATION OF RAREFACTION.

An Explication of the Rota Aristotelica.

The Citations Englished.

A Summary of the Contents of the several Chapters.

PART I.

CHAP. I.

CHAP. II.

CHAP. III.

CHAP. IV.

CHAP. V.

CHAP. VI.

PART II.

CHAP. I.

CHAP. II.

CHAP. III.

CHAP. IV.

CHAP. V.

PART III.

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Title page

THE PREFACE.

AN EXAMEN Of the greatest Part of Mr. HOBBS's DIALOGUS PHYSICUS De Natura Aeris.

CHAP. I. The Occasion and Scope of the present Treatise.

CHAP. II. Of some mistakes of Mr. Hobbs touching matters of fact, and the Author's Doctrine.

CHAP. III. Wherein the Weight and Spring of the Air are asserted against Mr. Hobbs.

CHAP. IV. Wherein Mr. Hobbs's principal Explications of the Phaenomena of the Authors Engine are Examined.

CHAP. V. In which divers scattered Explications and other passages in Mr. Hobbs's Dialogue are examined.

CHAP. VI. Wherein other passages of Mr. Hobbs's Dialogue that concern the Author are examin'd

CHAP. VII. (Being an APPENDIX to the past Discourse) Wherein is examin'd what Mr. Hobbs teaches concerning Fluidity and Firmness.

The Citations English'd

A Summary of the Contents of the several Chapters.

CHAP. I.

CHAP. II.

CHAP. III.

CHAP. IV.

CHAP. V.

CHAP. VI.

CHAP. VII. (Being an Appendix to the past Discourse)

A CATALOGUE Of all the PHILOSOPHICAL WORKS Published by our AUTHOR.

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New Experiments PHYSICO-MECHANICAL, Touching the AIR

The Third Edition.

Whereunto is added A DEFENCE of the Author's EXPLICATION OF THE EXPERIMENTS, Against the OBJECTIONS OF FRANCISCUS LINUS And, THOMAS HOBBS.

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NEW EXPERIMENTS PHYSICO-MECHANICAL, Touching The SPRING of the AIR, and its EFFECTS, Made, for the most part, in a New Pnuematical Engine, Written by way of LETTER To the Right Honorable CHARLES Lord Vicount of DUNGARVAN, Eldest Son to the EARL of CORKE.

By the Honorable ROBERT BOYLE Esq

LONDON, Printed by Miles Flesher for Richard Davis, Bookseller in Oxford, MDCLXXXII.

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To the Reader.

ALthough the following Treatise being far more prolix than becomes a Letter, and than I at first intended it; I am very unwilling to encrease the already excessive bulk of the Book by a Preface, yet there are some Particulars that I think my self oblig'd to take notice of to the Reader, as things that will either concern him to know, or me to have known.

In the first place then: If it be demanded why I publish to the World a Letter, which by its Style and diverse Passages, appears to have been written as well For, as To a particular Person; I have chiefly these two things to answer: The one, That the Experiments therein related, having been many of them try'd in the presence of Ingenious Men; and by that means having made some noise among the Virtuosi (insomuch that some of them have been sent into Foreign Countries, where they have had the luck not to be despis'd) I could not, without quite tyring more than one Amanuensis, give out half as many Copies of them as were so earnestly desired, that I could not civilly refuse them. The other, That intelligent Persons in matters of this kind, perswade me, that the publication of what I had observ'd touching the nature of the Air, would not be useless to the World; and that in an Age so taken with Novelties as is ours, these new Experiments would be gratefull to the Lovers of free and real Learning: So that I might at once comply with my grand Design of promoting Experimental and Usefull Philosophy, and obtain the great satisfaction of giving some to ingenious Men; the hope of which, is, I confess, a temptation that I cannot easily resist.

Of my being somewhat prolix in many of my Experiments, I have these Reasons to render, That some of them being altogether new, seem'd to need the being circumstantially related, to keep the Reader from distrusting them: That divers Circumstances I did [Page] here and there set down for fear of forgetting them, when I may hereafter have occasion to make use of them in my other Writings: That in divers cases I thought it necessary to deliver things circumstantially, that the Person I addressed them to might, without mistake, and with as little trouble as is possible, be able to repeat such unusual Experiments: and that after I consented to let my Observations be made publick, the most ordinary reason of my prolixity was, That foreseeing that such a trouble as I met with in making those trials carefully, and the great expence of time that they necessarily require (not to mention the charges of making the Engine, and imploying a Man to manage it) will probably keep most Men from trying again these Experiments: I thought I might do the generality of my Readers no unacceptable piece of service, by so punctually relating what I carefully observ'd, that they may look upon these Narratives as standing Records in our new Pneumaticks, and need not reiterate themselves an Experiment to have as distinct an Idea of it, as may suffice them to ground their Reflexions and Speculations upon.

And because sometimes '-tis the Discourse made upon the Experiment that makes it appear prolix, I have commonly left a conspicuous interval betwixt such Discourses, and the Experiments whereunto they belong, or are annexed; that they who desire only the Historical part of the account we give of our Engine, may reade the Narratives, without being put to the trouble of reading the Reflexions too: which I here take notice of for the sake of those that are well vers'd in the New Philosophy, and in the Mathematicks; that such may skip what was design'd but for such Persons as may be less acquainted, even than I, with matters of this nature (scarce so much as mentioned by any Writer in our Language) and not for them from whom I shall be much more forward to learn, than to pretend to teach them. Of my being wont to speak rather doubtfully, or hesitantly, than resolvedly, concerning matters wherein I apprehend some difficulty, I have in another Treatise (which may, through God's assistance, come abroad ere long) given a particular, and, I have, a satisfactory account: wherefore I shall now defend my practice but by the Observation of [Page] Aristotle, who somewhere notes, That to seem to know all things certainly, and to speak positively of them, is a trick of bold and young Fellows: whereas those that are indeed intelligent and considerate, are wont to imploy more wary and diffident expressions, or (as he speaks) [...].

There are divers Reflexions, and other Passages in the following Epistle, and even some Experiments (occasionally mention'd) which may seem either impertinent or superfluous, but are not so: Being purposely written, either to evince some truth oppos'd, or disprove some erroneous conceit maintain'd by some eminent New Philosopher, or by some other Ingenious Men, who, I presum'd, would easily forgive me the having on such occasions purposely omitted their Names; though an inquisitive Person will probably discover divers of them, by the mention of the Opinions disprov'd in the Experiments I am excusing.

Ever since I discern'd the usefulness of speculative Geometry to Natural Philosophy, the unhappy Distempers of my Eyes, have so far kept me from being much conversant in it, that I fear I shall need the pardon of my Mathematical Readers, for some Passages, which, if I had been deeply skill'd in Geometry, I should have treated more accurately.

And indeed, having, for Reasons elsewhere deduc'd, purposely kept my self a stranger to most of the new Hypotheses in Philosophy, I am sensible enough that the Engine I treat of hath prevail'd with me to write of some subjects which are sufficiently remote from those I have been most conversant in. And having been reduc'd to write the greatest part of the ensuing Letter at a distance, not only from my Library, but from my own Manuscripts, I cannot but fear that my Discourses do not only want many choice things wherewith the Learned Writings of others might have enriched or imbelished them: But that partly for this reason, and partly for that touch'd upon a little before, It is possible I may have mention'd some Notions already publish'd by others, without taking notice of the Authors, not out of any design to defraud deserving Men, but for want of knowing such particulars to have been already publish'd by them: Especially the Experiments of our Engine being themselves sufficient to hint such Notions as we build upon them.

[Page]The order of the Experiments every Reader may alter, as suits best with his own design in perusing them: For not only all those betwixt whom there is an Affinity in Nature (by belonging to one subject) are not always plac'd one by another, but they are not still set down so much as in the order wherein they were made; but most commonly in that casual one wherein my occasions induc'd me to dispatch them to the Press. And, which is worse, I did usually send quite away the former Experiments, before the later were written, or perhaps so much as made: Whereby I lost the advantage of correcting and supplying the Imperfections of what I had formerly written, by the light of my subsequent Trials and Discoveries.

Besides all this, the distemper in my Eyes forbidding me not only to write my self so much as one Experiment, but even to reade over my self what I dictated to others: I cannot but fear, that besides the Author's mistakes, this Edition may be blemish'd by many, that may be properly imputed to a very unskilfull Writer (whom I was oftentimes by haste, reduc'd against my custome, to imploy) and may have escaped the Diligence of that Learned Friend, that doth me the favour to oversee the Press; especially, there being the distance of two days Journey betwixt it and me.

I need not, perhaps, represent to the equitable Reader, how much the strange Confusions of this unhappy Nation, in the midst of which I have made and written these Experiments, are apt to disturb that calmness of mind, and undistractedness of Thoughts, that are wont to be requisite to Happy Speculations. But I presume, that by all these things put together, he will readily perceive, That I have been so far from following the Poet's prudent Counsel touching the flow Publication of Books design'd to purchase credit by,

—Nonumque prematur in Annum

that I suffer this Treatise to come abroad into the World with a multitude of disadvantages.

But if it be demanded, why then I did not make it fitter for the Press before I sent it thither? my Answer must be, That not at first imagining that this sort of Experiments would prove any thing [Page] near so troublesome, either to make, or to record, as I afterwards found them, I did, to engage the Printer to dispatch, promise him to send him the whole Epistle in a very short time: So that although now and then the occasional vacations of the Press, by reason of Festivals, or the absence of the Corrector, gave me the leisure to exspatiate upon some subject; yet being oftentimes call'd upon to dispatch the Papers to the Press, my promise, and many unexpected Avocations, obliged me to a haste, which, though it hath detracted nothing from the Faithfulness of the Histerical part of our Book, hath (I fear) been disadvantageous enough to all the rest. And I made the less scruple to let the following Papers pass out of my hands, with all their Imperfections; because, as the Publick Affairs, and my own, were then circumstanc'd, I knew not when, (if at all) I should be again in a condition to prosecute Experiments of this kind; especially, since (to omit my being almost weary of being, as it were, confin'd to one sort of Experiments) I am pre-ingag'd (if it please God to vouchsafe me Life and Health) to imploy my first leisure in the publication of some other Physiological Papers, which I thought'twould make me much the fitter to take in hand, if I first dispatch'd all that I had at this time to write touching our Engine.

I have this farther to add, by way of Excuse, That as it hath been my design in publishing these Experiments to gratifie Ingenious Men; so, if I have not been much flattered, I may hope that the various hints to be met with in the following Letter, will (at least) somewhat awaken Mens thoughts, and excite them to new Speculations (such as perhaps even inquisitive Men would scarce else light upon) and I need not despair, that even the examination of such new Suspicions and Enquiries will hence also, at least occasionally, be facilitated: I said occasionally, because it being, as'tis proverbially said, Facile Inventis addere: It seems not irrational to expect, that our Engine it self, and divers of our Experiments, will be much promoted by the industry of Inventive and Mathematical Wits, whose Contrivances may easily either correct or supply, and consequently surpass many of those we have made use of. And, particularly, if Men by skill and patience can arrive both to evacuate such [Page] Receivers as ours, till there be no more Air left in them, than there seems to have remain'd in the Glasses made use of about the Magdeburgick Experiment (hereafter to be mentioned) and to keep out the Air for a competent while, the Usefulness and Discoveries of our Engine, will not be a little advanc'd. And perhaps that may belong to it, which I remember Seneca speaks of Nature: Initiatos (saith he) nos credimus, in Vestibulo ejus haeremus: For being now in a place where we are not quite destitute of moderately skilfull Artificers, we have since the Conclusion of the following Letter, made some Additions to our Engine, by whose help we find (upon some new trials) that we may be able, without much of new trouble, to keep the ambient Air out of the exhausted Receiver for a whole day; and perhaps we should be able to keep it out much longer, if before we shall have dispatch'd some urgent Affairs, and publish'd some Papers for which a kind of Promise is thought to make us Debtors to the Press, we could be at leisure to prosecute such Experiments, as may possibly afford a Supplement to the following Treatise, from which I shall now no longer detain the Reader.

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Friendly Reader,

I Know all Persons that have a publick Spirit for the Advancement of Learning, will think much that this piece came not out in a Language of more general Use, than this you see it now attir'd in; especially since the Excellent Noble Person, who is the Author, is known to be well able himself (being almost universally a Linguist) to have given it either the Old Latine, or the Newer French Dress.

But if it be an Honour to a Language to be preferr'd, and this Honour breeds sometimes an Emulation, as anciently it did between the Greeks and Romans, it cannot be thought unhandsome for an English Nobleman to have preferr'd his own: And it may be a sufficient Reason for the Gentry of Foreign Parts to learn our Speech, or keep Interpreters, that they are sure to have for their requital, from many of our English Writers (as here from this Piece) much curiously ingenious, and profitable Learning.

But as to this Particular (give me leave to use words from a Story) Since the Mountain cannot come to Mahomet, Mahomet will go to the Mountain: I mean thus; Because many witty Men, Persons of Honour and Estate especially, may be suppos'd to be able to make a better account, by employing their Studies and Time on Matter than Words, and so are justly impeded from learning Languages; And because (as I may judge) the Noble Author is willing to oblige all Men, He hath already provided, that this Piece [Page] shall shortly be done into Latine, that so it may come home to divers worthy Persons in its Stream, who cannot travel to find it out in its first Origine.

Having therefore leave so to do, I cannot forbear to give the World the Advertisement of this Latine Edition, lest some skilfull Artist should take needless pains about a work, which will ere long (by God's furtherance) be done to his Hands; For such unprofitable expences of Study have too frequently hapened, and too much to the disadvantage of Learning, for want of a sufficient Correspondence and intercourse between such as are exercised in the Mines of Wisedom.

This is all the trouble I shall at present give you: Nor shall I need mind you, if you have a true gust for the Book you reade, to have an honour and thankfull regard to the Person that hath favour'd us with the Communication of these his Trials, and is manifestly so great a Patron and Friend to Experimental Learning, and all true Wisedom; for should you fail in this, you might deservedly be depriv'd of some other Observations on the same subject, which the Author, I hear, hath made since the finishing of this Treatise.

I desire to be excused that I do not make Excuses for the slowness of the Publication, hoping that the long expectation you have had of it, will enhance, and not diminish your delight in the enjoyment of a piece like to be, amongst the Students in accurate Philosophy, of so general acceptance. Farewell.

R. Sh.

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A SUMMARY of the chief Matters treated of in this Epistolical Discourse.

THe Proaemium wherein is set down the occasion of this discourse. 1. The motives that induc'd the Author thereunto. 2. The hints he received 3. The things wherein this Engine excels any that have yet been made use of. 4. The description of the Engine and its parts, 5 &c. The way of preparing and using it, 8 &c. The division of the Experiments triable thereby into two sorts, and the difficulty of excluding the Air.

10, &c.

The first Experiment, touching the manner of pumping out the Air, and by what degrees the Receiver is emptied, 11, &c. A digression touching the Spring or Elastical power of the Air, with an attempt for a Mechanical Explication thereof, necessary to be premis'd for the explanation of the Phaenomena, exhibited in this and the subsequent Experiments.

12, &c.

The second Experiment, touching the pressure of the Air against the sides of the Bodies it invirons, 20, &c. with a digressive Explication of the pressure of the Air included within an ambient Body.

21 &c.

The third Experiment, touching the force requisite to draw down the Sucker, 23 &c. The Opinion of an eminent Modern Naturalist examin'd.

24 &c.

The fourth Experiment, touching the swelling of a Bladder; with the degrees by which it increaseth, 25 &c. Another Opinion of a Learned Author examin'd,

26 &c.

The fifth Experiment, touching the breaking of a Bladder in the Receiver. And of another by heat.

27, 28.

The sixth Experiment, of divers ways by which the elastical expansion of the Air was measur'd.

29, &c.

The seventh Experiment, touching what Figure doth best resist the pressure of the Air.

33

The eight Experiment, tending to a farther Demonstration of the former, from the breaking of a glass Helmet inward.

34

The ninth Experiment contains a farther confirmation from the breaking of a Glass outward, 35 &c. with an Experiment to prove, that these Phaenomena proceed not from an invincible Fuga vacui, 37. A description of other small Receivers, and their conveniencies, 38 &c. A Receipt for the making of a Composition to cement crack'd Glasses.

39

The tenth Experiment, touching the flaming of Candles inclosed in the Receiver.

39 &c.

The eleventh Experiment, touching the burning of Coals: and the lasting of the excandescence of an included piece of Iron.

42

The twelfth Experiment, concerning the burning of Match.

44

The thirteenth Experiment, concerning the farther prosecution of the preceding, tending to prove the extinction of the Fire in the former Experiments, not to have proceeded from the pressure of the Fire by the Fumes. Some remarkable Circumstances of it. The Experiment of Match try'd in a Small Receiver.

45 &c.

The fourteenth Experiment, touching the striking Fire, and klindling of Powder [Page] with the Lock of a Pistol in the evacuated Receiver.

47 &c.

The fifteenth Experiment, touching the unsuccessfulness of kindling included Bodies with a Burning-glass, and the Author's intention to prosecute it farther.

49

The sixteenth Experiment, concerning the operation of the Loadstone.

52

The seventeenth Experiment, touching the gradual descent of the Quick-silver in the Torricellian Experiment, 51 &c. Some observable Circumstances concerning it, 54 &c. The same Experiment try'd in one of the small Receivers, 55. How this Experiment may be made use of to know the strength of the pressure of the Air for every degree of Rarefaction, 56 &c. The trial of the same Experiment in a Tube not two foot long, 57. The raising of the Mercurial Cylinder, by the forcing of more Air into the Receiver, ib. Some Allegation for and against a Vacuum considered, 59 &c. Some Advertisements concerning the inconveniencies that may arise from the diversity of measures made use of for the defining the altitude of the Mercurial Cylinder; and from the neglect of little parcels of Air apt to remain between the Mercury and the concave surface of the Tube, 60 &c. Some Expedients for the more exact filling the Tube, 61. The height the Author once found of the Mercurial Cylinder, according to English measure.

63

The eighteenth Experiment, containing a new Observation touching the variation of the height of the Mercurial Cylinder in the same Tube, with an offer at the Reason thereof.

63 &c.

The nineteenth Experiment, touching the subsiding of a Cylinder of Water, 69. The same try'd in a small Receiver.

70

The twentieth Experiment, touching the Elater of Water, with a digressive Experiment to the same purpose.

71 &c.

The 21 Experiment, being a prosecution of the former Enquiry, by experimenting the Generation of Bubbles under Water, a recital of some not able Circumstances, with some observable Corollaries deduc'd therefrom.

73 &c.

The 22 Experiment, tending to a determination of the Enquiry propos'd in the former Experiment, by proving the matter of these Bubbles from their permanency to be Air: The Experiments try'd in the great and small Receivers, evincing the same thing, 77 &c. An Experiment wherein there appear'd Bubbles in Quick-silver, 79. The Author's Inference, 80. A digressive Enquiry, whether or no Air may be generated anew; with several Histories and Experiments, tending to the resolving and clearing thereof, ibid. &c. The Author's excuse for so long a digression.

90

The 23 Experiment, containing a farther enquiry touching Bubbles made with common and distill'd Water.

91

The 24 Experiment, wherein the enquiry is prosccuted with other Liquors, as with Sallet Oyl, Oyl of Turpentine, a Solution of Tartar, Spirit of Vinegar, Red-Wine, Milk, Hens Eggs, Spirit of Urine, Spirit of Wine and Water, Spirit of Wine. 94 &c. The wonderfull expansion of the Spirit of Wine.

97

The 25 Experiment, touching the expansion and gravity of the Air under Water.

98 &c.

The 26 Experiment, touching the Vibrations of a Pendulum.

102 &c.

The 27 Experiment, touching the propagation [Page] of sound: and the Author's intention of trying some other Experiments, for the further elucidation thereof.

103

The 28 Experiment, touching the sudden eruption of Bubbles from the Water, when the Air's pressure was speedily remov'd.

108

The 29 Experiment, touching the cause of the ascent of Fumes and Vapors, wherein't is prov'd (from the several motions, (which the Fumes of a strange smoking Liquor, of the Author's, were observ'd to have in the Receiver, upon the exsuction of the Air) that the reason of their ascent proceeds from the gravity of the ambient Air, and not from any positive levity of their own.

110 &c.

The 30 Experiment, concerning the nature of a fluid Body, illustrated by the example of smoke, which in several circumstances seems very much to resemble the property of a fluid Body, 113. A conjecture of the cause of the Sun's undulation.

115

The 31 Experiment, concerning the Phaenomena of two flat Marbles exactly plain'd and wrought together, and the true reason thereof. The Author's intention for the further prosecution thereof, and what hindred him; the reason why the under Marble did not fall from the upper (being only conjoyn'd with Spirit of Wine) when the Receiver was evacuated. And a notable relation concerning the cohesion of flat Bodies.

116 &c.

The 32 Experiment, touching the forcible pressure of the Air against the outward Superficies of a Valve, fasten'd upon the Stop-cock of the Receiver. The Diameter of it, and the weight it sustain'd.

118 &c.

The 33 Experiment, touching the great pressure of the Air against the under Superficies of the Sucker, 120 &c. what weight was requisite to depress it, and what weight it would lift and carry up with it, 121 &c. What improvement and use there may be made of this Experiment, ib. A Discourse touching the nature of Suction, proving that Suga vacui is not the adequate cause thereof.

123 &c.

The 34 Experiment, containing several attempts for the weighing of light Bodies in the exhausted Receiver.

131 &c.

The 35 Experiment, touching the cause of a Filtration, and the rising of mater in Siphons, 133 &c. A relation of a new kind of Siphon, of the Author's, upon the occasion of trying the Experiment lately observ'd by some French-men, and further improv'd by himself; and some conjectures touching the cause of the exhibited Phaenomena.

136 &c.

The 36 Experiment, touching the weighing of a parcel of Air in the exhausted Vessel; and some other Observations for the explication thereof, 138 &c. An accidental Experiment, tending to the further confirmation of the Author's Reflexions upon the first Experiment; with a digressive observation, noting the subtile penetrancy of some Spirits, to exceed by far that of the Air, 140 &c. and some other Experiments to shew the difficulty of the ingress of the Air into the pores or holes of some Bodies into which water will readily insinuate it self, with a conjecture at the cause thereof, 142. The Author returns to the prosecution of the inquiry after the gravity of the Air: But first, (upon the occasion of the tenacity of a thin Bubble of Glass) sets down his thoughts concerning the strange exuperancy of strength in Air, agitated by heat, above [Page] what the same hath unagitated: and then proceeds to the examination of the weight of the Air by an AEolipile, and compares the result thereof, with that of Mersennus, 143, 144 &c. The Opinions and Experiments of divers Authors, and some of his own, touching the proportion of weight betwixt Water and Air, are compar'd and examin'd by the Author, 145. The result thereof, ibid. Mersennus his Observation reconciled, with that of the Author; and the proportion between the gravity of Water and Air about London, 146 &c. After the recital of the Opinions of several Writers, touching the proportion of gravity between Water and Quick-silver, the Author sets down his own trials, made several ways, together with his conclusion therefrom, 147 &c. The use he makes of this inquiry for the ghessing at the height of the Atmosphere, 148. what other Experiments are requisite to the determination thereof.

149

The 37 Experiment, touching the strange and odd Phaenomenon, of the sudden flashes of light in the cavity of the Receiver; the several circumstances and difficulties of it, with some attempts towards the rendring a reason thereof, 153 &c. The difficulty of so doing farther shown from the consideration of the various changes of Air which do not immediately fall under our senses: This last proposition prov'd by several Observations.

156, 157

The 38 Experiment, touching the freezing of Water. A problem (concerning the great force wherewith a freezing Liquor extends it self) proposed upon the consideration of divers admirable effects wrought thereby.

162

The 39 Experiment, containing an inquisition after the temperature of the substance that remained in the cavity of the Receiver, after the Air was well exhausted. The relation of a Phaenomenon, seeming to proceed from the swelling of the Glass: with an advertisement concerning the pliableness of Glass in small pieces.

164

The 40 Experiment, touching the difficulty that occurred in making trial whether rarefied Air were able to sustain flying Insects.

166

The 41 Experiment, exhibiting several trials touching the respiration of divers sorts of Animals included in the Receiver, 167 &c. with a digression containing some doubts touching Respiration, wherein are delivered several Experiments relating thereunto.

171

The 42 Experiment, touching the differing operation of corrosive Liquors in the emptied Receiver and in the open Air.

196

The 43 Experiment, touching the spontaneous Ebullition of warm Liquors in the exhausted Receiver.

198

The Conclusion.

201

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TO THE LORD of DUNGARVAN, My Honored and Dear NEPHEW.

My Dear Lord,

REceiving in your last from Paris, a desire that I would adde some more Experiments to those I formerly sent You over: I could not be so much your Servant as I am, without looking upon that Desire as a Command; and consequently, without thinking my self obliged to consider by what sort of Experiments it might the most acceptably be obey'd. And at the same time, perceiving by Letters from some other Ingenious Persons at Paris, that several of the Virtuosi there, were very intent upon the examination of the Interest of the Air, in hindring the descent of the Quick-silver, in the famous Experiment touching a Vacuum: I thought I could not comply with your Desires in a more fit and seasonable manner, than by prosecuting and endeavouring to promote that noble Experiment of Torricellius: and by presenting Your Lordship an account of my attempts to illustrate a Subject, about which (its being so much discours'd of where you are, together with your inbred Curiosity, and love of Experimental Learning) made me suppose you sufficiently inquisitive.

And though I pretend not to acquaint you, on this occasion, with any store of new Discoveries, yet possibly I shall be so happy, as to assist you to know some things which you did formerly but suppose; and shall present you, if not with new Theories, at least with new Proofs of such as are not yet become unquestionable. And if what I shall deliver, hath the good fortune to encourage and assist you to prosecute the Hints it will afford, I shall account my self, in paying of a duty to you, to have done a piece of Service to the Commonwealth [Page] of Learning. Since it may highly conduce to the advancement of that Experimental Philosophy, the effectual pursuit of which, requires as well a Purse as a Brain, to endear it to hopefull Persons of your Quality: who may accomplish many things, which others can but wish, or at most, but design, by being able to imploy the Presents of Fortune in the search of the Mysteries of Nature.

And I am not faintly induc'd to make choice of this Subject, rather than any of the expected Chymical ones, to entertain Your Lordship upon, by these two Considerations: The one, That the Air being so necessary to humane Life, that not only the generality of Men, but most other Creatures that breathe, cannot live many minutes without it; any considerable discovery of its Nature, seems likely to prove of moment to Mankind. And the other is, That the ambient Air, being that whereto both our own Bodies, and most of the others we deal with here below, are almost perpetually contiguous; not only its alterations have a notable and manifest share in those obvious Effects, that Men have already been invited to ascribe thereunto (such as are the various Distempers incident to humane Bodies especially if crazy in the Spring, the Autumn, and also on most of the great and sudden changes of Weather) but likewise, the further discovery of the Nature of the Air, will probably discover to us, that it concurs more or less to the exhibiting of many Phaenomena, in which it hath hitherto scarce been suspected to have any Interest. So that a true account of any Experiment that is New concerning a thing, wherewith we have such constant and necessary intercourse, may not only prove of some advantage to humane Life, but gratifie Philosophers, by promoting their Speculations on a Subject which hath so much opportunity to solicite their Curiosity.

And I should immediately proceed to the mention of my Experiments, but that I like too well that worthy saying of In Praefat. lib. 1. the Naturalist Pliny, Benignum est & plenum ingenui[Page]pudoris, fateri per quos profeceris, not to conform to it, by acquainting your Lordship, in the first place, with the Hint I had of the Engine I am to entertain you with. You may be pleas'd to remember, that a while before our separation in England, I told you of a Book that I had heard of, but not perus'd, publish'd by the industrious Jesuit Schottus, wherein 'twas said, He related how that ingenious Gentleman, Otto Gericke, Consul of Magdeburg, had lately practis'd in Germany a way of emptying Glass Vessels, by sucking out the Air at the mouth of the Vessel, plung'd under Water: And you may also perhaps remember, that I express'd my self much delighted with this Experiment, since thereby the great force of the external Air (either rushing in at the open'd Orifice of the empty'd Vessel, or violently forcing up the Water into it) was rendred more obvious and conspicuous than in any Experiment that I had formerly seen. And though it may appear by some of those Writings I sometimes shew'd your Lordship, that I had been solicitous to try things upon the same ground; yet in regard this Gentleman was before-hand with me in producing such considerable Effects, by means of the exsuction of Air, I think myself oblig'd to acknowledge the assistance and encouragement, the Report of his Performances hath afforded me.

But, as few inventions happen to be at first so compleat, as not to be either blemished with some deficiencies needful to be remedi'd, or otherwise capable of improvement: so when the Engine we have been speaking of, comes to be more attentively consider'd, there will appear two very considerable things to be desir'd in it. For first, the Wind Pump (as some body not improperly calls it) is so contriv'd, that to evacuate the Vessel, there is requir'd the continual labour of two strong Men for divers hours. And next (which is an imperfection of much greater moment) the Receiver, or Glass to be empty'd, consisting of one entire and uninterrupted Globe and Neck of Glass; the whole Engine is so made, that things cannot be convey'd into it, [Page] whereon to try Experiments: So that there seems but little (if any thing) more to be expected from it, than those very few Phaenomena that have been already observ'd by the Author, and recorded by Schottus. Wherefore to remedy these Inconveniences, I put both Mr.G. and R. Hook (who hath also the Honour to be known to your Lordship, and was with me when I had these things under consideration) to contrive some Air Pump, that might not, like the other, need to be kept under Water (which on divers occasions is convenient) and might be more easily manag'd: And after an unsuccessful tryal or two of ways propos'd by others, the last nam'd Person fitted me with a Pump, anon to be describ'd. And thus the first Imperfection of the German Engine, was in good measure, though not perfectly remedy'd: And to supply the second defect, it was considered that it would not perhaps prove impossible to leave in the Glass to be empty'd, a hole large enough to put in a Man's Arm cloath'd; and consequently other Bodies, not bigger than it, or longer than the inside of the Vessel. And this Design seem'd the more hopeful, because I remembred, that having several years before often made the Experiment De Vacuo with my own hands; I had, to examine some Conjectures that occurr'd to me about it, caused Glasses to be made with a hole at that end, which uses to be seal'd up, and had nevertheless been able, as occasion requir'd, to make use of such Tubes, as if no such holes had been left in them, by devising stopples for them, made of the common Plaister call'd Diachylon: which I rightly enough guess'd, would, by reason of the exquisite commixtion of its small parts, and closeness of it's texture, deny all access to the external Air. Wherefore, supposing that by the help of such Plaisters carefully laid upon the commissures of the stopple and hole to be made in the Receiver, the external Air might be hindred from insinuating it self between them, into the Vessel, we caus'd several such Glasses, as you will find describ'd a little lower, to be blown at the Glass-house; and though we could [Page] [Page]

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[Page] not get the Work-men to blow any of them so large, or of so convenient a shape as we would fain have had; yet finding one to be tolerably fit, and less unfit than any of the rest, we were content to make use of it in that Engine: Of which, I suppose, you by this time expect the Description, in order to the recital of the Phaenomena exhibited by it.

To give your Lordship then, in the first place, some account of the Engine it self: It consists of two principal parts; a glass Vessel, and a Pump to draw the Air out of it.

The former of these (which we, with the Glass-men, shall often call a Receiver, for its affinity to the large Vessels of that name, used by Chymists) consists of a Glass with a wide hole at the top, of a cover to that hole, and of a Stop-cock fastned to the end of the Neck, at the bottom.

The shape of the Glass, you will find express'd in the first Figure of the annexed Scheme. And for the size of it, it contain'd about 30 Wine Quarts, each of them containing near two Pound (of 16 Ounces to the Pound) of Water: We should have been better pleas'd with a more capacious Vessel, but the Glass-men professed themselves unable to blow a larger, of such a thickness and shape as was requisite to our purpose.

At the very top of the Vessel, (A) you may observe a round hole, whose Diametre (BC) is of about four Inches; and whereof, the Orifice is incircled with a lip of Glass, almost an Inch high: For the making of which lip, it was requisite (to mention that upon the by, in case your Lordship should have such another Engine made for you) to have a hollow and tapering Pipe of Glass drawn out, whereof the Orifice above mentioned was the Basis, and then to have the Cone cut off with an hot Iron, within about an Inch of the Points (BC.)

The use of the lip, is to sustain the cover delineated in the second Figure; where (DE) points out a brass Ring, so cast, as that it doth cover the lip (BC) of the first Figure, and is cemented on, upon it, with a strong and close Cement. To the inward tapering Orifice of this Ring (which is about three [Page] Inches over) are exquisitely ground the sides of the Brass stopple (FG;) so that the concave superficies of the one, and the convex of the other, may touch one another in so many places, as may leave as little access, as possible, to the external Air: And in the midst of this cover is left a hole (HI) of about half an Inch over, invironed also with a Ring or Socket of the same Metal, and fitted likewise with a Brass stopple (K) made in the form of the Key of a Stop-cock, and exactly ground into the hole (HI) it is to fill; so as that, though it be turn'd round in the cavity it possesses, it will not let in the air, and yet may be put in or taken out at pleasure, for uses to be hereafter mentioned. In order to some of which, it is perforated with a little hole, (8) traversing the whole thickness of it at the lower end; through which, and a little Brass Ring (L) fastned to one side (no matter which) of the bottom of the stopple (FG) a string (8, 9, 10.) might pass, to be imploy'd to move some things in the capacity of the empty'd Vessel, without any where unstopping it.

The last thing belonging to our Receiver, is the Stop-cock, designed in the first Figure by (N,) for the better fastening of which to the neck, and exacter exclusion of the Air, there was soder'd on to the shank of the Cock (X) a Plate of Tin, (MTUW) long enough to cover the neck of the Receiver. But because the cementing of this was a matter of some difficulty, it will not be amiss to mention here the manner of it; which was, That the cavity of the Tin Plate was fill'd with a melted Cement, made of Pitch, Rosin, and Wood ashes, well incorporated; and to hinder this liquid Mixture from getting into the Orifice (Z) of the shank (X,) that hole was stop'd with a Cock, to which was fastned a string, whereby it might be pull'd out at the upper Orifice of the Receiver; and then, the Glass neck of the Receiver being well warm'd, was thrust into this Cement, and over the shank, whereby it was effected, that all the space betwixt the Tin Plate and the Receiver, and betwixt the internal superficies of the Receiver, and the shank of the Cock, was fill'd with the Cement; and so we have dispatch'd the first upper part of the Engine.

[Page] The undermost remaining part consists of a Frame, and of a sucking Pump, or as we formerly call'd it, an Air Pump, supported by it: The Frame is of Wood, small, but very strong, consisting of three legs, (111) so plac'd, that one side of it may stand perpendicular, that the free motion of the hand may not be hindered. In the midst of which frame, is transversly nail'd a board, (222) which may not improperly be call'd a Midriff, upon which rests, and to which is strongly fastned, the main part of the Pump it self, which is the only thing remaining to be described.

The Pump consists of four parts, a hollow Cylinder, a Sucker, a handle to move that Sucker, and a Valve.

The Cylinder was (by a pattern) cast of Brass; it is in length about 14 Inches, thick enough to be very strong, notwithstanding the Cylindrical cavity left within it; this cavity is about three Inches Diametre, and makes as exact a Cylinder as the Artificer was able to bore. This hollow Cylinder is fitted with a Sucker, (4455) consisting of two parts; the one (44) somewhat less in Diametre than the Cavity of the Cylinder; upon which is nail'd a good thick piece of tann'd Shoe-leather, which will go so close to the Cylinder, that it will need to be very forcibly knock'd and ram'd in, if at any time it be taken out; which is therefore done, that it may the more exactly hinder the Air from insinuating it self betwixt it and the sides of the Cylinder whereon it is to move.

To the midst of this former part of the Sucker is strongly fastned the other; namely, a thick and narrow plate of Iron (55) somewhat longer than the Cylinder, one of whose edges is smooth, but at the other edge it is indented (as I may so speak) with a row of Teeth, delineated in the Scheme, into whose intervals are to be fitted, the Teeth of a small Iron Nut, (αβ) (as Tradesmen call it) which is fastned by two staples (22) to the underside of the formerly mention'd transverse board (222) on which the Cylinder rests, and is turn'd to and fro by the third piece of this Pump, namely, the handle or Manubrium, [Page] (7) of which the Figure gives a sufficient description.

The fourth and last part of this Cylinder, is the Valve, (R) consisting of a hole bored through at the top of the Cylinder, a little tapering towards the cavity; into which hole is ground a tapering Peg of Brass, to be thrust in, and taken out at pleasure.

The Engine being thus describ'd, it will be requisite to add, that something is wont to be done before it be set on work, for the more easie moving of the Sucker, and for the better exclusion of the outward Air: which, when the Vessel begins to be exhausted, is much more difficult to be kept out, than one would easily imagine.

There must then be first pour'd in at the top of the Receiver, a little sallad Oyl, partly to fill up any small intervals that may happen to be betwixt the contiguous surfaces of the internal parts of the Stop-cock: And partly, that it may be the more easie to turn the Key (S) backwards and forwards. Pretty store of Oyl must also be pour'd into the Cylinder, both that the Sucker may slip up and down in it the more smoothly and freely, and that the Air might be the better hindred from getting in between them: And for the like reasons, a little Oyl is to be used also about the Valve. Upon which occasion, it would not be omitted (for it is strange) that oftentimes, when neither the pouring in of Water, nor even of Oyl it alone, prov'd capable to make the Sucker move easily enough in the Cylinder; a mixture of both those Liquors would readily (sometimes even to admiration) perform the desired effect. And lastly, the Brass cover of the Receiver, being put into the Brass ring formerly describ'd, that no Air may get between them, it will be very requisite to plaister over very carefully the upper edges of both, with the Plaister formerly mentioned, or some other as close, which is to be spread upon the edges with an hot Iron; that, being melted, it may run into and fill up all the cranies, or other little cavities, at which the Air might otherwise get entrance.

All things being thus fitted, and the lower shank (O) of the [Page] Stop-cock being put into the upper Orifice of the Cylinder (and) into which it was exactly ground; the Experimenter is first, by turning the handle, to force the Sucker to the top of the Cylinder, that there may be no Air left in the upper part of it: Then shutting the Valve with the Plug, and turning the other way, he is to draw down the Sucker to the bottom of the Cylinder; by which motion of the Sucker, the Air that was formerly in the Cylinder being thrust out, and none being permitted to succeed in its room, 'tis manifest that the cavity of the Cylinder must be empty in reference to the Air. So that if thereupon the Key of the Stop-cock be so turn'd, as that through the perforation of it, a free passage be opened betwixt the Cylinder and the Receiver, part of the Air formerly contain'd in the Receiver, will nimbly descend into the Cylinder. And this Air being, by the turning back of the Key, hinder'd from the returning into the Receiver, may, by the opening of the Valve, and forcing up of the Sucker to the top of the Cylinder again, be driven out into the open Air. And thus by the repetition of the motion of the Sucker upward and downward, and by opportunely turning the Key, and stopping the Valve, as occasion requires, more or less Air may be suck'd out of the Receiver, according to the exigency of the Experiment, and the intention of him that makes it.

Your Lordship will, perhaps, think that I have been unnecessarily prolix in this first part of my Discourse: But if you had seen how many unexpected difficulties we found to keep out the external Air, even for a little while, when some considerable part of the internal had been suck'd out; You would peradventure allow, that I might have set down more circumstances than I have, without setting down any, whose knowledge, he that shall try the Experiment, may not have need of. Which is so true, that, before we proceed any further, I cannot think it unseasonable to advertise Your Lordship, that there are two chief sorts of Experiments, which we design'd in our Engine to make tryal of: The one, such as may be quickly dispatch'd, [Page] and therefore may be try'd in our Engine, though it leak a little, because the Air may be faster drawn out, by nimbly plying the Pump, than it can get in at undiscern'd leaks; I say at undiscern'd leaks, because such as are big enough to be discover'd, can scarce be uneasie to be stopt. The other sort of Experiments consist of those that require, not only that the internal Air be drawn out of the Receiver, but that it be likewise for a long time kept out of it. Such are the preservation of Animal and other Bodies therein, the germination and growth of Vegetables, and other trials of several sorts, which it is apparent cannot be well made, unless the external Air can, for a competent while, be excluded: Since, even at a very small leak, there may enough get in, to make the Vacuum soon lose that name; by which I here declare once for all, that I understand not a space wherein there is no Body at all, but such as is either altogether, or almost totally devoid of Air.

Now this distinction of Experiments I thought fit to premise to the ensuing Narratives, because, upon trial, we found it so exceeding (and scarce imaginably) difficult a matter, to keep out the Air from getting at all in at any imperceptible hole or flaw whatsoever, (in a Vessel immediately surrounded with the compressed Atmosphere,) that in spight of all our care and diligence, we never were able totally to exhaust the Receiver, or keep it when it was almost empty, any considerable time, from leaking more or less: although (as we have lately intimated) by unwearied quickness in plying the Pump, the internal Air can be much faster drawn out than the external can get in, till the Receiver come to be almost quite empty. And that's enough to enable Men to discover hitherto unobserved Phaenomena of Nature.

The Experiments therefore of the first sort, will, I fear, prove the only ones wherewith my Avocations will allow me to entertain Your Lordship in this Letter. For till your further Commands shall engage me to undertake, by God's permission, such an Employment, and more leasure shall better fit [Page] me for it, I know not whether I shall be in a condition to try what may be done, to enable me to give you some account of the other sort of Experiments also.

EXPERIMENT I.

TO proceed now to the Phaenomena, exhibited to us by the Engine above described; I hold it not unfit to begin with what doth constantly and regularly offer it self to our observation, as depending upon the Fabrick of the Engine it self, and not upon the nature of this or that particular Experiment which 'tis employed to try.

First, then, upon the drawing down of the Sucker (the Valve being shut) the Cylindrical space, deserted by the Sucker, is left devoid of Air; and therefore, upon the turning of the Key, the Air contained in the Receiver rusheth into the emptied Cylinder, till the Air in both those Vessels be brought to about an equal measure of dilatation. And therefore, upon shutting the Receiver by re-turning the Key, if you open the Valve, and force up the Sucker again, you will find, that after this first exsuction you will drive out almost a whole Cylinder full of Air: But at the following exsuctions, you will draw less and less of Air out of the Receiver into the Cylinder, because there will still remain less and less Air in the Receiver it self; and consequently, the Particles of the remaining Air, having more room to extend themselves in, will less press out one another. This you will easily perceive, by finding, that you still force less and less Air out of the Cylinder; so that when the Receiver is almost exhausted, you may force up the Sucker almost to the top of the Cylinder, before you will need to unstop the Valve to let out any Air: And if at such time, the Valve being shut, you let go the handle of the Pump, you will find the Sucker forcibly carried up to the top of the Cylinder, by the protrusion of the external Air; which, being much less rarified than that within the Cylinder; must have a more forcible pressure upon the Sucker, than the internal is able to resist: [Page] And by this means you may know how far you have emptied the Receiver. And to this we may add, on this occasion, that constantly upon the turning of the Key to let out the Air from the Receiver, into the emptied Cylinder, there is immediately produced a considerably brisk noise, especially whilst there is any plenty of Air in the Receiver.

For the more easie understanding of the Experiments triable by our Engine; I thought it not superfluous, nor unseasonable in the recital of this first of them, to insinuate that notion by which it seems likely that most, if not all of them, will prove explicable. Your Lordship will easily suppose, that the Notion I speak of is, That there is a Spring, or Elastical power in the Air we live in. By which [...] or spring of the Air, that which I mean is this: That our Air either consists of, or at least abounds with, parts of such a nature; that in case they be bent or compress'd by the weight of the incumbent part of the Atmosphere, or by any other Body, they do endeavour, as much as in them lieth, to free themselves from that pressure, by bearing against the contiguous Bodies that keep them bent; and, as soon as those Bodies are remov'd or reduced to give them way, by presently unbending and stretching out themselves, either quite, or so far forth as the contiguous Bodies that resist them will permit, and thereby expanding the whole parcel of Air, these elastical Bodies compose.

This Notion may perhaps be somewhat further explain'd, by conceiving the Air near the Earth to be such a heap of little Bodies, lying one upon another, as may be resembled to a Fleece of Wooll. For this (to omit other likenesses betwixt them) consists of many slender and flexible Hairs; each of which may indeed, like a little Spring, be easily bent or rouled up; but will also, like a Spring, be still endeavouring to stretch it self out again. For though both these Hairs, and the Aereal Corpuscles to which we liken them, do easily yield to external pressures; yet each of them (by virtue of its structure) is endow'd with a Power or Principle of self-Dilatation; by virtue where [Page] of, though the hairs may by a Man's hand be bent and crouded closer together, and into a narrower room than suits best with the nature of the Body, yet, whilst the compression lasts, there is in the fleece they compose an endeavour outwards, where by it continually thrusts against the hand that opposes its Expansion. And upon the removal of the external pressure, by opening the hand more or less, the compressed Wool doth, as it were, spontaneously expand or display itself towards the recovery of its former more loose and free condition, till the Fleece hath either regain'd its former Dimensions, or at least, approach'd them as near as the compressing hand (perchance not quite open'd) will permit. This Power of self-Dilatation, is somewhat more conspicuous in a dry Spunge compress'd, than in a fleece of Wool. But yet we rather chose to employ the latter, on this occasion, because it is not like a Spunge, an intire Body, but a number of slender and flexible Bodies, loosely complicated, as the Air it self seems to be.

There is yet another way to explicate the Spring of the Air, namely, by supposing with that most ingenious Gentleman, Monsieur Des Cartes, That the Air is nothing but a Congeries or heap of small and (for the most part) of flexible Particles; of several sizes, and of all kind of Figures which are rais'd by heat (especially that of the Sun) into that fluid and subtle Ethereal Body that surrounds the Earth; and by the restless agitation of that Celestial matter wherein those particles swim, are so whirld round, that each Corpuscle endeavours to beat off all others from coming within the little Sphere requisite to its motion about its own Centre; and (in case any, by intruding into that Sphere, shall oppose its free Rotation) to expel or drive it away: So that according to this doctrine, it imports very little, whether the particles of the Air have the structure requisite to Springs, or be of any other form (how irregular soever) since their Elastical power is not made to depend upon their shape or structure, but upon the vehement agitation, and (as it were) brandishing motion, which they receive from the fluid Ether that swiftly flows [Page] between them, and whirling about each of them (independently from the rest) not only keeps those slender Aëreal Bodies seperated and stretcht out (at least, as far as the Neighbouring ones will permit) which otherwise, by reason of their flexibleness and weight, would flag or curl; but also makes them hit against, and knock away each other, and consequently require more room, than that, which, if they were compress'd, they would take up.

By these two differing ways, my Lord, may the Springs of the Air be explicated. But though the former of them be that, which by reason of its seeming somewhat more easie, I shall for the most part make use of in the following Discourse: yet am I not willing to declare peremptorily for either of them, against the other. And indeed, though I have in another Treatise endeavoured to make it probable, that the returning of Elastical Bodies (if I may so call them) forcibly bent, to their former position, may be Mechanically explicated: Yet I must confess, that to determine whether the motion of Restitution in Bodies, proceed from this, That the parts of a Body of a peculiar Structure are put into motion by the bending of the Spring, or from the endeavor of some subtle ambient Body, whose passage may be oppos'd or obstructed, or else it's pressure unequally resisted by reason of the new shape or magnitude, which the bending of a Spring may give the Pores of it: To determine this, I say, seems to me a matter of more difficulty, than at first sight one would easily imagine it. Wherefore I shall decline medling with a Subject, which is much more hard to be explicated, than necessary to be so, by him, whose business it is not, in this Letter, to assign the adequate cause of the Spring of the Air, but only to manifest, That the Air hath a Spring, and to relate some of its effects.

I know not whether I need annex that, though either of the above-mention'd Hypotheses, and perhaps some others, may afford us an account plausible enough of the Air's Spring; yet I doubt, whether any of them gives us a sufficient account of its [Page] Nature. And of this doubt, I might here mention some Reasons, but that, peradventure, I may (God permitting) have a fitter occasion to say something of it elsew here. And therefore I shuold now proceed to the next Experiment, but that I think it requisite, first, to suggest to your Lordship what comes into my thoughts, by way of Answer to a plausible Objection, which I foresee you may make against our propos'd Doctrine, touching the Spring of the Air. For it may be alledged, that though the Air were granted to consist of springy Particles (if I may so speak) yet thereby we could only give an account of the Dilatation of the Air in Wind Guns, and other pneumatical Engines wherein the Air hath been compress'd, and its springs violently bent by an apparent external force; upon the removal of which, 'tis no wonder that the Air should, by the motion of restitution expand it self till it hath recovered its more natural dimensions: whereas in our above-mentioned first Experiment, and in almost all others triable in our Engine, it appears not, that any compression of the Air preceded its spontaneous Dilatation or Expansion of it self. To remove this difficulty, I must desire Your Lordship to take notice, that of whatever nature the Air, very remote from the Earth, may be, and whatever the Schools may confidently teach to the contrary, yet we have divers Experiments to evince, that the Atmosphere we live in, is not (otherwise than comparatively to more ponderous Bodies) light, but heavy: And did not their gravity hinder them, it appears not why the streams of the Terraqueous Globe, of which our Air in great part consists, should not rise much higher, than the Refractions of the Sun, and other Stars give men ground to think, that the Atmosphere, (even in the judgment of those Rescent Astronomers, who seem willing to enlarge its bounds as much as they dare,) doth reach.

But lest you should expect my seconding this Reason by Experience; and lest you should object, That most of the Experiments that have been propos'd to prove the gravity of the Air, have been either barely propos'd, or perhaps not accurately tri'd; [Page] I am content, before I pass further, to mention here. That I found a dry lambs-bladder containing near about two thirds of a pint, and compress'd by a packthred tied about it, to lose a grain and the eighth part of a grain of its former weight, by the recess of the Air upon my having prickt it: And this with a pair of Scales, which, when the full bladder and the correspondent weight were in it, would manifestly turn either way with the 32 part of a grain. And if it be further objected, That the Air in the Bladder was violently compress'd by the packthred and the sides of the Bladder, we might probably (to wave prolix answers) be furnish'd with a Reply, by setting down the differing weight of our Receiver, when empti'd and when full of uncompress'd Air, if we could here procure Scales fit for so nice an Experiment; since we are informed, that in the German Experiment, commended at the beginning of this Letter, the ingenious Triers of it found, That their Glass Vessel, of the capacity of 32 measures, was lighter when the Air had been drawn out of it, than before, by no less than one ounce and 3/10 that is, an ounce and very near a third: But of the gravity of the Air, we may elsewhere have occasion to make further mention.

Taking it then for granted that the Air is not devoid of weight, it will not be uneasie to conceive, That that part of the Atmosphere wherein we live, being the lower part of it, the Corpuscles that compose it, are very much compress'd by the weight of all those of the like nature that are directly over them; that is, of all the Particles of Air, that being pil'd up upon them, reach to the top of the Atmosphere. And though the height of this Atmosphere, according to the famous Kepler, and some others, scarce exceeds eight common miles; yet other eminent and later Astronomers, would promote the confines of the Atmosphere to exceed six or seven times that number of miles. And the diligent and learned Ricciolo makes it probable, that the Atmosphere may, at least in divers places, be at least fifty miles high. So that according to a moderate estimate of the thickness of the Atmosphere, we may well suppose, that a Column of Air, of [Page] many miles in height, leaning upon some springy Corpuscles of Air here below, may have weight enough to bend their little springs, and keep them bent: As, (to resume our former comparison,) if there were fleeces of Wooll pil'd up to a mountainous height, upon one another, the hairs that compose the lowermost Locks which support the rest, would, by the weight of all the Wool above them, be as well strongly compress'd, as if a Man should squeeze them together in his hands, or employ any such other moderate force to compress them. So that we need not wonder, that upon the taking off the incumbent Air from any parcel of the Atmosphere here below, the Corpuscles, whereof that undermost Air consists, should display themselves, and take up more room than before.

And if it be objected, That in Water, the weight of the upper and of the lower part is the same: I answer, That, (besides that it may be well doubted whether the observation, by reason of the great difficulty, hath been exactly made,) there is a manifest disparity betwixt the Air and Water: For I have not found, upon an Experiment purposely made, (and in another Treatise Recorded) that Water will suffer any considerable compression; whereas we may observe in Wind-Guns, (to mention now no other Engines) that the Air will suffer it self to be crouded into a comparatively very little room; in so much, that a very diligent Examiner of the Phaenomena of Wind-Guns would have us believe, that in one of them, by condensation, he reduc'd the Air into a space at least eight times narrower than it before possest. And to this, if we add a noble Phaenomenon of the Experiment De Vacuo; these things put together, may for the present suffice to countenance our Doctrine. For that noble Experimenter, Monsieur Pascal (the Son) had the commendable Curiosity to cause the Torricellian Experiment to be tri'd at the foot, about the middle, and at the top of that high Mountain (in Auvergne, if I mistake not) commonly call'd Le Puy de Domme; whereby it was found, That the Mercury in the Tube fell down lower, about three inches, at the top [Page] of the Mountain than at the bottom. And a Learned Man a while since inform'd me, That a great Virtuose, friend to us both, hath, with not unlike success, tried the same Experiment in the lower and upper parts of a Mountain in the west of England. Of which, the reason seems manifestly enough to be this, That upon the tops of high Mountains, the Air which bears against the restagnant Quick-silver, is less press'd by the less ponderous incumbent Air; and consequently is not able totally to hinder the descent of so tall and heavy a Cylinder of Quick-silver, as at the bottom of such Mountains did but maintain an AEquilibrium with the incumbent Atmosphere.

And if it be yet further Objected against what hath been propos'd touching the compactness and pressure of the inferiour Air; That we find this very Air to yield readily to the motion of little Flies, and even to that of Feathers, and such other light and weak Bodies; which seems to argue, that the particles of our Air are not so compress'd as we have represented them, especially, since by our former Experiment it appears, that the Air readily dilated it self downward, from the Receiver into the Pump, when 'tis plain, that it is not the incumbent Atmosphere, but only the subjacent Air in the brass Cylinder that hath been remov'd: If this, I say, be objected, we may reply, That, when a man squeezeth a fleece of Wool in his hand, he may feel that the Wool incessantly bears against his hand, as that which hinders the hairs it consists of, to recover their former and more natural extent. So each parcel of the Air about the Earth, doth constantly endeavour to thrust away all those contiguous Bodies, (whether. Aëreal or more gross,) that keep it bent, and hinder the expansion of its parts, which will dilate themselves, or fly abroad towards that part, (whether upwards or downwards,) where they find their attempted Dilatation of themselves less resisted by the neighbouring Bodies. Thus the Corpuscles of that Air we have been all this while speaking of, being unable, by reason of their weight, to ascend above the Convexity of the Atmosphere, and by reason [Page] of the resistance of the surface of the Earth and Water, to fall down lower, they are forced, by their own gravity and this resistance, to expand and diffuse themselves about the Terrestrial Globe; whereby it comes to pass, that they must as well press the contiguous Corpuscles of Air that on either side oppose their Dilatation, as they must press upon the surface of the Earth, and, as it were recoyling thence, endeavour to thrust away those upper particles of Air that lean upon them.

And, as for the easie yielding of the Air to the Bodies that move in it, if we consider that the Corpuscles whereof it consists, though of a springy nature, are yet so very small, as to make up (which 'tis manifest they do) a fluid Body, it will not be difficult to conceive, that in the Air, as in other Bodies that are fluid, the little Bodies it consists of, are in an almost restless motion, whereby they become (as we have more fully discoursed in another Treatise) In a Discourse touching fluidity and firmness. very much disposed to yield to other Bodies, or easie to be displac'd by them; and that the same Corpuscles are likewise so variously mov'd, as they are intire Corpuscles, that if some strive to push a Body plac'd among them towards the right hand (for instance) others, whose motion hath an opposite determination, as strongly thrust the same Body towards the left; whereby neither of them proves able to move it out of its place, the pressure on all hands being reduced as it were to an AEquilibrium: So that the Corpuscles of the Air must be as well sometimes considered under the notion of little Springs, which remaining bent, are in their entire bulk transported from place to place; as under the notion of Springs displaying themselves, whose parts fly abroad, whilst, as to their entire bulk they scarce change place: As the two ends of a Bow, shot off, fly from one another, whereas the Bow it self may be held fast in the Archer's hand; and that it is the equal pressure of the Air on all sides upon the Bodies that are in it, which causeth the easie Cession of its parts, may be argu'd from hence: That if by the help of our Engine the Air [Page] be but in great part, though not totally, drawn away from one side of a Body without being drawn away from the other, he that shall think to move that Body to and fro, as easily as before, will find himself much mistaken.

In verification of which we will, to divert your Lordship a little, mention here a Phaenomenon of our Engine, which even to divers ingenious persons hath at first sight seem'd very wonderfull.

EXPERIMENT II.

THe thing that is wont to be admired, and which may pass for our second experiment is this, That if, when the Receiver is almost empty, a By-stander be desired to lift up the brass Key (formerly described as a stopple in the brass Cover) he will find it a difficult thing to do so, if the Vessel be well exhausted; and even when but a moderate quantity of Air hath been drawn out, he will, when he hath lifted it up a little, so that it is somewhat loose from the sides of the lip or socket, which (with the help of a little oyl) it exactly filled before, he will (I say) find it so difficult to be lifted up, that he will imagine there is some great weight fastned to the bottom of it. And if (as sometimes hath been done for merriment) onely a Bladder be tied to it, it is pleasant to see how men will marvail that so light a Body, filled at most but with Air, should so forcibly draw down their hand as if it were fill'd with some very ponderous thing: Whereas the cause of this pretty Phaenomenon seems plainly enough to be only this, That the Air in the Receiver, being very much dilated, its Spring must be very much weakn'd, and consequently it can but faintly press up the lower end of the stopple, whereas the Spring of the external Air being no way debilitated, he that a little lifts up the stopple must with his hand support a pressure equal to the disproportion betwixt the force of the internal expanded Air, and that of the Atmosphere incumbent upon the upper part of the same key or stopple: And so men being unused to find any resistance, in lifting things up, [Page] from the free Air above them, they are forward to conclude that that which depresseth their hands must needs be some weight, though they know not where plac'd, drawing beneath it.

And, that we have not mis-assign'd the cause of this Phaenomenon, seems evident enough by this, That as Air is suffered by little and little to get into the Receiver, the weight that a man fancieth his hand supports, is manifestly felt to decrease more and more, the internal Air by this recruit approaching more to an AEquilibrium with the external, till at length the Receiver growing again full of Air, the stopple may be lifted up without any difficulty at all.

By several other of the Experiments afforded us by our Engine, the same notion of the great and equal pressure of the free Air upon the Bodies it environs, might be here manifested, but that we think it not so fit to anticipate such Experiments: And therefore shall rather employ a few lines to clear up the difficulty touching this matter, which we have observ'd to have troubled some even of the Philosophical and Mathematical Spectators of our Engine, who have wonder'd that we should talk of the Air exquisitely shut up in our Receiver, as if it were all one with the pressure of the Atmosphere; whereas the thick and close body of the Glass, wholly impervious to the Air, doth manifestly keep the incumbent Pillar of the Atmosphere from pressing in the least upon the Air within the Glass, which it can no where come to touch. To elucidate a little this matter, let us consider, That if a man should take a fleece of Wooll, and having first by compressing it in his hand reduc'd it into a narrower compass, should nimbly convey and shut it close up into a Box just fit for it, though the force of his hand would then no longer bend those numerous springy Bodies that compose the Fleece, yet they would continue as strongly bent as before, because, the Box they are inclos'd in, would as much resist their re-expanding of themselves, as did the hand that put them in. For thus we may conceive, that the [Page] Air being shut up, when its parts are bent by the whole weight of the incumbent Atmosphere, though that weight can no longer lean upon it, by reason it is kept off by the Glass, yet the Corpuscles of the Air within that Glass continue as forcibly bent, as they were before their inclusion, because the sides of the Glass hinder them from displaying or stretching out themselves. And if it be objected that this is unlikely, because even Glass bubbles, such as are wont to be blown at the flame of a Lamp, exceeding thin, and Hermetically seal'd, will not break; whereas it cannot be imagin'd that so thin a Prison of Glass could resist the Elastical force of all the included Air, if that Air were so compress'd as we suppose: It may be easily reply'd, That the pressure of the inward Air against the Glass, is countervail'd by the equal pressure of the outward against the same Glass. And we see in bubbles, that by reason of this, an exceeding thin film of Water is often able, for a good while, to hinder the eruption of a pretty quantity of Air. And this may be also more conspicuous in those great Spherical bubbles, that Boyes sometimes blow with Water, to which Sope hath given a Tenacity. But that, if the pressure of the ambient Air were remov'd, the internal Air may be able to break thicker Glasses, than those lately mention'd, will appear by some of the following Experiments; to which, we shall therefore now hasten, having, I fear, been but too prolix in this Excursion, though we thought it not amiss to annex to our first Experiments some general Considerations touching the Spring of the Air, because (this Doctrine being yet a stranger to the Schools) not only we find not the thing it self to be much taken notice of; but of those few that have heard of it, the greater part have been forward to reject it, upon a mistaken perswasion, that those Phaenomena are the effects of Natures abhorrency of a Vacuum, which seem to be more fitly ascribable to the weight and spring of the Air.

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EXPERIMENT III.

WE will now proceed to observe, that though, by the help of the handle, the Sucker be easily drawn down to the bottom of the Cylinder; yet, without the help of that Leaver, there would be required to the same effect, a force or weight great enough to surmount the pressure of the whole Atmosphere: since otherwise the Air would not be driven out of its place, when none is permitted to succeed into the place deserted by the Sucker. This seems evident, from the known Torricellian Experiment, in which, if the inverted Tube of Mercury be but 25 Digits high, or somewhat more, the Quicksilver will not fall, but remain suspended in the Tube, because it cannot press the subjacent Mercury with so great a force, as doth the incumbent Cylinder of the Air, reaching thence to the top of the Atmosphere: Whereas, if the Cylinder of Mercury were three or four digits longer, it would over-power that of the external Air, and run out into the Vessel'd Mercury, till the two Cylinders came to an AEquilibrium, and no further. Hence we need not wonder, that though the Sucker move easily enough up and down in the Cylinder by the help of the Manubrium; yet if the Manubrium be taken off, it will require a considerable strength to move it either way. Nor will it seem strange, that if, when the Valve and Stop-cock are well shut, you draw down the Sucker, and then let go the Manubrium; the Sucker will, as it were of it self, re-ascend to the top of the Cylinder, since the spring of the external Air findeth nothing to resist its pressing up the Sucker. And for the same reason, when the Receiver is almost evacuated, though, having drawn down the Sucker, you open the way from the Receiver to the Cylinder, and then intercept that way again by returning the Key; the Sucker will, upon the letting go the Manubrium, be forcibly carried up almost to the top of the Cylinder: Because the Air within the Cylinder, being equally dilated and weakned with that of the Glass, is unable to withstand [Page] the pressure of the external Air, till it be driven into so little space, that there is an AEquilibrium betwixt its force and that of the Air without. And congruously hereunto we find, that in this case, the Sucker is drawn down with little less difficulty, than if the Cylinder, being devoid of Air, the Stopcock were exactly shut: We might take notice of some other things, that depend upon the Fabrick of our Engine it self; but to shun prolixity, we will, in this place, content our selves to mention one of them, which seems to be of greater moment than the rest, and it is this; that when the Sucker hath been impell'd to the top of the Cylinder, and the Valve is so carefully stopp'd, that there is no Air left in the Cylinder above the Sucker: If then the Sucker be drawn to the lower part of the Cylinder, he that manageth the Pump findeth not any sensibly greater difficulty to depress the Sucker, when it is nearer the bottom of the Cylinder, than when it is much farther off. Which circumstance we therefore think fit to take notice of, because an eminent Modern Naturalist hath taught, that, when the Air is sucked out of a Body, the violence wherewith it is wont to rush into it again, as soon as it is allow'd to re-enter, proceeds mainly from this; That the pressure of the ambient Air is strengthened upon the accession of the Air suck'd out; which, to make it self room, forceth the neighbouring Air to a violent-subingression of its parts: which, if it were true, he that draweth down the Sucker, would find the resistance of the external Air increas'd as he draweth it lower, more of the displaced Air being thrust into it to compress it. But, by what hath been discours'd upon the first Experiment, it seems more probable, that without any such strengthening of the pressure of the outward Air, the taking quite away or the debilitating of the resistance from within, may suffice to produce the effects under consideration. But this will perhaps be illustrated by some or other of our future Experiments, and therefore shall be no longer insisted on here.

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EXPERIMENT IV.

HAving thus taken notice of some of the constant Phaenomena of our Engine it self, let us now proceed to the Experiments triable in it.

We took then a Lambs Bladder large, well dry'd, and very limber, and leaving in it about half as much Air as it could contain, we caus'd the neck of it to be strongly try'd, so that none of the included Air, though by pressure, could get out. This Bladder being convey'd into the Receiver, and the Cover luted on, the Pump was set on work, and after two or three exsuctions of the ambient Air (whereby the Spring of that which remain'd in the Glass was weaken'd) the Imprison'd Air began to swell in the Bladder, and, as more and more of the Air in the Receiver was, from time to time, drawn out; so did that in the Bladder more and more expand it self, and display the folds of the formerly flaccid Bladder: So that before we had exhausted the Receiver near so much as we could, the Bladder appear'd as full and stretched, as if it had been blown up with a Quill.

And that it may appear that this plumpness of the Bladder proceeded from the surmounting of the debilitated Spring of the ambient Air remaining in the Vessel, by the stronger Spring of the Air remaining in the Bladder; we return'd the Key of the Stopcock, and by degrees allow'd the external Air to return into the Receiver: Whereupon it happen'd, as was expected, that as the Air came in from without, the distended Air in the Bladder, was proportionably compress'd into a narrower room, and the sides of the Bladder grew flaccid, till the Receiver having re-admitted its wonted quantity of Air, the Bladder appear'd as full of wrinkles and cavities as before.

This Experiment is much of the same nature with that which was, some years ago, said to be made by that eminent Geometrician Monsieur Roberval, with a Carps Bladder empty'd and convey'd into a Tube, wherein the Experiment De Vacuo was afterwards try'd, which ingenious Experiment of his, justly deserveth the thanks of those that have been, or shall be solicitous to discover the nature of the Air.

[Page]But to return to our Experiment, we may take notice of this Circumstance in it, That after the Receiver hath been in some measure empty'd, the Bladder doth, at each exsuction, swell much more conspicuously than it did at any of the first Exsuctions; insomuch that towards the end of the pumping, not only a great fold or cavity in the surface of the Bladder may be made even, by the stretching of the inward self-expanding Air: But we have sometimes seen, upon the turning of the Key to let the ambient Air pass out of the Receiver into the Cylinder, we have seen (I say) the Air in the Bladder suddenly expand it self so much and so briskly, that it manifestly lifted up some light Bodies that lean'd upon it, and seem'd to lift up the Bladder it self.

Now because it hath, by very learned Men, been doubted, whether the swelling of the Bladder may not have proceeded (not from the Dilatation of the included Air,) but from the Texture of the Fibres, which, being wont to keep the Bladder extended when the Animal (to whom it belong'd) was alive, may be suppos'd in our Experiment to have return'd, like so many Springs to their wonted extent, upon the removal of the ambient Air that compress'd and bent them: Because this, I say, hath been doubted, we thought fit to make this further trial.

We let down into the Receiver with the fore-mentioned Bladder two other much smaller, and of the same kind of Animal; the one of these was not ty'd up at the neck that there might be liberty left to the Air that was not squeez'd out (which might amount to about a fifth part of what the Bladder held before) to pass out into the Receiver: The other had the sides of it stretch'd out and press'd together, almost into the form of a Cup, that they might intercept the less Air betwixt them, and then was strongly ty'd up at the neck: This done, and the Air being in some measure suck'd out of the Pneumatical Glass (if I may so call it) the Bladder, mention'd at the beginning of our Experiment, appear'd extended every way to its full Dimensions; whereas neither of the two others did remarkably swell, and that, whose neck was not ty'd, seem'd very little, if at all less wrinkl'd than when it was put in.

We made likewise a strong Ligature about the middle of a long [Page] Bladder partly empty'd, and upon the drawing the Air out of the Receiver, could observe no such swelling betwixt the Ligature and the neck of the Bladder, which had been purposely left open, as betwixt the same Ligature and the bottom of the Bladder, whence the included Air could no way get out.

But a farther and sufficient manifestation whence the intumescence of the Bladder proceeds, may be deduc'd from the following Experiment.

EXPERIMENT V.

TO try then at once both what it was that expanded the Bladder, and what a powerfull Spring there is ev'n in the Air we are wont to think uncompress'd: We caus'd a Bladder dry, well ty'd and blown moderately full, to be hung in the Receiver by one end of a string, whose other end was fastned to the inside of the Cover: and upon drawing out the ambient Air, that press'd on the Bladder; the internal Air not finding the wonted resistance, first swell'd and distended the Bladder, and then broke it, with so wide and crooked a rent, as if it had been forcibly torn asunder with hands. After which a second Bladder being convey'd in, the Experiment was repeated with like success: And I suppose it will not be imagin'd that in this case the Bladder was broken by its own Fibres, rather than by the Imprison'd Air.

And of this Experiment these two Phaenomena may be taken notice of: The one, that the Bladder at its breaking gave a great report, almost like a Cracker: And the other, That the Air contain'd in the Bladder, had the power to break it with the mention'd Impetuosity, long before the ambient Air was all, or near all, drawn out of the Receiver.

But, to verifie what we say in another Discourse, where we show, That even true Experiments may, by reason of the easie mistake of some unheeded Circumstance, be unsuccessfully try'd; we will Advertise, on this occasion, that we did oftentimes in vain try the breaking of Bladders, after the manner above mention'd: Of which the cause appear'd to be this, That the Bladders we could [Page] not break, having been brought us ready blown from those that sold them, were grown dry before they came to our hands: whence it came to pass, that, if we afterwards ty'd them very hard, they were apt to fret and so become unserviceable; and if we ty'd them but moderately hard, their stifness kept them from being clos'd so exactly, but that when the included Air had in the exhausted Receiver distended them as much as easily it could, it would in part get out between the little wrinkles of the Sphincter of the Neck: Whence also it usually happen'd, that, upon the letting in the Air from without, the Bladders appear'd more flaccid and empty than before they were put in; whereas when the Bladders were brought us moist from the Butchers, we could, without injuring them, tie their necks so close, that none of the Air once blown in, could get out of them, but by violently breaking them.

It would not be amiss on this occasion to point at something which may deserve a more deliberate Speculation than we can now afford it; namely that the Elastical Power of the same Quantity of Air may be as well encreas'd by the Agitation of the Aërial Particles (whether only moving them more swiftly and scattering them, or also extending or stretching them out, I determine not) within an every way inclosing and yet yielding Body; as display'd by the withdrawing of the Air that press'd it without. For we found that a Bladder, but moderately fill'd with Air and strongly ty'd, being a while held near the Fire, not only grew exceeding turgid and hard, but afterwards, being brought nearer to the Fire, suddenly broke with so loud and vehement a noise, as stony'd those that were by, and made us for a while after, almost deaf.

EXPERIMENT VI.

HAving thus seen that the Air hath an Elastical Power, we were next desirous to know in some measure how far a parcel of Air might by this its own Spring be dilated. And though we were not provided of Instruments fit to measure the dilatation of the Air any thing accurately, yet because an imperfect measure of it was more desirable than none at all, we devis'd the following method as very easily practicable.

[Page] We took a limber Lambs Bladder which was thorowly wetted in fair Water, that the sides of it being squeez'd together, there might be no Air left in its folds: (as indeed we could not afterwards upon trial discern any) The neck of this Bladder was strongly tied about that of a small Glass, (capable of holding five full drachmes of Water) the Bladder being first so compress'd, that all the included Air was only in the Glass, without being press'd there; then the Pump being set on work after a few exsuctions, the Air in the little Viol began to dilate it self and produce a small Tumor in the neck of the Bladder; and as the ambient Air was more and more drawn away, so the included Air penetrated farther and farther into the Bladder, and by degrees listed up the sides and display'd its folds, till at length it seem'd to have blown it up to its full extent: Whereupon the external Air, being permitted to flow back into the Receiver, repuls'd the Air that had fill'd the Bladder, into its former narrow receptacle, and brought the Bladder to be again flaccid and wrinkled as before: Then taking out the Bladder, but without severing it from the Glass, we did, by a hole made at the top of the Bladder, fill the Vessel, they both made up, with Water, whose weight was five Ounces five Drachmes and a half: Five Drachmes whereof were above-mention'd to be the contents of the Bottle. So that in this Experiment, when the Air had most extended the Bladder, it possess'd in all above nine times as much room as it did when it was put into the Receiver. And it would probably have much inlarg'd its bounds, but that the Bladder by its weight and the sticking together of its sides did somewhat resist its expansion: And which was more considerable, the Bladder appear'd tumid enough, whilst yet a pretty deal of Air was left in the Receiver, whose exsuction would according to our former Observation, probably have given way to a farther expansion of the Air, especially supposing the dilatation not to be restrain'd by the Bladder.

SInce we wrote the other day the former Experiment, we have met with some Glasses not very unfit for our purpose; by means of which we are now able, with a little more trouble, to [Page] measure the expansion of the Air a great deal more accurately than we could by the help of the above-mention'd Bladder, which was much too narrow to allow the Air its utmost distention.

We took then first a Cylindrical Pipe of Glass, whose bore was about a quarter of an Inch in Diameter: This Pipe was so bent and doubled, that, notwithstanding its being about two foot in length, it might have been shut up into a smaller Receiver, not a Foot high: But by misfortune it crack'd in the cooling, whereby we were reduced to make use of one part which was straight and intire, but exceeded not six or seven Inches. This little Tube was open at one end; and at the other, where it was Hermetically seal'd, had a small Glass bubble to receive the Air whose dilatation was to be measur'd.

Along the side of this Tube was pasted a straight narrow piece of Parchment, divided into twenty six equal parts, marked with black Lines and Figures, that by them might be measur'd both the included Air and its dilatation. Afterwards we fill'd the Tube with Water, almost to the top; and stopping the open end with the Finger, and inverting the Tube, the Air was permitted to ascend to the above mention'd Glass bubble. And by reason this ascent was very slow, it gave us the opportunity to mark how much more or less than one of the twenty six divisions this Air took up. By this means, after a trial or two, we were inabled to convey to the top of the Glass a bubble of Air equal enough, as to sight, to one of those Divisions: Then the open end of the Tube being put into a small Viol, whose bottom was cover'd with Water, about half an Inch high; we included both Glasses into a small and slender Receiver, and caused the Pump to be set on work. The event was, That at the first exsuction of the Air there appear'd not any expansion of the bubble, comparable to what appear'd at the second, and that upon a very few exsuctions the bubble reaching as low as the surface of the subjacent Water, gave us cause to think, That if our Pipe had not been broken, it would have expanded it self much farther: Wherefore we took out the little Tube, and found that besides the twenty six divisions formerly mention'd, the Glass bubble and some part of the Pipe [Page] to which the divided Parchment did not reach, amounted to six divisions more. Whereby it appears that the Air hath take up one and thirty times as much room as before, and yet seem'd capable of a much greater expansion, if the Glass would have permitted it. Wherefore after the former manner, we let in another bubble, that by our guess was but half as big as the former, and found, that upon the exsuction of the Air from the Receiver, this little bubble did not only fill up the whole Tube, but (in part) break through the subjacent Water in the Viol, and thereby manifest it self to have prossessed sixty and odd times its former room.

These two Experiments are mention'd to make way for the more easy belief of that which is now to follow. Finding then that our Tube was too short to serve our turn, we took a slender Quill of Glass which happen'd to be at hand, though it were not so fit for our purpose as we could have wished, in regard it was three or four times as big at one end as the other. This Pipe which was thirty Inches long, being Hermetically seal'd at the slender end, was almost filled with water; and after the above-related manner a bubble was convey'd to the top of it, and the open extreme was put into a Viol that had a little fair Water at the bottom: Then the Cover, by means of a small hole purposely made in it for the Glass Pipe to stand out at, was cemented on to the Receiver, and the Pump being set on work, after some exsuctions, not only the Air manifestly appear'd extended below the surface of the subjacent Water; but one of the By-standers affirms, that he saw some bubbles come out at the bottom of the Pipe and break through the Water. This done, we left off Pumping, and observ'd how at the unperceiv'd leaks of the Receiver the Air got in so fast, that it very quickly impell'd up the Water to the top of the Tube, excepting a little space whereinto that bubble was repuls'd, which had so lately possess'd the whole Tube; this Air at the slender end appear'd to be a Cylinder of ⅚ parts of an Inch in length, but when the Pipe was taken out and turn'd upside down, it appear'd at the other end inferiour in bulck to a Pea.

These things being thus done we took (to make the Experiment [Page] the more exactly) a small pair of Scales, such as Gold-Smiths use to weigh Cold Coyn in; and weighing the Tube and Water in it, we found them to amount to one Ounce thirty Grains and an half: Then we pour'd in as much Water as serv'd to fill up the Tube, wherein before we had left as much space unfill'd up as was possess'd by the bubble, and weighing again the Pipe and Water, we found the weight increas'd onely by one Grain. Lastly, pouring out the Water, and carefully freeing the Pipe from it (which yet we could not perfectly doe) we weighed the Glass alone, and found it to want two Drachmes and thirty two Grains of its former weight: So that the bubble of Air taking up the room but of one Grain in weight of Water, it appear'd that the Air by its own [...] was so rarified, as to take up one hundred fifty two times as much room as it did before: Though it were then compress'd by nothing but the ordinary pressure of the contiguous Air. I know not whether it be requisite to take notice, that this Experiment was made indeed in a moist Night, but in a Room, in whose Chimney there was burning a good Fire, which did perhaps somewhat rarifie the Air of which the bubble consisted.

It hath seem'd almost incredible which is related by the Industrious Mersennus, That the Air by the violence of heat, though as great as our Vessels can support without fusion, can be so dilated as to take up seventy times as much room as before: Wherefore because we were willing to have a confirmation of so strange a Phaenomenon; we once more convey'd into the Tube a bubble of the bigness of the former, and prosecuting the Experiment as before with the same Water, we observed that the Air did manifestly stretch it self so far, as to appear several times a good way below the surface of the Water in the Viol, and that too with a surface very convex toward the bottom of the Pipe. Nay, the Pump being ply'd a little longer, the Air did manifestly reach to that place where the bottom of the Tube leaned upon the bottom of the Viol, and seemed to knock upon it and rebound from it: Which Circumstances we add, partly that the Phaenomenon we have been relating may not be imputed to the bare subsiding of the Water that filled the Tube, upon the taking off the pressure of the ambient [Page] Air. And partly also that it may appear that if our Experiments have not been so accurately made as with fitter Instruments might perhaps be possible; yet the expansion of the Air is likely to be rather greater than lesser than we have made it: Since the Air was able to press away the Water at the bottom of the Pipe, though that were about two Inches below the surface of the Water that was then in the Viol, and would have been at least as high in the Pipe, if the Water had onely subsided and not been depressed: So that it seems not unlikely that if the Experiment could be so made, as that the expansion of the Air might not be resisted by the Neighbouring Bodies, it would yet enlarge its bounds, and perhaps stretch it self to two hundred times its former bulk, if not more. However, what we have now tryed will, I hope, suffice to hinder divers of the Phaenomena of our Engine from being distrusted: Since in that part of the Atmosphere we live in, that which we call the free Air (and presume to be so uncompressed) is crouded into so very small a part of that space, which if it were not hindred it would possess. We would gladly have tryed also whether the Air at its greatest expansion could be farther rarified by heat; but doe what we could, our Receiver leaked too fast to let us give our selves any satisfaction in that particular.

EXPERIMENT VII.

TO discover likewise by the means of that pressure of the Air, both the strength of Glass, and how much interest the Figure of a Body may have in its greater or lesser Resistance to the pressure of other Bodies, we made these farther tryals.

We caus'd to be blown with a Lamp, a round Glass bubble, capable of containing, by guess, about five Ounces of Water, with a slender neck about the bigness of a Swan's Quill, and it was purposely blown very thin, as Viols made with Lamps are wont to be, that the thinness of the matter might keep the roundness of the Figure from making the Vessel too strong. Then having moderately emptied the Receiver, and taken it out of the Pump, we speedily applied to the Orifice of the bottom [Page] of it, the Neck of the newly mention'd Glass, carefully stopping the Crannies with melted Plaister, that no Air might get in at them: And after turning the Key of the Stop-cock, we made a free passage for the Air to pass out of the bubble into the Receiver: Which it did with great celerity, leaving the bubble as empty as the Receiver it self; as appear'd to us by some Circumstances not now to be insisted on. Notwithstanding all which, the Vessel, continuing as intire as before, gave us cause to wonder that the bare roundness of the Figure should enable a Glass, almost as thin as Paper, to resist so great a pressure as that of the whole incumbent Atmosphere. And having reiterated the Experiment, we found again that the pressure of the ambient Body, thrusting all the parts inwards, made them, by reason of their arched Figure, so support one another, that the Glass remain'd as whole as at first.

Now that the Figure of the Glass is of great moment in this matter, may be evinced by this other Experiment.

EXPERIMENT VIII.

WE took a Glass Helmet or Alembick (delineated by the seventh Figure) such as Chymists use in Distillations, and containing by conjecture between two and three Pints: The Rostrum or Rose of it mark'd with (c) was Hermetically closed; and at the top of it was a hole, into which was fitted and cemented one of the Shanks of a middle-siz'd Stop-cock; so that the Glass being turn'd upside-down, the wide Orifice (which in common Glass-Helmets is the onely one) was upwards; and to that wide Orifice was fitted a cast cover of Lead, which was carefully cemented on to the Glass: Then the other Shank of the Stop-cock being with cement likewise fasten'd into the upper part of the Pump, the exsuction of the Air was endeavoured. But it was not long before, the remaining Air being made much too weak to ballance the pressure of the Ambient Air, the Glass was (not without a great noise) crack'd almost half round, along that part of it where it began to bend inwards: As if in the Figure, the crack had been made according to the Line (a b,) and [Page] upon an endeavour to pump out more of the Air, the crack once begun, appear'd to run on farther; though the Glass where it was broken seem'd to be (by conjecture) above ten, some thought above twenty times, as thick as the bubble mentioned in the foregoing Experiment.

This will perhaps make it seem strange, that having taken another Glass bubble blown at the same time, and like for ought we discerned for size, thickness and Figure, to that thin one formerly mentioned; and having sealed it up Hermetically, and suspended it in the Receiver, the exsuction of the ambient Air did not enable the imprisoned Air to break, or in the least to crack the bubble; though the Experiment were laboriously tried, and that several times with bubbles of other sizes: But that perhaps the heat of the Candle or Lamp wherewith such Glasses are Hermetically sealed, (not to mention the warmth of his hands that seal'd it) might so rarefy the contained Air, as much to weaken its Spring, may seem probably by the following Experiments.

EXPERIMENT IX.

WE took a Glass Viol able to hold three or four Ounces of Water, and of the thickness usual in Glasses of that size; into the Neck of this was put a moderately slender Pipe of Glass, which was carefully fastened with a mixture of equal parts of Pitch and Rosin to the Neck of the Viol, and which reached almost to the bottom of it, as the sixth Figure declareth.

This Viol being, upon a particular design, filled with Water, till that came up in it, a pretty deal higher than the lower end of the Pipe, was put into one of our small Receivers, (containing between a Pint and a Quart) in such manner as that the Glass Pipe, passing through a hole made purposely for it in the Leaden-Cover of the Receiver, was for the most part of it without the Vessel, which being exactly closed, the Pump was set on work: But at the very first exsuction, and before the Sucker was drawn to the bottom of the Cylinder, there flew out of the Viol a piece of Glass half as broad as the Palm of a Man's Hand, and it was [Page] thrown out with such violence, that hitting against the Neighbouring side of the Receiver, it not onely dashed it self to pieces, but cracked the very Receiver in many places, with a great noise that much surprised all that were in the Room. but it seemed, that in so little a Receiver, the Air about the Viol being suddenly drawn out, the Air imprisoned in the Vessel, having on it the whole pressure of the Atmosphere (to which by the Pipe open at both ends, It and the Water were exposed) and not having on the other side the wonted pressure of the Ambient Air to ballance that other pressure, the resistance of Glass was finally surmounted, and the Viol once beginning to break where it was weakest, the external Air might rush in with violence enough to throw the cracked parcel so forcibly against the Neighbouring side of the Receiver, as to break that too.

And this may be presumed sufficient to verify what we delivered in that part of our Appendix to the first Experiment where we mentioned the almost equal pressure of the Air on either side of a thin Glass Vessel, as the cause of its not being broken by the forcible spring of the contained Air. But yet that it be not suspected that chance had an interest in so odd an Experiment as we have been relating, we will add that for farther satisfaction we reiterated it in a round Glass containing by Guess about six ounces of Water: This Viol we put into such a small Receiver as was lately mentioned, in such manner as that the bottom of it rested upon the lower part of the Pneumatical Glass, and the Neck came out through the Leaden-cover of the same at a hole made purposely for it. But being made circumspect by the foregoing mischance, we had put the Viol into a Bladder, before we put it into the Receiver to hinder this last-named Glass from being endangered by the breaking of the other. Then the Pneumatical Vessel being closed so that no way was left for the outward Air to get into it, but by breaking through the Viol, into whose cavity it had free access by the mouth of it, (which was purposely left open,) the Sucker being nimbly drawn down, the [Page] external Air immediately pressed forcibly as well upon the Leaden-cover as the Viol; and the Cover happening to be in one place a little narrower than the edge of the Pneumatical Glass, was depressed, and thrust into it so violently by the incumbent Air, that getting a little within the tapering Lip of the Glass, it did (like a kind of Wedge,) thrust out that side where it was depressed, so as, (though the Receiver was new,) to split it. This accident being thus mentioned upon the bye to confirm what we formerly said touching the fitness or unfitness of Glasses of some Figures to resist the pressure of the Atmosphere; We will proceed to relate the remaining part of the Experiment, namely, That having fitted on a wider Cover to the same Receiver, and closed both that and the crack with Cement, we prosecuted the Experiment in the manner above related, with this success: That upon the quick depressing of the Sucker, the external Air burst the Body of the Viol into above an hundred pieces, many of them exceeding small, and that with such violence, that we found a wide rent, besides many holes, made in the Bladder it self.

And to evince that these Phaenomena were the effects of a limited and even moderate force, and not of such an abhorrency of a Vacuum as that to avoid it, many have been pleased to think that Nature must, upon occasion, exercise an almost boundless power; we afterwards purposely try'd this Experiment with several Glasses somewhat thicker than those Viols, and found the event to verify our conjecture, that it would not succeed: For the Glasses were taken out as intire as they were put in.

And here, My Lord, I hold it not unfit, upon occasion of the mention that hath been made of our having employ'd small Receivers, and one of them, notwithstanding its being crack'd, to annex these two Advertisements.

First then, besides the great Pneumatical Glass so often mentioned, and the proportionate Stop-cock, we thought fit to provide our selves with some small Receivers blown of Crystalline Glass, of several Shapes, and furnished with smaller Stop-cocks purposely made; and this we did upon hopes, that [Page] when we had surmounted the difficulties to be met with in Cementing the Glasses to the Stop-cocks, and the Pneumatical Vessels to the Pump, so exquisitely as is requisite for our purpose, we should from the smallness of our Receivers receive a four-fold Advantage. The first, that by reason of the slenderness of the Vessels, and their being made of much purer and clearer metal, (as the Glass-men speak,) than the great Receiver, we might have a more perfect view of every thing happening within them. The next, that such small Vessels might be emptied with less labour and in much less time. The third, that this nimble exsuction of the ambient Air would make many changes in the Bodies shut up in these Glasses more sudden and conspicuous than otherwise they would prove. And the last, that we should be able to draw and keep out the Air much more perfectly from such small Vessels than from our large Receiver, But though we were not much disappointed in the expectation of the three first advantages, yet we were in our hopes of the fourth. For besides the great difficulty we found in fitting together the Glasses, the Stop-cocks, and the Covers; besides this I say, we found our selves seldom able to draw, and keep out the Air so far as to make the remaining Air in these Receivers weaker than the remaining Air in our great Receiver. For though sometimes the Leaks of some of these little Receivers may be much (either fewer or smaller) than those of the larger Vessel; yet a little Air getting into one of these, wherein it had but little room to expand and display it self, might press as much upon all parts of the internal surface of the Vessel, and upon the included Bodies, as a greater quantity of the Air in a Vessel in whose capacity it might find more room to expand it self.

The other thing that we were to advertise, is, That 'tis not every small crack that can make such a Receiver as is of a roundish Figure altogether useless to our Experiment, in regard that upon the exsuction of the internal Air, the ambient Air on all sides pressing the Glass inwards or towards the middle, doth consequently thrust the Lips of the crack closer, and so rather close than increase it.

[Page]This I mention partly because Receivers fit for our turn are more easily cracked than procured, and therefore ought not to be unnecessarily thrown away as unserviceable: And partly because I think it becomes one that professeth himself a faithfull Relator of Experiments, not to conceal from Your Lordship, that after a few of the foregoing Experiments were made, there happened in the great Receiver a crack of about a Span long, beginning at the upper Orifice, and occasion'd, as it seem'd, by the excessive heat of too large an Iron that was employ'd to melt the Cement about that Orifice. But having laid upon this crack a broad Plaister, (which in one of our Essays written some years since to your ingenious and hopefull Cousin Jones, we extoll for the mending of crack'd Receivers, and other Chymical Glasses;) and having afterwards thickly overlaid this Plaister with Diachylon, we neither could then, nor can yet perceive that the Vessel leaks sensibly at that crack.

The Plaister was made of good quick Lime finely poudred, and nimbly ground with a Pestle in a Mortar, with a quantity (I know not how much precisely, not having those Essays in this place) of scrapings of Cheese and a little fair Water, no more than is just necessary to bring the mixture to a somewhat soft Paste, which when the Ingredients are exquisitely incorporated, will have a strong and stincking smell: Then it must be immediately spread upon a Linnen Cloath of three or four fingers breadth, and presently apply'd, lest it begin to harden. But if your Lordship had seen how we mended with it Receivers even for the most subtle Chymical Spirits. You would scarce wonder at the service it hath done in our Pneumatical Glass.

EXPERIMENT X.

WE took a Tallow-candle of such a size that eight of them make about a pound, and having in a very commodious Candlestick let it down into the Receiver, and so suspended it, that the Flame burnt almost in the middle of the Vessel, we did in some two minutes exactly close it up: and upon pumping very nimbly, we found, that, within little more than half a minute [Page] after, the Flame went out, though the Snuff had been purposely left of that length we judged the most convenient for the lasting of the Flame.

But the second time having put in the same Candle into the Receiver, (after it had by the blasts of a pair of Bellows been freed from Fumes) the Flame lasted about two minutes from the time the Pumper began to draw out the Air; upon the first exsuction whereof, the Flame seem'd to contract it self in all its dimensions. And these things were farther observable, that after the two or three first exsuctions of the Air, the Flame (except at the very top) appear'd exceeding blew, and that the Flame still receded more and more from the Tallow, till at length it appear'd to posses onely the very top of the Week, and there it went out.

The same Candle being lighted again was shut into the Receiver, to try how it would last there without drawing forth the Air, and we found that it lasted much longer than formerly; and before it went out, receded from the Tallow towards the top of the Week, but not neer so much as in the former Experiment.

And having an intention to observe particularly what the motion of the Smoke would be in these Experiments: We took notice that when the Air was not drawn out, there did, upon the extinction of the Flame, a considerable part of the Week remain kindled, which (probably by reason of the Circulation of the Air) in the Vessel, occasion'd by the heat) emitted a Steam, which ascended swiftly and directly upwards in a slender and uninterrupted Cylinder of smoke, till it came to the top, whence it manifestly recoil'd by the sides to the lower part of the Vessel. Whereas when the Flame went out upon the exsuction of the Air one time (when the Flame retir'd very leasurely to the top) we perceived it not to be follow'd by any smoke at all. And at another time the upper part of the Week remaining kindled after the extinction of the Flame, the slender steam of Fumes that did arise ascended but a very little way, and then after some uncertain motions this and that way, did, for the most part, soon fall downwards.

[Page]Being desirous also to try whether there would be any difference as well in our Receiver, as there is wont to be elsewhere betwixt Candles made of Wax and those made of Tallow, as to their duration; we took slender Tapers of white Wax, (commonly called Virgins Wax) that being found to burn with much less smoke than common yellow Wax. Six of these of like bigness, and each of them of about the thickness of a Swan's Quill, we press'd together into one Candle: and having lighted all the Weeks, we let in the above-mention'd Wax-candle into the Receiver, and made what haste we could to close it up with Cement. But, though in the mean while we left open the Valve of the Cylinder, the hole of the Stop-cock, and that in the Cover of the Receiver, that some Air might get in to cherish the Flame, and the Smoke might have a vent; Yet for so great a Flame the Air sufficed not so much as till the Cover could be perfectly luted on: So that before we were quite ready to imploy the Pump, the Candle was extinguished. Wherefore we took but one of the above mention'd Tapers, and having lighted it, clos'd it up in the Receiver, to try how long a small Flame with a proportionable smoke would continue in such a quantity of Air: but we found upon two several tryals, that from the beginning of pumping, the Flame went out in about a minute of an hour. It appear'd indeed to us that the swinging of the Wier to and fro (in the Engine shaken by pumping) hasten'd the vanishing of the Flame, which seem'd by that motion to be cast sometimes on one side of the Week and sometimes on the other. But though once we purposely refrain'd pumping after a very few exsuctions of the Air, that the Flame might not be agitated, yet it lasted not much longer than the newly-mention'd time. And lastly, closing up the same Taper, lighted again, to discover how long it would last without drawing out of the Air, we found that it burnt for a while vividly enough, but afterwards began to be lessen'd more and more in all its dimensions. And we observ'd that the Flame did not, as before, retire it self by little and little towards the top, but towards the bottom of the Week (from which yet it did a little withdraw upwards just before it went out) [Page] so that the upper part of the Week-appear'd for a pretty while manifestly above the top of the Flame, which having lasted about five minutes, was succeeded by a directly ascending stream of Smoke.

EXPERIMENT XI.

THere was taken a Wier, which being bent almost in the form of a Screw, constituted such an Instrument, to contain Coals and leave them every way accessible to the Air, as the tenth Figure declareth; the breadth of this Vessel was no less than that it might with ease be convey'd into the Receiver: And having fill'd it to the height of about five Inches with throughly kindled Wood-coals, we let it down into the Glass; and speedily closing it, we caus'd the Pumper to ply his work, and observ'd that upon the very first exsuction of the Air (though perhaps not because of that onely) the Fire in the Coals began to grow very dim, and though the agitation of the Vessel did make them swing up and down (which in the sree Air would have retarded the extinction of the Fire) yet when we could no longer discern any redness at all in any of them, casting our eyes upon a minute Watch we kept by us on this occasion, we found that from the beginning of the Pumping (which might be about two minutes after the Coals had been put in glowing) to the total dis-appearing of the Fire, there had passed but three minutes.

Whereupon, to try the Experiment a little farther, we presently took out the Coals, in which it seems there had remained some little parcels of Fire, rather cover'd than totally quench'd: For in the open Air the Coals began to be re-kindled in several places, wherefore having by swinging them about in the Wier, throughly lighted them the second time, we let them down again into the Receiver, and clos'd it speedily as before; and then waiting till the Fire seem'd totally extinct without medling with the Pump, we found that from the time the Vessel was clos'd, till that no Fire at all could be perceiv'd, there had passed about four minutes: Whereby it seem'd to appear that the [Page] drawing away of the ambient Air made the Fire go out sooner than otherwise it would have done; though that part of the Air that we drew out left the more room for the stifling steams of the Coals to be received into.

Lastly, Having taken out the Wier and put other Coals into it, we did, in the same Room where the Engine stood, let it hang quietly by a string in the open Air, to try how long the Fire would last without agitation, when no Air was kept from it, And we found that the Fire began to go out first at the top and outsides of the Coals; but inwards and near the bottom the Fire continu'd visible for above half an hour, a great part of the Coals, especially those next the bottom, being burnt to ashes before the Fire went out.

We caus'd likewise a piece of Iron to be forg'd, of the bigness of a middle siz'd Char-coal, and having made it red-hot throughout; we caus'd it in the lately mention'd Wier, to be speedily convey'd and shut up into the Receiver, being desirous to try what would become of a glowing Body, by reason of its texture more vehemently hot than a burning Coal of the same bigness, and yet unlike to send forth such copious and stifling Fumes: But we could not observe any manifest change upon the exsuction of the Air. The Iron began indeed to lose its fiery redness at the top, but that seem'd to be because it was at the upper end somewhat more slender than at the lower: The redness, though it were in the day time, continued visible about four minutes; and then, before it did quite disappear, we turn'd the Key of the Stop-cock, but could not discern any change of the Iron upon the rushing in of the Air. Yet some little remainders of Wax that stuck to the Wier, and were turn'd into Fumes by the heat of the neighbouring Iron, seem'd to afford a more plentifull, or at least a much more expanded Smoke when the Air was suck'd out, than afterwards; though allowance was made for the decreasing heat of the Iron. And lastly, notwithstanding a considerable exsuction of the ambient Air, though not by far so great a one as might have been made by the Engine; and notwithstanding the inconsiderable dissipation of the parts of the [Page] Iron; the surrounding sides of the Receiver were sensibly, and almost offensively heated by it; insomuch that a pretty while after the Iron was taken out, the sides of the Glass manifestly retain'd a warmth: which would not be unfit to be consider'd by a Person at more leasure than I am now.

EXPERIMENT XII.

BEing willing to try after this something that would not cherish much Fire at once, and would keep Fire much longer than a Coal: We took a piece of Match, such as Souldiers use, of the thickness of a Man's little Finger, or somewhat thicker; and this being well lighted at one end, was by a string suspended with that end downwards in the cavity of the Receiver which was immediately clos'd: And yet by that time it could well be so, the copious Fumes of the Match had near fill'd and darken'd the Receiver. Wherefore, lest the Vessel should be endanger'd, the Pump was nimbly ply'd, and a great deal of Air and Smoke mixt together was drawn out, whereby the Receiver growing more clear, we could discern the Fire in the Match to burn more and more languidly: and notwithstanding that by the diligence us'd in pumping, it seem'd to have room enough allow'd it to throw out Fumes; yet, after no long time, it ceas'd from being discernable either by its Light or its Smoke. And, though by that we were invited to suppose it quite extinguished, yet we continu'd pumping a-while, in prosecution of another Experiment we were trying at the same time: And this we did the more willingly, because of a suspicion, the Experiment about the Coals, might easily suggest, and which the event declar'd not to have been altogether groundless. For upon the admission of the external Air, the Fire, that seem'd to have gone out a pretty while before, did presently revive; and being as it were refresh'd by the new Air, and blown by the Wind made by that Air in rushing in, it began again to shine and dissipate the neighbouring Fuel into Smoke as formally.

[Page]

EXPERIMENT XIII.

A While after we let down into the Receiver together with a lighted piece of Match, a great Bladder well tyed at the Neck, but very lank, as not containing actually much (if any thing) above a Pint of Air, but being capable of containing ten or twelve times as much.

Our scope in this Experiment was partly to try whether or no the smoke of the Match, replenishing the Receiver, would be able to hinder the dilatation of the inward Air, upon the exsuction of the ambient: And partly to discover whether the extinction of the Fire in the Match did proceed from want of Air, or barely from the pressure of its own Fumes, which for want of room to expand themselves in, might be suppos'd to recoyl upon the Fire, and so to stifle it.

The event of our tryal was, That at the beginning of our pumping the Match appear'd well lighted, though it had almost fill'd the Receiver with its plentifull Fumes: But by degrees it burnt more and more dimly, notwithstanding, that by the nimble drawing out the Air and Smoke, the Vessel were made less opacous, and less full of compressing matter; as appear'd by this, That the longer we pump'd, the less Air and Smoke came out of the Cylinder at the opening of the Valve, and consequently the less came into it before; yet the Fire in the Match went but slowly out. And when afterwards, to satisfy our selves of its expiration, we had darken'd the Room, and in vain endeavoured to discover any spark of Fire, (as we could not for some time before by the help of Candles discern the least rising of Smoke,) we yet continued pumping six or seven times; and after all that, letting in the Air, the seemingly dead Fire quickly revived, and manifested its recovery by Light and store of Smoke, with the latter of which it quickly began to replenish the Receiver. Then we fell to pumping afresh, and continued that labour so long, till the re kindled Match went out again: and thinking it then fit not to cease from pumping so soon as before, we found that in less than half a quarter of an hour the [Page] Fire was got out for good and all, and past the possibility of being recover'd by the re-admitted Air.

Some Circumstances, besides those already mention'd, occurr'd in the making of the Experiment, of which these are the principal.

First, When the Receiver was full of Smoke, if the Cylinder were emptied, immediately upon the turning of the Stop-cock, the Receiver would appear manifestly darken'd to his eye that look'd upon the light through it: and this darkness was much less when the Receiver was much less fill'd with Fumes: It was also instantaneous, and seem'd to proceed from a sudden change of place and situation in the exhalations, upon the vent suddenly afforded them and the Air they were mixt with, out of the Receiver into the Cylinder.

The next thing we observed was, a kind of Halo that appear'd a good while about the Fire, and seem'd to be produced by the surrounding Exhalations.

And lastly, it is remarkable, That even when the Fumes seemed most to replenish the Receiver, they did not sensibly hinder the Air included in the Bladder from dilating it self after the same manner (for ought we could discern) as it would have otherwise done: So that before the Fire or the Match was quite extinct, the Bladder appear'd swell'd at least to six or seven times its former capacity.

Since the writing of these last Lines, we took a small Receiver, capable of containing (by guess) about a pound and a half of Water; and in the midst of it we suspended a lighted Match, but though within one minute of an hour (or there abouts) from the putting in of the Match, we had cemented on the Cover, yet we could not make such haste, but that before we began to pump, the Smoke had so fill'd that small Receiver, as for ought we discern'd, to choke the Fire. And having again and again reiterated the Experiment, it seem'd still as at first, that we could not close up the Vessel, and pump out all the Fumes time enough to rescue the Fire from extinction, whereupon we made use of this Expedient: Assoon as we had [Page] pump'd once or twice, we suddenly turn'd the Key, and thereby gave access to the excluded Air, which rushing violently in, as if it had been forced thorow a pair of Bellows, did both drive away the ashes, fill the Glass with fresh Air, and by blowing the almost extinguish'd Fire, re-kindl'd it, as appear'd by the Matches beginning again to smoke, which before it had ceas'd to do; we having by this means obtained a lighted Match in the Receiver, without being reduced to spend time to close it up, commanded the Air to be immediately pump'd out, and found that upon the exsuction of it, the Match quickly left smoking, as it seem'd, by reason of the absence of the Air; and yet if some urgent occasions had not hinder'd us, we would for greater security have try'd, whether or no the Match rekindled as formerly, would smoke much longer, in case of no exsuction of the ambient Air.

EXPERIMENT XIV.

TO try diverse things at once, and particularly whether Fire, though we found it would not long last, might not be produced in our evacuated Receiver: We took a Pistol of about a foot in length, and having firmly tyed it to a stick almost as long as the Cavity of the Receiver, we very carefully prim'd it with well dry'd Gunpowder, and then cocking it, we ty'd to the Tricker, one end of a string, whose other end was fasten'd to the Key formerly mention'd to belong to the Cover of our Receiver. This done, we convey'd the Pistol, together with the annexed Staff, into the Vessel which being clos'd up, and empty'd aster the usual manner, we began to turn the Key in the Cover; and thereby shortning the string that reach'd from it to the Pistol, we pull'd aside the Tricker, and observ'd, that according to our expectation the force of the Spring of the Lock was not sensibly abated by the absence of the Air: (from whose impetus yet some Modern Naturalists would derive the cause of the motion of Restitution in solid Bodies) For the Cock falling with its wonted violence upon the Steel, struck out of it as many, and as conspicuous parts of Fire, as, for ought we could [Page] perceive, it would have done in the open Air. Repeating this Experiment diverse times, we also observed whether or no there would appear any considerable diversity in the Motion of the shining Sparks in a place where the remaining Air was so much rarefied, but could not perceive but that they moved some of them upwards, as well as some of them downwards, and some of them side-ways, as they are wont to do, when upon such collisions they fly out in the open Air.

We likewise caus'd a piece of Steel to be made of the form and bigness of the Flint, in whose place we put it, and then the Pistol being cock'd and conveyed into the Receiver, the Tricker was pull'd after the Air was drawn out: And though the place were purposely somewhat darken'd, yet there appear'd not upon the striking of the two Steels against each other the least spark of Fire: Nor did we expect any (having before in vain attempted to strike Fire this way in the open Air) though we thought fit to make the Experiment, to undeceive those who fancy in rarefied Air, I know not what strange disposition, to take fire upon a much slighter occasion than this Experiment afforded. We have indeed found, that by the dextrous Collision of two harden'd pieces of Steel, store of sparks may be struck out: But that was done with such vehement percussion of the edges of the two Steels, as could not well be compass'd in our Receiver.

But the chief thing we design'd to doe with our Pistol, was, To observe whether Gun-powder would take Fire in our empty'd and closely stop'd Glass? Whether the expansion of the Flame would be considerably varied by the absence of so much of the ambient Air as was drawn out of the Receiver? And whether the Flame would diffuse it self upward, as it is wont, notwithstanding its not having about it the usual proportion of Air to force it up? And though most of our Attempts to fire the Gun-powder in the Pan of the Pistol succeeded not, because we were fain to let it hang almost perpendicular in the Receiver, whereby the Powder was shaken down before the sparks could reach it: yet once the Experiment succeeded, and the kindled Powder [Page] seem'd to make a more expanded Flame than it would have done in the open Air, but mounted upwards according to its wont, whether by reason of that little portion of Air, which in spight of our pumping remained in the Receiver, or for any other cause, we have not now the leasure to consider. But we must not forget, that upon the extinction of the Flame the Receiver appear'd darken'd with smoke, which seem'd to move freely up and down, and upon the letting in the Air at the Stop-cock began to circulate much [...]aster than before. We would have made more observations concerning this Flame, but that of two or three attempts we afterwards made to repeat the kindling of the Powder, not any one succeeded; and we have not the leasure to dwell long upon one kind of Trials.

EXPERIMENT XV.

TO these Experiments concerning Fire we added another, which though it succeeded not, may perhaps without impertinency be recorded: partly, because that (as we have in another Treatise amply declar'd) it is usefull to recite what Experiments miscarry as well as succeed. And partly also, because it is very possible that what we endeavoured in vain, may be performed by Your Lordship, or some other Vertuoso that shall have stancher Tessels than we had, and more Sunny days than the present Winter allows us.

We convey'd then into one of our small Receivers a piece of matter combustible, dry and black (experience declaring things of that colour to be most easily kindled) and carefully closing the Vessel, we brought it to a Window at which the Sun, not very far from the Meridian, shone in very freely: then drawing out the Air with speed we united the Sun beams with a Burning-glass upon the combustible matter, which began immediately to send forth a smoke that quickly darkned the Receiver, but notwithstanding all our care and diligence the external Air got in so fast, that after divers trials we were fain to leave off the Experiment in that Glass, and induc'd to make trial of it in our great Receiver.

[Page]Having then after some difficulty lodg'd the combustible matter in the cavity of this Vessel in such manner, as that it was almost contiguous to that side thereof that was next the Sun, we did endeavour with a pretty large Burning-glass to kindle it, but found, as we fear'd, That, by reason of the thickness of the Glass, (which was also of a less pure and less Diaphanous matter than the other) the Sun-beams thrown in by the Burning-glass, were in their passage so dislocated and scattered (not now to mention those many that being reflected, could not pierce into the cavity of the Receiver) that we could not possibly unite enough of them to kindle the matter, nor so much as to make it sensibly smoke. Yet we hope that the seeing whether Bodies (other than Gun-powder) may be kindled, and what would happen to them when set on fire, in a place in great measure devoid of Air, may prove so Lucilerous an Experiment, that when the Season is more favourable we shall, God permitting, make farther trial of it, and acquaint your Lordship with the Event, if it prove prosperous. In the mean time we shall pass on to other Experiments, as soon as we have advertis'd Your Lordship that we have forborn to make such Reflexions upon the several Experiments we have set down concerning Fire, as the matter would have easily afforded, and Your Lordship may perhaps have expected. But I made the less scruple to forbear the annexing of Speculations to these Recitals, because Carneades and Eleutherius have in some Dialogues concerning Heat and Flame, (which were last year seen by some Friends, and may be, when you please, commanded by You,) mention'd divers of my Thoughts and Experiments concerning Fire,

EXPERIMENT XVI.

WE designed to try whether or no divers Magnetical Experiments would exhibit any unusual Phaenomena, being made in our Evacuated Receiver instead of the open Air: But for want of leasure and conveniency to prosecute such Trials, we were induced to reserve the rest for another time, and to content our selves with making that which follows. We convey'd [Page] into the Receiver a little Pedestal of Wood, in the midst of which was perpendicularly erected a slender Iron, upon whose sharp point an excited Needle of Steel purposely made, and of about five Inches long, was so placed, that hanging in an AEquilibrium it could move freely towards either hand. Then the Air being after the usual manner pumped out, we apply'd a Load-stone moderately vigorous to the outside of the Glass, and found that it attracted or repell'd the ends of the Needle, according to the Laws Magnetical, without any remarkable difference from what the same Load-stone would have done, had none of the Air been drawn away from about the Needle, which, when the Load-stone was removed, after some tremulous Vibrations to and fro, rested in a position, wherein it look'd North and South.

EXPERIMENT XVII.

PRoceed we now to the mention of that Experiment, whereof the satisfactory trial was the principal fruit I promis'd my self from our Engine, It being then fufficiently known, that, in the Experiment De Vacuo, the Quick-silver in the Tube is wont to remain elevated, above the surface of that whereon it leans, about 27 digits: I considered, that, if the true and only reason why the Quick-silver falls no lower, be, that at that Altitude, the Mercurial Cylinder in the Tube is in an AEquilibrium with the Cylinder of Air, suppos'd to reach from the adjacent Mercury to the top of the Atmosphere: then if this Experiment could be try'd out of the Atmosphere, the Quick-silver in the Tube would fall down to a level with that in the Vessel, since then there would be no pressure upon the subjacent, to resist the weight of the Incumbent Mercury. Whence I inferr'd (as easily I might) that if the Experiment could be try'd in our Engine, the Quick-silver would subside below 27 Digits, in proportion to the exsuction of Air, that should be made out of the Receiver. For, as when the Air is shut into the Receiver, it doth (according to what hath above been taught) continue there as strongly compress'd, as it did whilst all the incumbent Cylinder of the Atmosphere [Page] lean'd immediately upon it; because the Glass, wherein it is pen'd up, hinders it to deliver it self, by an expansion of its parts, from the pressure wherewith it was shut up. So if we could perfectly draw the Air out of the Receiver, it would conduce as well to our purpose, as if we were allow'd to try the Experiment beyond the Atmosphere.

Wherefore (after having surmounted some little difficulties which occurr'd at the beginning) the Experiment was made after this manner. We took a slender and very curiously blown Cylinder of Glass, of near three foot in length, and whose bore had in Diameter a quarter of an Inch, wanting a hairs breadth: This Pipe being Hermetically seal'd at one end, was, at the other, fill'd with Quick-silver, care being taken in the filling, that as few bubbles as was possible should be left in the Mercury: Then the Tube being stopt with the Finger and inverted, was open'd, according to the manner of the Experiment, into a somewhat long and slender Cylindrical Box (instead of which we now are wont to use a Glass of the same form) half fill'd with Quick-silver: And so, the liquid metal being suffered to subside, and a piece of Paper being pasted on level with its upper surface, the Box and Tube and all were by strings carefully let down into the Receiver: And then, by means of the hole formerly mentioned to be left in the Cover, the said Cover was slipt along as much of the Tube as reached above the top of the Receiver; And the Interval, left betwixt the sides of the Hole and those of the Tube, was very exquisitely filled up with melted (but not over hot) Diachylon, and the round chink, betwixt the Cover and the Receiver, was likewise very carefully closed up: Upon which closure there appeared not any change in the height of the Mercurial Cylinder; no more, than if the interposed Glass Receiver did not hinder the immediate pressure of the ambient Atmosphere upon the inclosed Air; which hereby appears to bear upon the Mercury, rather by virtue of its spring than of its weight: since its weight cannot be supposed to amount to above two or three Ounces, which is inconsiderable in comparison of such a Cylinder of Mercury as it would keep from subsiding.

[Page]All things: being thus in a readiness, the Sucker was drawn down; and, immediately upon the egress of a Cylinder of Air out of the Receiver, the Quick silver in the Tube did, according to expectation, subside: And notice being carefully taken (by a mark fastened to the outside) of the place where it stopt, we caused him that managed the Pump to pump again, and marked how low the Quick-silver fell at the second exsuction; but continuing this work, we were quickly hindred from accurately marking the Stages made by the Mercury in its descent, because it soon sunk below the top of the Receiver, so that we could henceforward mark it no other ways than by the eye. And thus, continuing the labour of pumping for about a quarter of an hour, we found our selves unable to bring the Quick-silver in the Tube totally to subside; because, when the Receiver was considerably emptyed of its Air, and consequently that little that remained grown unable to resist the Irruption of the External, that Air would (in spight of whatever we could doe) press in at some little Avenue or other; and though much could not thereat get in, yet a little was sufficient to counterballance the pressure of so small a Cylinder of Quick-silver, as then remained in the Tube.

Now (to satisfy our selves farther, that the falling of the Quick-silver in the Tube to a determinate height, proceedeth from the AEquilibrium, wherein it is at that height with the external Air, the one gravitating, the other pressing with equal force upon the subjacent Mercury) we returned the Key and let in some new Air; upon which the Mercury immediately began to ascend (or rather to be impelled upwards) in the Tube, and continued ascending, till having returned the Key, it immediately rested at the height which it had then attained: And so, by turning and returning the Key, we did several times at pleasure impell it upwards, and check its ascent. And lastly, having given a free egress at the Stop-cock to as much of the external Air as would come in, the Quick-silver was impelled up almost to its first height: I say almost, because it ftopt near a quarter of an Inch beneath the Paper mark formerly mentioned; which we ascri [...]ed to this, That there was (as is usual in this Experiment) some little Particles of Air engaged among those [Page] of the Quick-silver; which Particles, upon the descent of the Quick-silver, did manisestly rise up in bubbles towards the top of the Tube, and by their pressure, as well as by lessening the Cylinder by as much room as they formerly took up in it, hindred the Quick-silver from regaining its first height.

This Experiment was a few days after repeated in the presence of those excellent and deservedly Famous Mathematick Professors, Dr. Wallis, Dr. Ward, and Mr. Wren, who were pleased to honour it with their Presence: And whom I name, both as justly counting it an Honour to be known to them, and as being glad of such Judicious and illustrious Witnesses of our Experiment; and'twas by their guess, that the top of the Quick-silver in the Tube was defined to be brought within an Inch of the surface of that in the Vessel.

And here, for the Illustration of the foregoing Experiment, it will not be amiss to mention some other particulars relating to it.

First then, When we endeavoured to make the Experiment with the Tube closed at one end with Diachylon instead of an Hermetical Seal; we perceived, that upon the drawing of some of the Air out of the Receiver, the Mercury did indeed begin to fall, but continued asterwards to subside, though we did not continue pumping. When it appeared, that though the Diachylon that stopt the end of the Tube, were so thick and strong, that the external Air could not press it in (as experience taught us that it would have done, if there had been but little of it) yet the subtler parts of it were able (though slowly) to insinuate themselves through the very body of the Plaister, which it seems was not of so close a Texture, as that which we mentioned our selves to have successfully made use of in the Experiment De Vacuo some years ago. So that now we begin to suspect, that perhaps one reason, why we cannot persectly pump out the Air, may be, that when the Vessel is almost empty, some of the subtler parts of the external Air may, by the pressure of the Atmosphere, be strained through the very body of the Diachylon into the Receiver. But this is only conjecture.

[Page]Another Circumstance of our Experiment was this, That, if (when the Quick-silver in the Tube was fallen low) too much ingress were, at the hole of the Stop-cock, suddenly permitted to the external Air; it would rush in with that violence, and bear so forcibly upon the surface of the subjacent Quick-silver, that it would impell it up into the Tube rudely enough to endanger the breaking of the Glass.

We formerly mention'd, that the Quick-silver did not in its descent fall as much at a time after the two or three first exsuctions of the Air, as at the beginning. For, having marked its several Stages upon the Tube, we found, that at the first suck it descended an Inch and ⅜, and at the second an Inch and ⅜; and when the Vessel was almost emptied, it would scarce at one exsuction be drawn down above the breadth of a Barly-corn. And indeed we found it very difficult to measure in what proportion these decrements of the Mercurial Cylinder did proceed: Partly because (as we have already intimated) the Quick-silver wassoon drawn below the top of the Receiver; and partly because, upon its descent at each exsuction, it would immediately re-ascend a little upwards; either by reason of the leaking of the Vessel at some imperceptible hole or other, or by reason of the motion of restitution in the Air, which, being somewhat compresled by the fall as well as weight of the Quick-silver, would repell it a little upwards, and make it vibrate a little up and down, before they could reduce each other to such an AEquilibrium as both might rest in. But though we could not hitherto make observations accurate enough concerning the measures of the Quick-silver's descent, to reduce them into any Hypothesis, yet would we not discourage any from attempting it; since, if it could be reduc'd to a certainty, 'tis probable that the discovery would not be unusefull.

And, to illustrate this matter a little more, we will add, That we made a shift to try the Experiment in one of our above-mention'd small Receivers, not containing a Quart; but (agreeably to what we formerly observed) we found it as difficult to bring this to be quite empty as to evacuate the greater; the least external [Page] Air that could get in (and we could not possibly keep it all perfectly out) sufficing in so small a Vessel to display a considerable pressure upon the surface of the Mercury, and thereby hinder that in the Tube from falling to a level with it. But this is remarkable, that having two or three times try'd the Experiment in a small Vessel, upon the very first Cylinder of Air that was drawn out of the Receiver, the Mercury fell in the Tube 18 Inches and a half, and at another trial 19 Inches and a half.

But on this occasion, I hold it not unfit to give your Lordship notice that I hop'd from the descent of the Quick-silver in the Tube upon the first suck, to derive this advantage: that I should thence be enabled to give a near guess at the proportion of force betwixt the pressure of the Air (according to its various states, as to Density and Rarefraction) and the gravity of Quick-silver, than hitherto hath been done. For in our Experiment there are divers things given, that may be made use of towards such a discovery. For first we may know the capacity of the Receiver wherein the Experiment is made, since, by filling it with water, we may easily compute how many Quarts, or Measures of any other denomination, it containeth of Air; which Air, when shut up in the Vessel may be suppos'd to have a pressure equal to that of the Atmosphere; since it is able to keep the Quick-silver in the Tube from falling any lower than it did in the free and open Air. Next here is given us the capacity of the brass Cylinder empty'd by the drawing down of the Sucker (its bore and height being mention'd in the description of our Pump) whereby we may come to know how much of the Air contain'd in the Receiver is drawn out at the first-suck. And we may also easily define, either in weight or cubick measures, the Cylinder of Quick silver that answers to the Cylinder of Air lately mention'd (that Mercurial Cylinder being in our Engine computable by deducting from the entire altitude of that Cylinder of Quick-silver, the altitude at which it rests upon the first exsuction.) But though, if this Experiment were very watchfully try'd in Vessels of several sizes, and the various descents of the Quick-silver [Page] compar'd among themselves, 'tis not improbable, that some such things, as we hop'd for, may thereby be discovered. Yet because not only the solid contents of as much of the Glass-tube as remains within the concave surface of the Receiver, and (which is more difficult) the varying contents of the Vessel containing the Mercury, and of as much of the Mercury it self as is not in the Tube, must be deducted out of the capacity of the Receiver, but there must also an allowance be made for this, that the Cylinder that is empty'd by the drawing down of the Sucker, and comes to be fill'd upon the letting of the Air out of the Receiver into it, is not so replenish'd with Air as the Receiver it self at first was: because there passeth no more Air out of the Receiver into the Cylinder, than is requisite to reduce the Air in the cavity of the Cylinder, and in that of the Receiver to the same measure of dilatation. Because of these (I say) and some other difficulties that require more skill in Mathematicks than I pretend to, and much more leasure than my present occasions would allow me, I was willing to refer the nicer consideration of this matter to some of our Learned and accurate Mathematicians, thinking it enough for me to have given the Hint already suggested.

For farther confirmation of what hath been delivered, we likewise tried the Experiment in a Tube of less than two foot long: and, when there was so much Air drawn out of the Vessel, that the remaining Air was not able to counterballance the Mercurial Cylinder, the Quick-silver in the Tube subsided so visibly, that (the Experiment being try'd in the little Vessel lately mention'd) at the first suck it fell above a span, and was afterwards drawn lower and lower for a little while; and the external Air being let in upon it, impell'd it up again almost to the top of the Tube: So little matters it how heavy or light the Cylinder of Quicksilver to subside is, provided its gravity overpower the pressure of as much external Air as bears upon the surface of that Mercury into which it is to fall.

Lastly we also observ'd, That if (when the Mercury in the Tube had been drawn down, and by an Ingress permitted to the [Page] external Air, impell'd up again to its former height) there were some more Air thrust up by the help of the Pump into the Receiver, the Quick-silver in the Tube would ascend much above the wonted height of 27 digits, and immediately upon the letting out of that Air would fall again to the height it rested at before.

Your Lordship will here perhaps expect, that as those who have treated of the Torricellian Experiment, have for the most part maintained the Affirmative, or the Negative of that famous Question, Whether or no that Noble Experiment infer a Vacuum? so I should on this occasion interpose my Opinion touching that Controversie, or at least declare whether or no, in our Engine, the exsuction of the Air do prove the place deserted by the Air suck'd out, to be truly empty, that is, devoid of all Corporeal Substance. But besides, that I have neither the leasure, nor the ability, to enter into a solemn Debate of so nice a Question; Your Lordship may, if you think it worth the trouble, in the Dialogues not long since referr'd to, find the Difficulties on both sides represented; which then made me yield but a very wavering assent to either of the parties contending about the Question: Nor dare I yet take upon me to determine so difficult a Controversie.

For on the one side it appears, that notwithstanding the exsuction of the Air, our Receiver may not be destitute of all Bodies, since any thing placed in it, may be seen there; which would not be, if it were not pervious to those beams of Light which rebounding from the seen Object to our eyes, affect us with the sense of it: And that either these Beams are Corporeal Emanations from some lucid body, or else at least, the light they convey doth result from the brisk motion of some subtle Matter, I could, if I mistake not, sufficiently manifest out of the Dialogues above-mention'd, if I thought Your Lordship could seriously imagine that Light could be convey'd without, at least, having, (if I may so speak) a Body for its Vehicle.

By the sixteenth Experiment, it also appears that the closeness of our Receiver hinders it not from admitting the Effluvia [Page] of the Load-stone; which makes it very probable that it also freely admits the Magnetical steams of the Earth; concerning which, we have in another Treatise endeavour'd to manifest that numbers of them do always permeate our Air.

But on the other side it may be said, That as for the subtle Matter which makes the-Objects enclosed in our evacuated Receiver, visible, and the Magnetical Effluvia of the Earth that may be presum'd to pass thorow it, though we should grant our Vessel not to be quite devoid of them, yet we cannot so reasonably affirm it to be replenish'd with them, as we may suppose, that if they were gather'd together into one place without Intervals between them, they would fill but a small part of the whole Receiver. As in the thirteenth Experiment, a piece of Match was inconsiderable for its bulk, whilst its parts lay close together, that afterwards (when the Fire had scatter'd them into smoke) seem'd to replenish all the Vessel. For (as elsewhere our Experiments have demonstrated) both Light and the Effluvia of the Load-stone, may be readily admitted into a Glass, Hermatically seal'd, though before their Admission, as full of Air as hollow Bodies here below are wont to be; so that upon the exsuction of the Air, the large space deserted by it, may remain empty, notwithstanding the pretence of those subtle Corpuscles, by which Lucid and Magnetical Bodies produce their effects.

And as for the Allegations above mention'd, they seem'd to prove but that the Receiver devoid of Air, may be replenish'd with some Etherial matter, as some Modern Naturalists write of but not that it really is so. And indeed to me it yet seems, that as to those spaces which the Vacuists would have to be empty, because they are manifestly devoid of Air; and all grosser Bodies the Plenists (if I may so call them) do not prove that such spaces are replenish'd with such a subtle matter as they speak of, by any sensible effects, or operations of it (of which divers new Trials purposely made, have not yet shewn me any) but only conclude that there must be such a Body, because there cannot be a Void. And the reason why there cannot be a Void, [Page] being by them taken, not from any Experiments, or Phaenomena of Nature, that clearly and particularly prove their Hypothesis, but from their notion of a Body, whose Nature, according to them, consisting only in extension (which indeed seems the property most essential to, because inseparable from a Body) to say a space devoid of Body, is to speak in the Schoolmens Phrase, a Contradiction in Adjecto. This reason I say, being thus desum'd, seems to make the Controversie about a Vacuum, rather a Metaphysical, than a Physiological Question; which therefore we shall here no longer debate, finding it very difficult either to satisfie Naturalists with this Cartesian Notion of a Body, or to manifest wherein it is erroneous, and substitute a better in its stead.

But though we are unwilling to examine any farther the Inferences wont to be made from the Torricellian Experiment, yet we think it not impertinent to present Your Lordship with a couple of Advertisements concerning it.

First, then if in trying the Experiment here or elsewhere, you make use of the English measures that Mathematicians and Tradesmen are here wont to employ, You will, unless you be forewarn'd of it, be apt to suspect that those that have written of the Experiment have been mistaken. For whereas men are wont generally to talk of the Quick-silver's remaining suspended at the height of between six or seven and twenty Inches; we commonly observed, when divers years since we first were solicitous about this Experiment, that the Quick-silver in the Tube rested at about 29 Inches and a half above the surface of the Restagnant Quick-silver in the Vessel, which did at first both amaze and perplex us, because though we held it not improbable that the difference of the grosser English Air, and that of Italy and France, might keep the Quick-silver from falling quite as low in this colder, as in those warmer Climates; yet we could not believe that that difference in the Air should alone be able to make so great an one in the heights of the Mercurial Cylinders; and accordingly upon enquiry we found, that though the various density of the Air be not to be over-looked in this Experiment, [Page] yet the main Reason why we found the Cylinder of Mercury to consist of so many Inches, was this, That our English Inches are somewhat inferiour in length to the digits made use of in Foreign Parts, by the Writers of the Experiment.

The next thing I desire Your Lordship to take notice of, is, That the height of the Mercurial Cylinder is not wont to be found altogether so great as really it might prove, by reason of the negligence or incogitancy of most that make the Experiment. For oftentimes upon the opening of the inverted Tube into the Vessel'd Mercury, you may observe a bubble of Air to ascend from the bottom of the Tube through the subsiding Quick-silver to the top; and almost always you may, if you look narrowly, take notice of a multitude of small bubbles all along the inside of the Tube betwixt the Quick-silver and the Glass: (not now to mention the Particles of Air that lie concealed in the very Body of the Mercury) Many of which, upon the Quicksilver's forsaking the upper part of the Tube, do break into that deserted space where they find little or no resistance to their expanding of themselves. Whether this be the reason that upon the Application of warm Bodies to the emptied part of the Tube, the subjacent Mercury would be depressed somewhat lower, we shall not determine; though it seem very probable, especially since we found, that, upon the application of Linnen cloaths dipped in Water, to the same part of the Tube, the Quick-silver would somewhat ascend; as if the cold had condensed the imprisoned Air, (that pressed upon it,) into a lesser room. But that the deserted space is not wont to be totally devoid of Air, we were induced to think by several Circumstances. For when an eminent Mathematician, and excellent Experimenter, had taken great pains and spent much time in accurately filling up a Tube of Mercury, we found that yet there remained store of inconspicuous bubbles, by inverting the Tube, letting the Quick-silver fall to its wonted height; and by applying (by degrees) a red hot Iron to the outside of the Tube, over against the upper part of the Mercurial Cylinder, (for hereby the little unheeded bubbles, being mightily expanded, ascended [Page] in such numbers, and so fast to the deserted space, that the upper part of the Quick-silver seemed, to our wonder, to boil.) We farther observed, That in the trials of the Torricellian Experiment we have seen made by others, and (one excepted) all our own, we never found that upon the inclining of the Tube the Quick-silver would fully reach to the very top of the sealed end: Which argued, that there was some Air retreated thither that kept the Mercury out of the unreplenished space.

If Your Lordship should now demand what are the best expedients to hinder the intrusion of the Air in this Experiment; we must answer, That of those which are easily intelligible without ocular demonstration, we can at present suggest, upon our own trials, no better than these. First, at the open end of the Tube the Glass must not only be made as even at the edges as you can, but it is very convenient (especially if the Tube be large) that the bottom be every way bent inwards, that so the Orifice, not much exceeding a quarter of an Inch in Diameter, may be the more easily and exactly stopped by the Experimenter's finger; between which and the Quick-silver, that there may be no Air intercepted (as very often it happens that there is) it is requisite that the Tube be filled as full as possibly it can be, that the finger which is to stop it, pressing upon the accumulated and protuberant Mercury, may rather throw down some, than not find enough exactly to keep out the Air. It is also an usefull and compendious way not to fill the Tube at first quite of Mercury, but to leave near the top about a quarter of an Inch empty; for if you then stop the open end with your finger, and invert the Tube, that quarter of an Inch of Air will ascend in a great bubble to the top, and in its passage thither, will gather up all the little bubbles, and unite them with it self into one great one; so that if by reinverting the Tube, you let that bubble return to the open end of it, you will have a much closer Mercurial Cylinder than before, and need but to add a very little Quick-silver more to fill up the Tube exactly. And lastly, as for those lesser and inconspicuous parcels of Air which cannot this [Page] way begleaned up, You may endeavour before you invert the Tube, to free the Quick-silver from them by shaking the Tube, and gently knocking on the outside of it, after every little parcel of Quick-silver which you pour in; and afterwards, by forcing the small latitant bubbles of Air to disclose themselves and break, by imploying a hot Iron in such manner as we lately mentioned. I remember that by carefully filling the Tube, though yet it were not quite free from Air, we have made the Mercurial Cylinder reach to 30 Inches and above an eight, and this in a very short Tube: which we therefore mention, because we have found, by Experience, that in short Tubes a little Air is more prejudicial to the Experiment than in long ones, where the Air having more room to expand it self, doth less potently press upon the subjacent Mercury.

And since we are fallen upon the consideration of the Altitude of the Mercurial Cylinder, I must not conceal from Your Lordship an Experiment relating thereunto, which perhaps will set both You and many of your Friends the Vertuosi on thinking; and, by disclosing some things about the Air or Atmosphere, that have scarce hitherto been taken notice of, may afford you some hints conducive to a further discovery of the subject of this Epistle.

EXPERIMENT XVIII.

WE took a Glass Tube, which though it were not much above three Foot long, we made choice of, because it was of a more than ordinarily even thickness. This we fill'd with Mercury, though not with as much care as we could, yet with somewhat more than is wont to be used in making the Torricellian Experiment. Then, having according to the manner inverted the Tube, and open'd the mouth of it beneath the surface of some other Quick-silver, that in the Tube fell down to the wonted height, leaving, as is usual, some little Particles of Air in the space it deserted, as we guest by observing, that upon the Application of hot Bodies to the upper part of the Tube, the Quicksilver would be a little depress'd. Lastly, having put both the [Page] Tube and the Vessel it lean'd on into a convenient Wooden frame to keep them from mischances: we plac'd that Frame in a Window within my Bed-chamber, that I might both keep the Mercury from being stirr'd, and have opportunity to watch from time to time the Phaenomena it was to exhibit. For the better discovery of which, when the Quick-silver both in the Tube and subjacent Vessel was perfectly at rest, we took notice, by a mark made on the outside of the Glass, how high the included Liquor then reach'd.

During several Weeks that the Tube was kept in that Windown (which was very rarely open'd) I had the opportunity to observe, that the Quick-silver did sometimes faintly imitate the Liquor of a Weather-glass, subsiding a little in warm, and rising a little in cold Weather, which we ascribed to the greater or lesser pressure of that little Air that remain'd at the top of the Tube, expanded or condens'd by the heat or cold that affected the ambient Air. But that which I was chiefly carefull to observe, was this, That oftentimes the Quick-silver did rise and fall in the Tube, and that very notably, without conforming it self to what is usual in Weather-glasses, whose Air is at the top, nay quite contrary thereunto: for sometimes I observ'd it in very cold weather (such as this Winter hath already afforded us good store of) to fall down much lower than at other times, when by reason of the absence of both Frost, Snow, and sharp Winds, the Air was comparatively much warmer. And I farther observ'd, That sometimes the Quick-silver would for some days together rest almost at the same height; and at other times again it would in the compass of the same day considerably vary its altitude, though there appear'd no change either in the Air abroad, or in the temper of the Air within the Room (wherein was constantly kept a good Fire) nor in any thing else, to which either I, or some eminently Learned Men, whom I then acquainted with the Experiment, could reasonably impute such a change: Especially considering that the space wherein the Mercury wandred up and down, within about five Weeks, amounted to full two Inches, of which we found by our several marks whereby [Page] we had taken notice of its several removes, that it had descended about 9/16 of an Inch from the place where it first setled, and the other Inch and 7/16 it had ascended. And it seems probable that the height of the Mercurial Cylinder would have varied yet more, if the Experiment had been made in the open Air, and in a long Tube, where the Particles of the imprison'd Air by having more room to display themselves in, might not have had so strong a Spring to work upon the Quick-silver with. But for want both of time and of a competent quantity of Mercury (which was not to be procur'd where we then happen'd to be) we were unable to make any farther tryals: which therefore chiefly troubled us, because we would gladly have try'd an ingenious Experiment which was suggested unto us by that excellent Mathematician Mr. Wren, who being invited to name any thing he would have us try touching the pressure of the Air, desired us to observe whether or no the Quick-silver in a long Tube would not a little vary its height according to the Tides, especially about the New and Full Moon; about which times Mariners observe those great Flowings and Ebbs of the Sea, that they call the Spring-Tides. For he sagaciously and plausibly conjectur'd that such observations, accurately made, would discover the truth or erroneousness of the Cartesian Hypothesis concerning the Ebbing and Flowing of the Sea: which Des Cartes ascribeth to the greater pressure made upon the Air by the Moon, and the Intercurrent Ethereal Substance at certain times (of the Day, and of the Lunary Month) than at others. But in regard we found the Quick-silver in the Tube to move up and down so uncertainly, by reason, as it seems, of accidental mutation in the Air; I somewhat doubt: whether we shall find the Altitude of the Quick-silver to vary as regularly as the Experiment is ingeniously propos'd. The success we shall (God permitting us to make tryal of it) acquaint your Lordship with; and in the mean time take notice, that when we had occasion to take the Tube out of the Frame (after it had staid there part of November and part of December) a good Fire being then in the room, because it was a Snowy day, we found the Quick-silver in the Tube to be above the upper [Page] surface of the subjacent Mercury 29 Inches three quarters.

If Your Lordship should now aske me what are the true causes of this varying altitude of the Mercurial Cylinder; I should not undertake to answer so difficult a question, and should venture to say no more, than that among divers possible causes to which it may be ascribed, it would not be, perhaps, absurd to reckon these that follow.

First then we may consider, that the Air in the upper part of the Tube is much more rarefied, and therefore more weak than the External Air, as may appear by this among other things, That upon the inclining of the Tube, the Quick-silver will readily ascend almost to the very top of it, and so take up eight or nine tenth parts, and perhaps more of that space which it deserted before: which would not happen, if that whole space had been full of unrarefied Air, since that (as tryal may easily satisfie you) would not have suffer'd it self to be thrust into so narrow a room by so weak a pressure. So that although in our Tube when the included Air, was heated, the Quick-silver was somewhat depress'd; yet there is this difference betwixt such a Tube and common Weather-Glasses, that in these the included and the ambient Air are in an AEquilibrium as to pressure, and the weight of the Water that keeps them separate is scarce considerable. Whereas in such a Tube as we are speaking of, the Air within, is very much more dilated than that without. And 'tis not so much the spring or resistance of the included Air, as the weight of the Mercurial Cylinder it self, that hinders the Quick-silver from ascending higher: For if we should suppose that deserted part of the Tube perfectly devoid of Air, yet would the Quick-silver rise but a little higher in it, and be far from filling it; in regard the outward Air would not be able to impell up such a weight much higher: whereas it may, by our former Experiments appear, that if all the Air in the upper part of the Weather-Glass were away, the Water would be impell'd up to the very top of it, though the Pipe were above thirty foot long.

We may next consider, that this rarefied: Air at the upper part of our Tube being exactly shut up betwixt the Glass and [Page] the Quick-silver, it was scarce subject to any discernable alterations, save those it receiv'd from heat and cold.

And we may farther consider, that yet the external Air or Atmosphere is subject to many alterations, besides them that proceed from either of those Qualities.

For the Experiment that occasion'd this Discourse, seems to make it probable enough, that there may be strange Ebbings and Flowings, as it were, in the Atmosphere, or at least, that it may admit great and sudden Mutations, either as to its Altitude or its Density, from causes, as well unknown to us, as the effects are unheeded by us. And that You may not think that there is nothing in Nature but our Experiment that agrees with this our conjecture, we might put Your Lordship in mind of the Pains and Aches that are often complain'd of by those that have had great Wounds or Bruises, and that do presage great Mutations in the Air oftentimes, whilst to strong and healthy Persons no sign of any such thing appears. And that is also very memorable to this purpose, which I remember I have somewhere read in a Book of the Ingenious Kircherus, who giving a pertinent admonition concerning the various refractions that may happen in the Air, relateth, That during his stay in Malta, he often saw Mount AEtna, though the next day, notwithstanding its being extremely clear, he could not see it; adding, that Vintemillius, a very Learned Person, did oftentimes, from a Hill he names, behold the whole Island he calls Luprica protuberant above the Sea, though at other times, notwithstanding a clear Sky, he could not see it. And though perhaps this may be in part ascribed to the various light and position of the Sun, or to the various disposition of the Spectators eye, or peradventure to some other cause; yet the most probable cause seems to be the differing Density of the Air, occasion'd by Exhalations capable to increase the refraction, and consequently bring Beams to the Eye, which otherwise would not fall on it. We have likewise, in another Treatise, mention'd our having often observ'd with Telescopes a plenty of Steams in the Air, which without such a help would not be taken notice of, and which, as they were [Page] not at all times to be seen even through a Telescope, so they did sometimes, especially after a shower of Rain, hastily disappear: and when we have visited those places that abound with Mines, we have several times been told by the Diggers, that even when the Sky seem'd clear, there would, not seldome, suddenly arise, and sometimes long continue, a certain Steam (which they usually call a damp) so gross and thick that it would oftentimes put out their very Candels, if they did not seasonably prevent it. And I think it will easily be granted, that the ascension of such Steams into this or that part of the Air, and their mixing with it, are very like to thicken it; as on the other side either heat or the sudden condensation of the Air in another part of the Atmosphere (to mention now no other causes) are capable of rarefying it.

Nor will it very much import the main scope of our Discourse, whether it be suppos'd that the copious Steams the earth sends into the Air, thicken that part of the Atmosphere that receives them, and make it more heavy: Or that sometimes the Fumes may ascend with such celerity, that though the Air be thickn'd yet they rather diminish than encrease its gravitation, in regard that the quickness of their ascent, not onely keeps them from gravitating themselves, but may hinder the pressing downwards of many Aërial Corpuscles that they meet with in their way upwards. This I say, is of no great importance to our present Discourse, since either way the Terrestrial Steam may here and there considerably alter the gravity or pressure of the Atmosphere.

Your Lordship may also be pleased to remember, That by our seventeenth Experiment it appear'd, that, as when the Air in the Receiver was expanded more than ordinarily, the Quick-silver in the Tube did proportionably subside; so when the Air in the same Receiver was a little more than ordinarily compress'd, it did impell up the Quick-silver in the Tube, above the wonted height of betwixt six and seven and twenty digits.

And if to these things we annex, that for ought we can find by tryals purposely made, the degree of rarity or density of the Air, shut up into our Receiver, doth not sensibly alter its temperature [Page] as to cold or heat. It will not, I hope, appear absurd to conceive, That since the Air, included in the Tube, could but very saintly hinder the ascent of the Quick-silver, or press it downwards; Since too, that included Air could scarce immediately receive any sensible alteration, save either by heat or cold; And since also, that according to the bare density or rarity of the Air incumbent on the subjacent Quick-silver in the Vessel, that in the Tube was impell'd more or less high; such changes happening in the neighbouring part of the outward Air, either by the ascension of gross or copious exhalations, or by any other cause (of which there may be divers) as were capable to make considerable alterations in the consistence of the Air, as to rarity and density, may be able proportionably to alter the height of the Quick-silver. I rather say, that such alterations may be, than that they are the causes of our Phaenomenon: because I think it sufficient, if I have propos'd conjectures not altogether irrational about a new Mystery of Nature, touching which, the chief things I pretend to, is to give occasion to the Curious to enquire farther into it, than I have been yet able to do.

EXPERIMENT XIX.

THe same Reason that mov'd us to conclude, that by the drawing of the Air out of the Receiver, the Mercury would descend in a Tube shorter than six and twenty digits, induc'd us also to expect, that by the same means Water might be brought to subside in Glass Tubes of a moderate length: Though by the noble Experiment, said to have been accurately made in France, by Monsieur Paschal, we are informed that a Tube of no less than about two and thirty Foot; was found requisite to make the Experiment De vacuo succeed with Water instead of Quick-silver: so tall a Cylinder of that lighter Liquor, being it seems, requisite to equal the Weight of a Mercurial Cylinder of six or seven and twenty digits, and surmount the pressure of the Atmosphere.

We took then a Tube of Glass, Hermetically seal'd at one end, of about four foot in length, and not very slender: This, [Page] at the open end, we fill'd with common Water, and then stopt that end till we had inverted the Tube, and open'd it beneath the surface of a quantity of the like Water, contain'd in a somewhat deep and slender Vessel. This Vessel, with the Tube in it, was let down into the Receiver, and the Receiver being clos'd up after the accustom'd manner, the Pump was set on work.

As much of the event as concerns our present purpose, was this, That till a considerable part of the Air was drawn out of the Receiver, the Tube continu'd top-full of Water as when it was put in, it being requisite that a great part of the Air, formerly contain'd in the Receiver, should be drawn out, to bring the remaining Air to an AEquilibrium, with so short and light a Cylinder of Water. But when once the Water began to fall in the Tube, then each exsuction of Air made it descend a little lower, though nothing near so much as the Quick-silver at the beginning did in the Experiment formerly mention'd. Nor did there appear so much inequality in the spaces transmitted by the Water in its descent, as there it did in those observ'd in the fall of the Quick-silver, of which the cause will scarce seem abstruse to him that shall duly reflect upon what hath been already deliver'd. And whereas we drew down the Quick-silver in the Tube so far as to bring it within an Inch of the surface of the other Quick-silver into which it was to fall; the lowest we were able to draw down the Water was, by our conjecture, to about a Foot or more above the surface of that in the Vessel; of which I know not whether it will be needfull to assign so obvious a cause as that, though the little Air remaining in the Receiver could not hinder a Cylinder of above on Inch high of Quick-silver from subsiding; yet it might be very well able, by its pressure, to countervail the weight of a Cylinder of a Foot long or more, of a Liquor so much less ponderous than Quick-silver, as Water is. And in fine, to conclude our Experiment, when the Water was drawn down thus low, we found, that by letting in the outward Air, it might be immediately impell'd up again to the higher parts of the Tube.

We will adde no more concerning this Experiment, save that [Page] having try'd it in one of our small Receivers, we observ'd, That upon the first exsuction of the Air the Water did usually subside divers Inches, and at the second (exsuction) fall down much lower, subsiding sometimes near two Foot; as also that upon the letting in of the Air from without, the Water was impell'd up with very great celerity.

EXPERIMENT XX.

THat the Air hath a notable Elastical power (whencesoever that proceeds) we have, I suppose, abundantly evinc'd, and it Begins to be acknowledg'd by the eminentest Modern Naturalists. But whether or no there be in Water so much as a languid one, seems hitherto to have been scarce consider'd nor hath been yet, for ought I know, determin'd either way by any Writer, which invited us to make the following Experiment.

There was taken a great Glass bubble, with a long neck; (such as Chymists are wont to call a Philosophical Egge) which being fill'd with common Water till the Liquor reach'd about a span above the bubble, and a piece of Paper being there pasted on, was put unstop'd into the Receiver, and then the Air was suck'd out after the wonted manner. The event was this, that a considerable part of the Air, pen'd up in the Receiver, was drawn out, before we discern'd any expansion of the Water; but, continuing the labour of pumping, the Water manifestly began to ascend in the stem of the Glass, and divers bubbles loosening themselves from the lower parts of the Vessel, made their way through the Body of the Water, to the top of it, and there brake into the Receiver: And after the Water once appear'd to swell, then at each time the Stop cock was turn'd to let out the Air from the Receiver into the Pump, the Water in the Neck of the Glass did suddenly rise about the breadth of a Barly-corn in the Neck of the Glass and so attain'd by degrees, to a considerable height above the mark formerly mention'd. And at length (to make the expansion of the Water more evident) the outward Air was suddenly let in, and the Water immediately subsided and deserted all the space it had newly gain'd in the Glass.

[Page]And, on this occasion, it will not perhaps be amiss to acquaint Your Lordship here (though we have already mention'd it in another Paper, to another purpose) with another Expedient that we made use of two or three years ago, to try whether or no Water had a Spring in it. About that time then, That Great and Learned Promoter of Experimental Philosophy Dr. Wilkins, doing me the Honour to come himself, and bring some of his inquisitive Friends to my Lodging, we there had in readiness a round and hollow Vessel of Pewter, great enough to contain two pounds of Water, and exactly close every where, but at one little hole where it was to be fill'd, then partly by sucking out the Air, and partly by injecting Water with a Syringe, it was (not without some difficulty) fill'd up to the top; and that hole being plac'd directly upwards, there was a little more Water leisurely forc'd in by the Syringe. Upon which, though the Vessel were permitted to rest, and the hole kept in its former posture, yet the compress'd Water leisurely swell'd above the Orifice of the hole, and divers drops ran over along the sides of the Vessel. After this we caus'd a skilfull Pewterer (who had made the Globe) to close it up in our presence with Soder so exquisitely, that none suspected there was any thing left in it besides Water. And lastly, the Vessel thus soder'd up, was warily and often struck in divers places with a Wooden Mallet, and thereby was manifestly compress'd, whereby the inclosed Water was crouded into less room than it had before: And thereupon we took a Needle, and with it and the Mallet perforated the Vessel, and drew out the Needle again; the Water (but in a very slender Stream) was suddenly thrown after it into the Air, to the height of two or three Feet. As for the other Phaenomena of this Experiment, since they belong not to our present purpose, and are partly mention'd in another of our Papers, we shall, instead of recording them here, give this Advertisement: That as evidently as this Experiment, and that made in our Receiver, seem to prove a power in the Water to expand and restore it self after compression; yet for a reason to be met with ere long, I judged it not safe, to infer that Conclusion from these Premises, till I had made some [Page] of the following tryals, to the mention of which I will therefore hasten.

EXPERIMENT XXI.

TO discover whether the Expansion of the Water really proceeded from an Elastical power in the parts of the Water it self, we thought it requisite to try two things: The one, Whether or no the Atmosphere gravitates upon Bodies under Water; and the other, Whether in case it do gravitate, the Intumescence of the Water may not be ascribed to some substance subtler than it self, residing in it. In order to the satisfying myself about the first of these, I intended to let down into the Receiver a Vessel of Water, wherein should be immers'd a very small oyl'd Bladder, almost devoid of Air, but strongly ty'd up at the Neck with a string, and detain'd a little under Water by such a weight fasten'd to that string, as should just be able to keep the Bladder from swimming, and no more. For I suppos'd, that if when all things were thus order'd, the Receiver were empty'd, in case there were any such pressure of the Atmosphere upon Water, as I was inclin'd to believe, the Air within the Bladder, being upon the exsuction of the Air within the Receiver, freed from that pressure, and being press'd onely by the small weight of the incumbent Water, would considerably expand it self; but whilst we were preparing Bladders for this Experiment, there occurr'd an easie way for the making at once both the Discoveries I desir'd.

We took then a Glass Viol, containing by ghess a pound and some ounces of Water, this we fill'd top full, and then we put into the Neck of it a Glass Pipe a pretty deal bigger than a Goose Quill, open at both ends, and of divers Inches in length: One end of this Pipe was so put into the Neck of the Viol, as to reach a little below it, and then was carefully cemented thereto that no Air might get into the Viol, nor any Water get out of it, otherwise than through the Pipe; and then the Pipe being warily fill'd, about half way up to the top, with more Water, and a mark being pasted over aganst the upper surface of the Liquor; the Viol thus fitted with the Pipe, was, by strings let [Page] down into the Receiver, and according to the wonted manner exquisitely clos'd up in it.

This done, we began to pump out the Air, and when a pretty quantity of it had been drawn away, the Water in the Pipe began to rise higher in the Pipe, at the sides of which some little bubbles discover'd themselves. After a little while longer, the Water still swelling, there appear'd at the bottom of the Pipe a bubble about the bigness of a small Pea, which ascending through the Pipe to the top of the Water, stay'd there a while and then broke; but the Pump being nimbly ply'd, the expansion of the Water so encreas'd, that quickly, getting up to the top of the Pipe, some drops of it began to run down along the out-side of it, which oblig'd us to forbear pumping a while, and give the Water leave to subside within less than two Inches of the bottom of the Pipe. After this the Pump being again set on work, the bubbles began to ascend from the bottom of the Pipe, being not all of a size, but yet so big, that estimating one with another, they appear'd to be of the size of the smaller sort of Peas; and of these we reckon'd about sixty which came up one after another, besides store of smaller ones, of which we made no reckoning: And at length, growing weary of reckoning and pumping too (because we found, that in spight of all our pains and industry, some undiscern'd Leak or other in the Receiver hinder'd us from being able to empty it altogether) we thought fit to desist for that time, after tryal made of what operation the external Air, being let in upon the expanded Water, would have; and accordingly turning the Key to let in the Air, we saw, as we expected, that the Water in the Pipe in a moment fell down almost to the bottom of it.

Now of this Experiment there are two or three Circumstances yet to be mention'd, which are no less, than those already recited, pertinent to our present purpose.

In the first place then, when the greater part of the Air had been pump'd out of the Receiver, the rising bubbles ascended so very slowly in the Pipe, that their Progress was scarce discernable; which seem'd to proceed from this, That their bigness [Page] was such, That they could not sufficiently extend themselves in the cavity of the Glass, without pressing on both hands against the sides of it, whereby they became of more difficult extrusion to the Water. And though it may seem strange that these bubbles should be of any considerable bulk, since 'tis like they consisted of lesser parcels of the Air lurking in the Water, than those that were vigorous enough to make their way through, long before them: yet they were commonly much larger than before, some of them being equal in quantity to four or five Peas: whether this their increase of bulk proceeded from the greater decrement of the pressure of the Air, or from the Union of two or three of those numerous bubbles which were then generated below the bottom of the Pipe, where we could not see what was done among them.

Another thing we noted in our bubbles was, That whereas in ordinary ones the Air, together with the thin film of Water that invests and detains it, is wont to swell above the surface of the Water it swims on, and commonly to constitute Hemispherical Bodies with it, the little parcels of Air that came up after the Receiver was pretty well empty'd, did not make protuberant bubbles, but such whose upper surface was either level with, or beneath that of the Water, so that the upper surface being usually somewhat convex, the less protuberant parts of it had a pretty quantity of Water remaining above them.

We also farther observ'd, that whereas in the bubbles that first appear'd in the Pipe, the ascending Air did, as in other common bubbles, make its way upwards, by dividing the Water through which it pass'd, in those bubbles that appear'd at the latter end of our Experiment, when the pressure of the little external Air, remaining in the Receiver, was grown inconsiderable, the ascending parcels of Air having how little more than the weight of the incumbent Water to surmount, were able both so to expand themselves as to fill up that part of the Pipe which they pervaded, and by pressing every way against the sides of it, to lift upwards with them what Water they found above them, without letting any considerable quantity glide [Page] down along the sides of the Glass; So that sometimes we could see a bubble thrust on before it a whole Cylinder of Water of perhaps an Inch high, and carry it up to the top of the Pipe; though as we formerly noted, upon the letting in the external Air, these tumid bubbles suddenly relaps'd to their former inconspicuousness.

All these things laid together seem'd sufficiently to confirm that, which the consideration of the thing it self would easily enough perswade, namely, That the Air, and such like Bodies being under Water, may be press'd upon as well by the Atmosphere, as by the weight of the incumbent Water it self.

Hence likewise we may verify what we observ'd at the close of the foregoing Experiment, namely, That from the sole swelling of Water there recorded, it cannot be so safely concluded, that Water, when freed from compression, is endow'd with an Elastical power of expanding it self: since thereby it appears that the Intumescence produc'd by that Experiment, may, (at least in great part) be ascribed to the numerous little bubbles which are wont to be produc'd in Water, from which the pressure of the Atmosphere is in great measure taken off. So apt are we to be mis-led, even by Experiments themselves, into Mistakes, when either we consider not that most Effects may proceed from various Causes, or mind onely those Circumstances of our Experiment, which seem to comply with our preconceiv'd Hypothesis or Conjectures.

And hence it seems also probable, that in the Pores or invisible little recesses of Water it self there lie commonly interspers'd many parcels of either Air, or at least something Analagous thereunto, although so very small, that they have not been hitherto so much as suspected to lurk there. But if it be demanded how it appears that there is interspers'd through the Body of Water any substance thinner than it self, and why that which produc'd the bubbles abovemention'd should not be resolutely said to be nothing else than a more active and spirituous part of the Water, we shall, in order to the Elucidation of this matter, subjoyn to what was formerly deliver'd the following Experiment.

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EXPERIMENT XXII.

WE recited in our ninteenth Experiment, how by drawing most of the Air out of the Receiver, we made the Water subside by degrees in a Glass not four Foot long: We shall now add, that in the like Experiment made in such a Tube, or a greater, it may be observ'd, That when the Water begins to fall, there will appear store of bubbles fasten'd all along to the sides of the Glass; of which bubbles, by the agitation of the Vessel consequent upon pumping, there will arise good numbers to the top of the Water, and there break; and as the Cylinder of Water is brought to be lower and lower, so the bubbles will appear more numerous in that part of the Tube which the Water yet fills; and the nearer the surface of the Water, in its descent, approacheth to these bubbles, the greater they will grow, because having the less weight and pressure upon them, the expansion of that Air which makes them, can be the less resisted by the pressure of the incumbent Water and Air; as seems probable from hence, that upon the letting in a little external Air, those bubbles immediately shrink.

It may indeed, as we lately intimated, be conjectur'd, that these bubbles proceed not so much from any Air pre-existent in the Water, and lurking in the Pores of it, as from the more subtle parts of the Water it self; which by the expansion allow'd them upon the diminish'd pressure of the ambient Bodies may generate such bubbles. And indeed, I am not yet so well satisfied that bubbles may not (at least sometimes) have such an origination: but that which makes me suspect that those in our tryals contain real Air, formerly latitant in the Pores of the Water, is this, That upon the inletting of the external Air, the Water was not again impell'd to the very top of the Tube whence it began to fall, but was stopt in its ascent near an Inch beneath the top. And since, if the upper part of the Tube had been devoid of any other than such Ethereal matter as was subtle enough freely to penetrate the pores of the Glass, the external Air would have been able to impel the Water to [Page] the top of a Tube seven or eight times as long as ours was; The Phaenomenon under consideration seem'd manifestly to argue, that the many bubbles that broke at the top of the Water, did contain a real Air, which being collected into one place, and hinder'd by the top of the Glass from receding, was able to with stand the pressure of the outward Air. As we see that if never so little Air remain in the Tube upon the making the Experiment De Vacuo with Quick-silver, no inclining of the Tube, (though a long one, will enable a Man to impell the Mercury up to the very top, by reason (as we formerly noted) of the resistance of the included Air, which will not be compress'd beyond a certain degree.

But in order to a farther discovery what our bubbles were, we will, on this occafion, inform Your Lordship, that we try'd the XIXth Experiment in one of our small Receivers, and found, that upon the drawing down of the Water, so many bubbles disclos'd themselves, and broke into the upper part of the Tube, that having afterwards let in the external Air, the Water was not thereby impell'd to the top of the Tube (three Foot in length) within a little more than half an Inch. And whether or no it were Air that possess'd that space at the top of the Tube which was not fill'd with Water, we took this course to examine. We drew the second time the Air out of the Receiver, and found, that by reason of the body that possess'd the top of the Tube, we were able not onely to make the Water in the Tube fall to a level with the surface of the Water in the Vessel; But also (by plying the Pump a little longer) a great way beneath it: which, since it could not well be ascrib'd to the bare subsiding of the Water, by reason of its own weight, argued that the Water was depress'd by the Air: which was confirm'd by the Figure of the surface of the Water in the Tube, which was much more concave than that of Water in Tubes of that bigness useth to be. And this farther tryal (to add that upon the bye) we made at the same time, That when the Water in the Pipe was drawn down almost as low as the Water without it, we observ'd, that (though we desisted from pumping) by the [Page] bare application of a hand moderately warm to the deserted part of the Tube, the remaining Water would be speedily and notably depress'd. And having for a while held a kindled Coal to the outside of the Tube, (the Pump being still unimploy'd, because the Vessel chanced to hold extraordinarily well) the Air was by the heat so far expanded, that it quickly drove the Water to the bottom of the Tube, which was divers Inches beneath the surface of the ambient Water. Whereby it appears (by the same way by which we formerly measur'd the dilatation of the Air) that the Air, even when it is expanded to between 90 and 100 times its extent, will yet readily admit of a much farther rarefaction by heat.

I consider'd also that in case the Bubbles we have been speaking of, were produc'd by the parcels of Air latitant in the Water, that Air being now got together to the top of the Tube, though the Air were again drawn out of the Receiver, the taking off its pressure would not disclose bubbles as before; and accordingly, the Air being again pump'd out, the Water in the Tube descended as formerly: but for a great while we scarce saw one bubble appear, onely when the Receiver had been very much exhausted; and the Water was fallen very low, there appear'd near the bottom of the Tube, certain little bubbles, which seem'd to consist of such parcels of Air as had not, by reason of their smallness, got up to the top of the Water, with the more bulky and vigorous ones. And that which is not inconsiderable, is, That having, by letting in the Air, forc'd up the Water into the Tube, we could not perceive that it ascended near the top, though we permitted the Engine to remain unimploy'd for two or three Nights together, and watch'd whether the Water would swell up and fill the Tube. And on this occasion I remember, that having try'd such an Experiment as this with Quick-silver instead of Water, in a Tube of about a Foot and a half long, wherein it might seem more hopefull to escape bubbles; yet upon the drawing down the Quick-silver as low as we could, and letting in the external Air upon it, we found that some lurking particles of Air were got up to the top [Page] of the Tube, and hinder'd the Quick-silver from being forc'd up again so high. And though the Quick-silver were by this means brought to appear a very close and lovely Metalline Cylinder, not interrupted by interspers'd bubbles as before; yet having caus'd the Air to be again drawn out of the Receiver, I could perceive several little bubbles to disclose themselves, fasten'd to the inside of the Tube, near the bottom of it; and having purposely watch'd one or two of the chiefest, I had the pleasure to observe, that though they grew bigger and bigger as the surface of the Mercurial Cylinder fell nearer and nearer to them, so as that at length they swell'd into a conspicuous bulk; yet upon the wary letting in the Air upon them, they did not break, but presently shrunk up into a littleness that render'd them inconspicuous.

Whence it seems very probable, if not certain, that even in the closest and most ponderous Liquors, and therefore much more in Water, there may lurk undiscernable parcels of Air, capable, upon the removal of the pressure of the ambient Air (though but in part) and that of the liquor wherein it lurks, to produce conspicuous bubbles. And consequently, if it seem inconvenient to admit an Elastical power in the Water, it may be said that the swelling of the compress'd Water in the Pewter Vessel lately mention'd, and the springing up of the Water at the hole made by the Needle, were not the effects of any internal Elater of the Water, but of the spring of the many little particles of Air dispers'd through that Water, and acting upon it in their sudden recovering themselves to a greater extent, than that to which a violent compression had reduc'd them to.

But though, from all these particulars, it seems manifest that the Bubbles we have been all this while treating of, were produc'd by such a substance as may be properly enough call'd Air; yet till we shall have had the opportunity of making some farther tryals concerning the nature of the Air, we shall not resolutely determine whether or no Air be a Primogenial Body (if I may so speak) that cannot now be generated or turn'd either [Page] into Water or any other Body. Yet in the mean while (because it is an important Question, and if rightly determin'd, may much conduce to the knowledge of the nature of the Air) we think it not unfit to make a brief mention of some of the particulars which at present occur to our thoughts in favor of either part of the Question.

First then, divers Naturalists esteem the Air (as well as other Elements) to be ingenerable and incorruptible. And reasons plausible enough may be drawn to countenance this Opinion from the consideration of that permanency that ought to belong to the corporeal Principles of other Bodies.

Next, Experience may be pleaded to the same purpose, for I have read of some who in vain attempted to turn Air into Water, or Water into Air.

The diligent Schottus tells us, that amongst other rarities to be met with in that great Repository of Schottus Mecham hydraulicopneumat. Part 3. Class. 1. them, the Musaeum Kercherianum, there is a round Glass with a tapering neck near half full (as one may guess by the Scheme he annexeth) of ordinary Spring-water, which having been hermetically shut up there by Clavius the famous Geometrician, the included Water is to this day preserv'd, not onely clear and pure, as if it were but newly put in: But (as it seems) without (in the least) turning into Air, notwithstanding its having been kept there these fifty years: For he tells us, That the Water hath continued there all this while without any diminution.

Nor doth it appear in those Glasses, which for Chymical Experiments we usually close with Hermes his Seal (as they call it) that the included Air doth, during its long imprisonment, notwithstanding the alteration it receiveth from various degrees of heat, discernably alter its nature. Whereas we plainly perceive in our Digestions and Distillations, that though Water may be rarefied into invisible Vapors, yet it is not really chang'd into Air, but onely divided by heat, and scatter'd into very minute parts, which meeting together in the Alembick or in the Receiver, do presently return into such Water as they constituted [Page] before. And we also see, that even Spirit of Wine, and other subtle and fugitive Spirits, though they easily fly into the Air, and mingle with it, do yet in the Glasses of Chymists easily lay aside the disguise of Air, and resume the divested form of Liquors. And so volatile Salts, as of Urine, Harts-horn, &c. though they will readily disperse themselves through the Air, and play up and down in the capacity of an Alembick or a Receiver: yet will they, after a while, fasten themselves to the insides of such Glasses in the form of Salts.

Besides, since Air is confessedly endow'd with an Elastical power that probably proceeds from its Texture, it appears not, what it is, that in such light alterations of Water, as are by many presum'd capable of turning it into Air, can be reasonably suppos'd so to contrive the Particles of Water, as to give them, (and that permanently,) the structure requisite to a Spring. I add the word permanently, because the newly mention'd observations seem to argue the Corpuscles of Air to be irreducible into Water, whereas the Aqueous Particles may perhaps for a while be so vehemently agitated, as to press almost like Springs upon other Bodies; yet upon the ceasing of the agitation, they quickly, by relapsing into Water, disclcse themselves to have been nothing else whilst they counterfeited the Air.

Lastly, The Experiment formerly made in our Engine with a piece of Match, seems to evince, that even those light and subtle Fumes (for the most part not aqueous neither) into which the Fire it self shatters dry Bodies, have no such Spring in them as the Air, since they were unable to hinder or repress the expansion of the Air included in the Bladder they surrounded.

I remember indeed that the Learned Josephus Acosta, in his History of the West Indies, tells us, Natural and Moral Hist. of the Indies. Lib. 3. c. 9. That he saw in those parts some Grates of Iron so rusted and consum'd by the Air, that the Metal being press'd between the Fingers, dissolv'd (to use his words) to powder, as if it had been Hay or parched Straw. And I remember too, that the Accurate Varenius Geogr. General. Lib. 1. cap. 19. tells us, That in the Islands commonly called Azores, [Page] the Air (and Wind) is so sharp, that in a short time it frets not onely Iron Plates, but the very Tiles upon the Roofs of Houses, and reduceth them to dust. And I have elsewhere mention'd some recent Observations of this kind. But it may be said, That the abovemention'd Authors ascribe the recited effects chiefly to the Winds, and that, however the corrosion of the Iron and the Tiles may proceed not from the Air it self, or any of its genuine parts, but from some saline Corpuscles dispers'd through the Air, and driven by the Winds against the Bodies it is presum'd to fret. And that such volatile Salts may copiously ascend into the Air, and yet retain their nature, as doth the more fixt Salt in the Sea-water, the sublimations of Sal-Armoniack may sufficiently evince. Not to mention, that I have shewn some Friends a secret kind of saline Substance incomparably subtler than Sal-Armoniack, which did not onely easily enough ascend it self, but carried up with it (and that in a very great proportion) the solid and ponderous Body even of uncalcin'd Gold in the form of subtle exhalations, which did afterwards fasten themselves to the upper parts of the Vessels, and yet manifest themselves to continue Gold. We remember also, that to try whether Water could be turn'd into Air, we once took an AEolipile, into which we had before convey'd some Water, and placing it upon kindled Coals when the heat forc'd out a vehement stream of aqueous Vapors; we ty'd about the Neck of it, that of a Bladder, which we had before empty'd of Air; and finding the AEolipile after a while to blow up the Bladder, we carefully ty'd it again that the included substance might not get away. Then slipping it off from the AEolipile we convey'd it into our Receiver, to try whether or no that which in part distended the Bladder would appear by its Spring to be true Air: whereby we found that upon the exsuction of the ambient Air, the included substance expanded it self and the Bladder, to a very much greater bulk than it was of before. And for farther satisfaction, having again taken out the Bladder, we suffer'd it to remain ty'd up till next Morning, to try whether time, and the coldness of the Night, would make the [Page] contain'd substance relapse into Water: But the next Morning we found it little less tumid than before. I remember, I say, that I once made this Experiment; but I might say in answer to it, that the chief reason of my mentioning it, is, To let Your Lordship see, how requisite it is to be circumspect and considerate, when we are to make and to build upon nice Experiments. For though I may seem to have used sufficient caution, yet afterward considering with my self that the AEolipile I had imploy'd was a very large one, and that it required much more care than one that hath not try'd it would imagine, to drive out all the Air from a large AEolipile, I easily suspected that the distension of the Bladder in our pneumatical Vessel, might proceed not from the watery steams that came out at the narrow mouth of the AEolipile, and had very much wetted the Bladder, but from the rarefied Air which in that sort of Vessels is wont for a good while together to come out with the rarefied Water: and accordingly having reiterated the Experiment, I found it very difficult (by reason of the thrinking of the Bladders (upon their being heated) and of other impediments) to make it so accurately as to deduce from it, that Water may be rarefied into true Air.

Against the other four above-mention'd Considerations, we cannot spend time to frame Objections, but must forthwith proceed to the mention of those things that seem to argue that Air (at least such as produc'd our bubbles) may be generated of Water and other Bodies.

First then we have found by Experience that a vapid Air, or Water rarefied into Vapor, may at least for a while emulate the elastical power of that which is generally acknowledg'd to be true Air. For if you take a good AEolipile, with a moderately strong and slender Neck, and filling it with Water, lay it upon quick Coals, you may after a while observe so great a pressure by some of the parts contain'd in the AEolipile upon others, that the Water will sometimes be thrown up into the Air above three or four Foot high; and if you then take the AEolipile almost red hot from off the fire, you may perceive that the Water [Page] will for a longer time than one would easily imagine continue to be spouted out in a violent Stream. And if there remains but little Water in the AEolipile when 'tis taken very hot from the Fire, immersing the Neck of it into cold Water, you will find, that after it begins to suck in some Water, there will be made from time to time store of large bubbles in that Water wherein the Neck was plunged. Which bubbles seem manifestly to proceed from hence, that for a while the heat in the AEolipile continues strong enough to rarefy part of the Water that is suck'd in, and expel it in the form of Vapors through the Water incumbent on the Pipe. If also when the AEolipile is almost full of Water, and therefore can contain but little Air; you hold a Coal or Brand in that stream of Vapors that issues out of the narrow mouth of it, you will find this vapid or rorid Air, (if I may so call it) to blow the Fire very strongly, and with a roaring noise. And that it be not said that 'tis by the external Air which the aqueous steams drive before them, and not by the Steams themselves, that the Blast is made and the Flame excited; it hath been observ'd, that by approaching the Coal or Brand almost to the mouth of the AEolipile, the Wind appear'd more vehement, than if the Body to be kindled were held some Inches off.

But in regard the elastical power of the Stream, issuing out of an AEolipile, seems manifestly due to the heat that expands and agitates the aqueous Particles whereof that Stream consists, and that such rapid Winds seem to be but water scatter'd into little parts and set a-moving; since we find, that holding a Knife, or any solid, smooth, and close Body against the Stream that issues out of the AEolipile, the Vapors condensing upon it, will presently cover it with Water: It will be very pertinent to subjoyn a notable Experiment that I remember I have met with in the description given us by the Industrious Kircher, of several Musical Engines. And (though it may seem somewhat prolix) we will resite what he delivers in his own words, which are these.

[Page]Cum eodem tempore quo haec scripsi, summi Pont. Innocentii Xmi mandato organi hydraulici in horto Quirinali Kirch. Art. Mag. Con. & Disson. lib. 9. p. 309. constituendi cura mihi commendata esset, AEoliam cameram insigni sanè successu construi jussimus, eâ quae sequitur ratione.

Erat longitudo sive altitudo camerae AH 5 Pedum, Latitudine 3 ferè ex lateribus constructa; in See the fifteenth Figure. medio duo tenebat Diaphragmata CD & EF in modum cribri pluribus foraminibus pertusi. Paulo infra canalis G aquam advehens inserebatur in H eidem epistomium parabat exitum. Aqua itaque per canalem G maximo impetu ruens vehementissimum ventum mox intus excitabat; qui ventus nimiâ humiditate imbutus, ut purior exiret sicciórque, Diaphragmata illa in cribri modum pertusa, ordinata sunt. Intra haec enim aquae vehemens agitatio rupta fractáque Aerem puriorem per A canalem subtiliorémque emittebat: Verum cum postea inventum sit Aerem plus aequo humidum interioribus Organi meatibus maximum detrimentum inferre: Hinc, ut Aer aquosus ficcissimam consistentiam acquireret, ordinavimus canalem plumbeum QR in helicem contortum vasi S aliquantulum capaciori in modum Urnae efformato, insertum. Intra Urnam enim plumbeam & canalem tortuosum illisus Aer humidus, ita ab omni aquositate defaecabatur, ut ex furno in Organum derivatus dici potuerit. Urna S canalis tortuosi QR ultimum orificium Z inseritur anemothecae Organi. Et hunc modum Organis hydraulicis omnium aptissimum reperi.

Debet autem camera illa situari in loco quantum fieri potest sicciori, ita ut longo canali aqua intra eam derivetur, ne locus humiditate suâ Organis officiat.

Thus far the Ingenious Kircherus, whom I the rather cite, because although I have been informed of divers Ventiducts (as they call them) by very knowing Travellers that have observ'd them: yet this relation of our Author being very punctual, and deliver'd upon his own particular Experience, hath I confess, made me with I had had the good fortune when I was at Rome, to take notice of these Organs; or that I had now the opportunity [Page] of examining of such an Experiment. For if upon a strict enquiry I should find that the breath that blows the Organs doth not really upon the ceasing of its unusual agitation by little and little relapse into Water, I should strongly suspect that 'tis possible for Water to be easily turh'd into Air. I remember indeed, that we have formerly taught, that there lurks an interspersed Air in the pores of ordinary Water, which may possibly be struck out by the breaking of the Water in its fall into the AEolian Chamber, (as he calls it.) But in regard the Scheme seems to represent that Chamber as closely shut, and thereby forbids us to suppose that any Air is carried into it, but what is latitant in the Water, it will scarce seem probable (to him who remembers how small a proportion of Air, that appear'd to be when its rarefication ceased, which was conceal'd in the Water we freed from bubbles in our Receiver) that so little Air as is commonly dispers'd through Water, should be able, in so little Water as was requisite for so small a room, to make so vehement a Wind as our Author here tells us of. I have sometime therefore suspected, that in this case the Wind may be produc'd by small particles of the Water it self, forcibly expell'd out of the Chamber into the Organs. And to the Objection, to which I foresaw this ghess to be liable, namely, That, no heat intervening, there appear'd nothing that should raise the Water into exhalations, and give them an impulse. I thought it might be said, that motion alone, if vehement enough, may, without sensible heat, suffice to break Water into very minute parts, and make them ascend upwards, if they can no where else more easily continue their agitation. For I remember, that travelling betwixt Lyons and Geneva, I saw, not very far out of the way, a place where the River of Rhone, comeing suddenly to be straiten'd betwixt two Rocks, so near each other, that a Man may, (if my Memory fail me not) stand a stride upon both at once: that rapid Stream dashing with great impetuosity against its Rocky Boundaries, doth break part of its Water into such minute Corpuscles, and put them into such a motion, that Passengers observe at a good distance off, as it were a Mist arising [Page] from that place, and ascending a good way up into the Air. Such, I say, was my suspicion touching the Wind we have been considering, but it seems something odd that aqueous Vapors should, like a dry Wind, pass through so long and tortuous a Pipe of Lead, as that describ'd by our Authour, since we see in the Heads of Stills, and the Necks of AEolipiles, how quickly such Vapors are even by a very little cold recondensed into Water. But to this also something may be speciously reply'd; wherefore contenting my self to have mention'd our Author's Experiment as a plausible, though not demonstrative proof, that Water may be transmuted into Air. We will pass on to mention in the third place another Experiment, which we try'd in order to the same enquiry.

We took a clear glass Bubble (capable of containing by guess about three Ounces of Water) with a Neck somewhat long and wide, of a Cylindrical form; this we fill'd with Oyl of Vitriol and fair Water, of each almost a like quantity, and casting in half a dozen small Iron Nails, we stopt the mouth of the Glass (which was top full of Liquor) with a flat piece of Diapalma provided for the purpose, that, accommodating it self to the surface of the Water, the Air might be exquisitely excluded: and speedily inverting the Viol, we put the Neck of it into a small wide-mouth'd Glass that stood ready with more of the same Liquor in it, to receive it. As soon as the Neck had reach'd the bottom of the Liquor it was dipp'd into, there appear'd at the upper part (which was before the bottom) of the Viol a bubble, of about the bigness of a Pea, which seem'd rather to consist of small and recent Bubbles, produc'd by the action of the dissolving Liquor upon the Iron, than any parcel of the external Air that might be suspected to have got in upon the inversion of the Glass, especially since we gave time to those little Particles of Air which were carried down with the Nails into the Liquor to fly up again. But whence this first Bubble was produced, is not so material to our Experiment, in regard it was so small: For soon after we perceiv'd the Bubbles produc'd by the action of the Menstruum upon the Metal, ascending copiously to the [Page] Bubble already named, and breaking into it, did soon exceedingly encrease it, and by degrees depress the Water lower and lower, till at length the substance contain'd in these Bubbles possessed the whole cavity of the glass Viol, and almost of its Neck too, reaching much lower in the Neck than the surface of the ambient Liquor, where with the open-mouth'd Glass was by this means almost replenished. And because it might be suspected that the depression of the Liquor might proceed from the agitation whereinto the exhaling and imprison'd Steams were put, by that heat which is wont to result from that action of corrosive salts upon Metals, we suffered both the Viol and the openmouth'd Glass to remain as they were, in a Window, for three or four days and nights together; but looking upon them several times during that while, as well as at the expiration of it, the whole cavity of the glass Bubble, and most of its Neck, seem'd to be possess'd by Air, since by its spring it was able for so long to hinder the expell'd and ambient Liquor from regaining its former place. And it was remarkable, that just before we took the glass Bubble out of the other Glass, upon the application of a warm hand to the convex part of the Bubble; the imprison'd substance readily dilated it self like Air, and broke through the Liquor in divers bubbles, succeeding one another.

Having also another time try'd the like Experiment with a small Viol, and with Nails dissolv'd in Aquafortis, we found nothing incongruous to what we have now deliver'd. And this Circumstance we observ'd, that the newly generated Steams did not onely possess almost all the whole cavity of the Glass, but divers times without the assistance of the heat of my hand, broke away in large bubbles through the ambient Liquor into the open Air: So that these Experiments with corrosive Liquors, seem'd manifestly enough to prove, though not that Air may be generated out of the Water, yet that in general Air may be generated anew.

Lastly, To the foregoing Arguments from Experience we might easily subjoyn the Authority of Aristotle, and of (his [Page] Followers) the Schools who are known to have taught, that Air and Water being symbolizing Elements (in the quality of moisture) are easily transmutable into one another. But we shall rather to the foregoing Argument add this, drawn from Reason, That if, as Leucippus, Democritus, Epicurus and others, follow'd by divers modern Naturalists, have taught, that the difference of Bodies proceeds but from the various Magnitudes, Figures, Motions, and Textures of the small parts they consist of, all the qualities that make them differ, being deducible from thence) there appears no reason why the minute parts of Water, and other Bodies, may not be so agitated or connected as to deserve the name of Air. For if we allow the Cartesian Hypothesis, according to which, as we noted at the beginning of this Letter, the Air may consist of any terrene or aqueous Corpuscles, provided they be kept swimming in the interfluent Celestial Matter; it is obvious that Air may be as often generated as Terrestrial Particles, minute enough to be carried up and down, by the Celestial Matter, ascend into the Atmosphere. And if we will have the Air to be a congeries of little slender Springs, it seems not impossible, though it be difficult, that the small parts of divers Bodies may by a lucky concourse of causes be so connected, as to constitute such little Springs, since (as we note in another Treatise) Water in the Plants it nourisheth is usually contriv'd into springy Bodies, and even the bare alter'd position and connexion of the parts of a Body may suffice to give it a Spring that it had not before, as may be seen in a thin and flexible Plate of Silver; unto which, by some strokes of a Hammer, you may give a Spring, and by onely heating it redhot, you may make it again flexible as before.

These, My Lord, are some of the Considerations at present occurring to my thoughts, by which it may be made probable, that Air may be generated anew. And though it be not impossible to propose Objections against these, as well as against what hath been represented in favour of the contrary Doctrine; yet having already almost tired my self, and I fear more than almost tired Your Lordship with so troublesome an Enquiry [Page] after the nature of Bubbles, I shall willingly leave Your Lordship to judge of the Arguments alledged on either side, and I should scarce have ventur'd to entertain You so long concerning such empty things as the Bubbles, which have occasioned all this Discourse, but that I am willing to invite You to take notice with me of the obscurity of things, or the dimness of our created Intellects (which yet of late too many so far presume upon, as either to deny or censure the Almighty and Omniscient Creator himself) and to learn hence this Lesson, That there are very many Things in Nature that we disdainfully overlook as obvious or despicable, each of which would exercise our Understandings, if not pose them too, if we would but attentively enough consider it, and not superficially contemplate, but attempt satisfactorily to explicate the nature of it.

EXPERIMENT XXIII.

SInce the writing of the twenty first and twenty second Experiments (and notwithstanding all that hath been on their occasion deliver'd concerning Bubbles) we made some farther trials in prosecution of the same inquiry whereto they were designed.

We chose then, amongst those Glasses which Chymists are wont to call Philosophical Eggs, one that containing about nine Ounces of Water, had a Neck of half an Inch in Diameter at the top, and as we guest, almost an Inch at the bottom; which breadth we pitched upon for a reason that will by and by appear: then filling it up with common Water to the height of about a Foot and an half, so that the upper part remained empty, we shut it into the Receiver, and watch'd what would follow upon pumping, which proved that a great part of the Air being drawn out, the Bubbles began to discover themselves at the bottom and sides of the Glass; and increasing, as the Air was more and more drawn away, they did from time to time ascend copiously enough to the top of the Water, and there quickly break: but by reason that the wideness of the Glass allow'd them free [Page] passage through the Water, they did not appear as in the former Experiments to make it swell: The Water scarce ever rising at all above the mark affixt to its upper surface, when it was put in, and upon the return permitted to the outward Air, and consequently the shrinking in of the remaining bubbles, the Water seem'd to have lost of his first extent, by the avolation of the formerly interspers'd Air.

Being willing likewise to try whether distilled Water were, by having been divided into minute parts, and then re-united, more or less dispos'd to expand it self than Water not distill'd: We took out of our Laboratory some carefully distill'd Rain-water, and put about two Ounces of it into a round Glass-bubble, with a very small Neck (not exceeding the sixth part of an Inch in diameter) which we filled half way to the top, and then convey'd it into the Receiver; the issue was, that though we drew out more Air than ordinary, yet there appeared not the least intumescence of the Water, nor any ascending bubbles.

But suspecting that either the small quantity of the Water or the figure of the Vessel might have an interest in this odd Phaenomenon, we took the lately mentioned Philosophical Egg, and another not much differing from it; the former we fill'd up with distill'd Rain-water to the old mark, and into the latter we put a long Cylinder or Rod of solid Glass to straiten the cavity of the Neck by almost filling it up; and then pouring some distilled Water into that also, till it reach'd within some Fingers breadth of the top, the Eggs were let down into the Receiver. In this Experiment the Air was so far drawn forth, before there appeared any bubble in either of the Glasses, that the disparity betwixt this and common Water was manifest enough. But at length, when the Air was almost quite pump'd out, the bubbles began to disclose themselves, and to increase as the pressure of the Air in the Receiver decreas'd. But whereas in the first mentioned Philosophical Egg the bubbles were very small, and never able to swell the Water, that we took notice of, at all above the mark: In the other, whose Neck, as we lately [Page] said, was straitned, and their passage obstructed, great numbers of them, and bigger, fastned themselves to the lower end of the Glass-rammer (if we may so call it) and gather'd in such numbers between that and the sides of the Neek, that the Water swell'd about a Finger's breadth above the mark, though upon the admitting of the external Air it relapsed to the former mark, or rather fell somewhat below it. And although thereupon in the first named Vessel all the bubbles presently disappeared, yet in the other we observed, that divers remained fastned to the lower part of the Glass-rammer, and continued there somewhat to our wonder, for above an hour after, but contracted in their dimentions.

Moreover, having suffered the Glasses to remain above twenty four hours in the Receiver, we asterwards repeated the Experiment, to try what change the exsuction of the external Air would produce in the Water, after the internal and latitant Air had (as is above recited) in great measure got away in bubbles, and whether or no the Water would by standing re admit any new particles of Air in the room of those that had forsaken it. But though we exhausted the Receiver very diligently, yet we scarce saw a bubble in either of the Glasses, not with standing which, we perceiv'd the Water to rise about the breadth of a Barly-corn, or more, in the Neck of that Glass wherein the solid Cylinder had been put; the Liquor in the other Glass not sensibly swelling.

And lastly upon the letting in of the Air, the Water in the straitned Neck soon subsided to the mark above which it had swollen, which whether it ought to be ascrib'd to the same small expansion of the parts of the Water it self, or to the rarifaction of some yet latitant Air broken into such small particles, as to escape our observation, seems not easily determinable, without such farther tryals, as would perhaps prove tedious to be recited as well as to be made; though I was content to set down those already mentioned, that it might appear how requisite it is in nice Experiments to consider variety of Circumstances.

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EXPERIMENT XXIV.

AFter having thus discovered what operation the exsuction of the ambient Air had upon Water, we thought good to try also what changes would happen in other Liquors upon the like taking off the pressure of the external Air. We took then a glass Egg, somewhat bigger than a Turkey Egg, which had a long Neck or Stem of about a ⅓ part of an Inch in diameter; and filling it up with Sallet-oyl untill it reach'd above half way to the top of the Neck, we inclos'd it in the Receiver together with common Water in a resembling Vessel; that we might the better compare together the operation of the exsuction of the Air upon those two Liquors. The Pump being set on work, there began to appear bubbles in the Oyl much sooner than in the Water, and afterwards they also ascended much more copiously in the former Liquor than in the latter: Nay, and when by having quite tired the Pumper, and almost our own Patience, we gave over, the Bubbles rose almost (if not altogether) in as great numbers as ever, insomuch that none of the various Liquors we tried either before or since, seemed to abound more with Aerial Particles than did this Oyl. In which it was farther remarkable, that between the time it was set into the Receiver, and that, at which we could get ready to pump, it subsided notably (by ghess about half an Inch) below the mark it reached before it was put in.

After this express'd Oyl, we made tryal of a distill'd one, and for that purpose made choice of the common Oyl or Spirit (for in the Shops where it is sold, the same Liquor is promiscuously called by either name) of Turpentine, because 'twas onely of that Chymical Oyl, we had a sufficient quantity: which, being put into a small glass Bubble with a slender Neck, so as to fill it about two Inches from the top, did, upon the evacuating of the Receiver, present us with great store of bubbles, most of which rising from the bottom, expanded themselves exceedingly in their ascent, and made the Liquor in the Neck to swell so much by degrees, that at length it divers times ran [Page] over at the top: by which means, we were hindred from being able to discern upon the letting in of the Air, how much the subsidence of the Oyl below the first mark was due to the recess of the Bubbles.

Having likewise a mind to try whether, as strong a solution of Salt of Tartar in fair Water as could be made (we having then no Oyl of Tartar per deliquium at hand) though it be accounted, Quick-silver excepted, the heaviest of Liquors, would afford us any bubbles; we put in a glass Egg full of it at the same time, with other Liquors, and found that they did long yield store of bubbles before any discovered themselves in the Liquor of Tartar; and having pursued the Experiment, it appear'd, That of all the Liquors we made trial of, this afforded the fewest and smallest bubbles.

Spirit of Vineger being tried after the same manner, exhibited a moderate number of bubbles, but scarce any thing else worth the mentioning.

Nor could we in Red Wine, try'd in a glass Egg, take notice of any thing very observable. For though upon the exsuction of the Air the bubbles ascended in this Liquor, as it were in sholes, and shifted places among themselves in their ascent; yet the intumescence of the whole bulk of the Liquor was scarce at all sensible, the bubbles most commonly breaking very soon after their arrival at the top, where during their stay, they composed a kind of shallow froth, which alone appeared higher in the Neck of the Glass, than was the Wine when it was let down. Neither yet did Milk, conveyed into our Pneumatical Vessel, present us with any thing memorable save that (as it seem'd by reason of some unctuousness of the Liquor) the bubbles not easily breaking at the top, and thrusting up one another, made the Intumescence appear much greater than that of common Water.

We likewise conveyed Hens Eggs into the Receiver, but after the exsuction of the Air, took them out whole again. That which invited us to put them in, was, That (as perhaps we mention in other papers) we had among other Experiments [Page] of cold, made Eggs burst, by freezing them within doors with Snow and Salt: The Ice, into which the aqueous parts of the Egg were turned by the cold, so distending (probably by reason of the numerous bubbles wont to be observable in Ice) the outward parts of the Egg, that it usually crack'd the Shell, though the inner Membrane that involv'd the several Liquors of the Egg, because it would stretch and yield, remain'd unbroken. And hereupon we imagin'd that in our Engine it might appear, whether or no there were any considerable Spring, either in any of the Liquors, or in any other more spirituous substance included in the Egg.

We took also some Spirit of Urine, carelesly enough deflegmed, and put it into the same Glass (first carefully scour'd and cleansed) wherein we had put the Oyl olive above-mentioned We took also another Glass, differing from a Glass egg, onely in that its bottom was flat, and fill'd it up to about ⅔ of the Neck (which was wider than that of the Egg) with rectified Spirit of Wine.

We took also another Glass egg, and having fill'd it with common Water till it reached to the middle of the Neck, we poured to it of the same Spirit of Wine, till it reached about an Inch higher.

These three Glasses having marks set on them, over against the edges of the contain'd Liquors were put into the Receiver, and that beginning to be evacuated, the bubbles in all the three Liquors began to appear. The mixture of the Spirit of Wine and Water disclos'd a great store of bubbles, especially towards the top; but scarce afforded us any thing worth the remembring. The Spirit of Urine appear'd to swell near an Inch and an half above the mark; and besides that, sent forth store of bubbles, which made a kind of froth at the upper part of it. And above that spume, there appear'd eight or ten great bubbles one above another, in a very decent order, each of them constituting, as it were, a Cylinder of about half an Inch high, and as broad as the internal cavity of the Neck: So that all the upper part of the Neck (for these bubbles reach'd to the top) seem'd [Page] to be divided into almost equal parts by certain Diaphragmes, consisting of the coats of the bubbles, whose edges appeared like so many Rings suspended one above another.

In the Spirit of Wine there did arise a great multitude of bubbles, even till weariness did make us give over the Experiment. And in these bubbles two or three things were remarkable; as first, That they ascended with a very notable celerity: Next, That being arrived at the top, they made no stay there: and yet, notwithstanding the great thinness and spirituousness of the Liquor, did, before they broke, lift up the upper surface of it, and for a moment or two form thereof a thin film or skin which appeared protuberant above the rest of the superficies like a small Hemisphere. Thirdly, That they ascended streight up, whereas those produced at the lower part of the Vessel, containing the mixture of the Water and Spirit of Wine, ascended with a wavering or wrigling motion, whereby they described an indented Line. Lastly, it was observable in the Spirit of Wine (and we took notice of the like in the Oyl of Turpentine lately mentioned) that not onely the bubbles seemed to rise from certain determinate places at the bottom of the Glass, but that in their ascension they kept an almost equal distance from each other, and follow'd one another in a certain order, whereby they seem'd part of small Bracelets, consisting of equally little incontiguous Beads: the lower end of each Bracelet, being as it were, fastned to a certain point at the bottom of the Glass.

The Air being sparingly let into the Receiver, the great bubbles formerly mentioned as incumbent upon one another, in that Glass that contained the Spirit of Urine, were by orderly degrees lessened, till at length they wholly subsided. Notwithstanding the recess of so many bubbles as broke on the top of the Spirit of Urine, during all the time of the Experiment; yet it scarcely appear'd at all to be sunk below the mark: Nor did the mixture of Spirit of Wine and Water considerably subside. But that is nothing to what we observ'd in the Spirit of Wine, for not onely it conspicuously expanded it self in the Neck of the Vessel that contain'd it; notwithstanding the largeness of it, [Page] and that the Bubbles were wont to break at the top of it almost as soon as they arriv'd there: But upon the readmission of the external Air, the Spirit of Wine retain'd its newly acquired expansion. And though we let it alone for near an hour together, in expectation that it might subside; yet when we took it out, we found it still swell'd between a quarter and half an Inch above the mark; and although it was not easily imaginable how this Phaenomenon could proceed from any mistake in trying the Experiment, yet the strangeness of it invited me to repeat it with fresh Spirit of Wine. Which, swelling in the Neck as formerly, I left all night in the Receiver, allowing free access to the external Air at the Stop-cock, and the next day found it still expanded as before, save that it seem'd a little lower: which decrement perhaps proceeded from the avolation of some of the fugitive parts of so voiatile a Liquor. And for better satisfaction having taken out the Glass, and consider'd it in the open Air, and at a Window, I could not find that there was any remaining bubbles that could occasion the persevering and admir'd expansion.

EXPERIMENT XXV.

BEing desirous to discover what difference there might be as to gravity and levity, between Air expanded under Water, and it self before such expansion; we took two very small Viols, such as Chymical Essences (as they call them) are wont to be kept in, and of the size and shape expressed by the eighth Figure: into one of these we put so much of a certain ponderous Mercurial mixture (hapning to be then at hand) that the mouth being stopt with a little soft Wax, the Glass would just sink in Water and no more; this we let fall to the bottom of a widemouth'd Christal Jar, fill'd with about half a pint of common Water, and into the same Vessel we sunk the other Essenceglass unstop'd, with as much water in it as was more than sufficient to make it subside. Both these sunk with their mouths downwards, the former being about three quarters full of Air, the latter containing in it a bubble of Air that was guess'd to be [Page] of the bigness of half a Pea: This done, the wide mouth'd Glass was let down into the Receiver, and the way of employing the Engine was carefully made use of.

The success was, That having drawn out a pretty quantity of Air, the bubbles began to disclose themselves in the Water, as in the former Experiments; and though for a good while after the bubbles ascended in swarms from the lower parts of the Water, and hastily broke at the top; yet we prosecuted the Experiment so long without seeing any effect wrought upon the Essence-bottles, that we began to despair of seeing of them rise. But continuing to ply the Pump, that little Glass, whose mouth was open'd, came to the top of the Water, being, as it were, boy'd up thither by a great number of bubbles that had fastned themselves to the sides of it; swimming thus with the mouth downward, we could easily perceive that the internal Air abovemention'd had much dilated it self, and thereby seem'd to have contributed to the emerging of the Glass, which remain'd floating, notwithstanding the breaking and vanishing of most of the contiguous bubbles: being hereby incouraged to persist in pumping, we observed with some pleasure, that at each time we turn'd the Key, the Air in the little Glass did manifestly expand it self and thrust out the Water, generally retaining a very protuberant surface where it was contiguous to the remaining Water. And when after divers exsuctions of the Air in the Receiver, that in the Viol so dilated it self as to expel almost all the Water, it turn'd up its mouth towards the surface of the Water in the Jar, and there deliver'd a large bubble, and then relapsed into its former floating posture. And this Experiment taught us, among other things, that it was a work of more time and labour than we imagin'd, to exhaust our Engine as much as it may be exhausted: for although before the emerging of the small Viol, we did (as hath been touch'd already) think we had very considerably emptied the Receiver, because there seem'd to come out but very little or almost no sensible Air at each exsuction into, and out of the Cylinder; yet afterwards, at each drawing down the Sucker, the Air included in the Viol [Page] did manifestly dilate it self, so long, that it did no less than nine times turn its mouth upwards, and discharge a bubble by conjecture about the bigness of a Pea, after the manner newly recited. But as for that Viol which had the weight in it, it rose not at all. So that being not able by quick pumping to gain another bubble from the Air in the swimming Glass, which proceeded from some small leak in the Vessel, though it held in this Experiment more stanch than was usual, we thought fit to let in leasurely the Air from without, upon whose admission that within the Viol shrinking into a very narrow compass, the Glass did, as we expected, fall down to the bottom of the Jar.

But being desirous before we proceed to any new Experiment, to try once more whether the little Glass, that had the weight in it, might not also be rais'd: After we had suffer'd the Engine to remain clos'd as it was, for five or six hours, the Pump was again ply'd with so much obstinacy, that not onely about the upper part of the Jar there appear'd a good number of bubbles (but very much smaller than those we saw the first time) but afterwards, there came from the bottom of the Jar, bubbles about the bigness of small Peas: which the Pump being still kept going, follow'd one another to the number of forty, coming from the stopp'd Viol; whose mouth, it seems, had not been shut so strongly and closely, but that the included Air, dilating it self by its own spring, made it self some little passage betwixt the Wax and the Glass, and got away in these bubbles; after which, the unstopt Glass began to float again, the Air shut up in it being manifestly so dilated as to expel a good part of the Water, but not so much as to break quite thorough. And at length, when our expectation of it was almost tired out, the heavier of the two Viols began to come alost, and immediately to subside again; which appear'd to be occasion'd by the Air within it, whose bulk and spring being weaken'd by the recess of the forty bubbles before-mention'd, it was no longer able, as formerly, to break forcibly through the incumbent Water; but forming a bubble at the mouth of the Glass, boyed it up towards the top; and there getting away, [Page] left it to sink again till the pressure of the Air in the Receiver being farther taken off, the Air in the Viol was permitted to expand it self farther, and to create another bubble, by which it was again for a while carried up. And it was remarkable, that though after having emptied the Receiver as far as well we could, we ceased from pumping; yet the Vessel continuing more stanch than it was wont, this ascent and fall of the Viol was repeated to the ninth time; the included Air, by reason of the smallness of the vent at which it must pass out, being not able to get away otherwise than by little and little; and consequently, in divers such parcels as were able to constitute bubbles, each of them big enough to raise the Viol and keep it alost untill the avolation of that bubble. Whereby it may appear, that the grand rule in Hydrostaticks, That a Body will swim in the Water, in case it be lighter than as much of the Water as equals it in bulk, will hold likewise when the pressure of the Atmosphere is in very great measure, if not when it is totally taken off from the Liquor and the Body: though it were worth inquiring what it is that so plentifully concurs to fill the bubbles made in our Experiment by the so much expanded Air. For to say with the old Peripatetick Schools, That the Air in rarefaction, may acquire a new extent, without the admission of any new substance, would be an account of the Phaenomenon very much out of date, and which, I suppose, our Modern Naturalists would neither give nor acquiesce in.

I know not whether it may be requisite to add, that in this Experiment, as in the former, the outward Air, being let in, did soon precipitate the floating Viol. But I think it will not be amiss to note, that (congruously to what hath been above recorded of the vast expansion of the Air) the Water which in the heavier Viol, succeeded in the room of those forty odd, if not fifty great bubbles of Air, which at several times got out of it, amounted but to a very inconsiderable bigness.

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EXPERIMENT XXVI.

IT having been observ'd by those that have consider'd what belongs to Pendulums (a Speculation that may, in my poor judgment, be highly usefull to the Naturalists) that their Vibrations are more slowly made, and that their motion lasts less in a thicker, than in a thinner Medium: We thought it not amiss to try if a Pendulum would swing faster, or continue swinging longer in our Receiver, in case of exsuction of the Air, than otherwise. Wherefore we took a couple of round and polish'd Pendulums of Iron or Steel, of equal bigness, as near as we could get the Artificer to make them, and weighing each of them twenty Drachmes, wanting as many Grains. One of these we suspended in the cavity of the Receiver by a very slender silken string, of about seven Inches and a half in length from the Cover of the Receiver to which it is fasten'd. Then (by inclining the Engine) we made the Pendulum swing to and fro in it, and describe as long Arches as in the capacity of so brittle a Vessel we thought safe and convenient. And one of the Assistants telling the recursions of the other Pendulum hanging in the free Air, by a string of about the same length, we shortned and lengthned this other Pendulum, till it appear'd to keep the same pace in its Vibrations, with that shut up in the Receiver. Then having carefully drawn away the Air, we did again set the Pendulum in the Receiver a vibrating; and giving the other Pendulum such a motion as made it describe an Arch, according to ones ghess, equal to that of the included Pendulum; we reckon'd, one of us, the Recursions of that Pendulum which was swinging within the Receiver; and another of us, that which was moving in (that which one would think a much more resisting medium) the Air. But once, one of us reckon'd near two and twenty Recursions of the included Pendulum, whilst the other reckon'd but twenty of the Pendulum that vibrated without. And another time also, the former of these Pendula was reckon'd to have made one and twenty Recursions, wherein the other made but twenty; Yet this Experiment [Page] seem'd to teach us little, save that the difference betwixt the motion of such a Pendulum in the common Air, and in one exceedingly rarefied, is scarce sensible in Vessels no bigger than our Receiver; especially, since though during this Experiment it held very well, yet we could not suppose it to be altogether devoid of Air. We observed also, that when the Receiver was full of Air, the included Pendulum continued its Recursions about fifteen minutes (or a quarter of an hour) before it left off swinging; and that after the exsuction of the Air, the vibration of the same Pendulum (being fresh put into motion) appear'd not (by a minutes Watch) to last sensibly longer. So that the event of this Experiment being other than we expected, scarce afforded us any other satisfaction, than that of our not having omitted to try it. And whether, in case the trial be made with a Pendulum much less disproportionate to the Air than Steel is, the event will much better answer expectation, experience may be consulted.

EXPERIMENT XXVII.

THAT the Air is the medium whereby sounds are convey'd to the Ear, hath been for many Ages, and is yet the common Doctrine of the Schools. But this Received Opinion hath been of late oppos'd by some Philosophers upon the account of an Experiment made by the Industrious Kircher, and other Learned Men: who have (as they assure us) observ'd, That if a Bell, with a Steel Clapper, be so fasten'd to the inside of a Tube, that upon the making the Experiment De Vacuo with that Tube, the Bell remain'd suspended in the deferted space at the upper end of the Tube: And if also a vigorous Load-stone be apply'd on the outside of the Tube to the Bell, it will attract the Clapper, which upon the removal of the Load-stone falling back, will strike against the opposite side of the Bell, and thereby produce a very audible sound; Whence divers have concluded, That 'tis not the Air, but some more subtle Body that is the medium of sounds. But because we conceiv'd that, to invalidate such a consequence fro m this ingenious Experiment (though [Page] the most luciferous, that could well be made without some such Engine as ours) some things might be speciously enough alledg'd; we thought fit to make a trial or two, in order to the discovery of what the Air doth in conveying of sounds, reserving divers other Experiments triable in our Engine concerning sounds, till we can obtain more leasure to prosecute them. Conceiving it then the best way to make our trial with such a noise as might not be loud enough to make it difficult to discern slighter variations in it; but rather might be, both lasting, (that we might take notice by what degrees it decreas'd;) and so small, that it could not grow much weaker without becoming imperceptible. We took a Watch, whose Case we open'd, that the contain'd Air might have free egress into that of the Receiver. And this Watch was suspended in the cavity of the Vessel onely by a Pack-thread, as the unlikeliest thing to convey a sound to the top of the Receiver: And then closing up the Vessel with melted Plaister, we listen'd near the sides of it, and plainly enough heard the noise made by the ballance. Those also of us, that watch'd for that Circumstance, observ'd, that the noise seem'd to come directly in a streight Line, from the Watch unto the Ear. And it was observable to this purpose, that we found a manifest disparity of noice, by holding our Ears near the sides of the Receiver, and near the Cover of it: which difference seem'd to proceed from that of the Texture of the Glass, from the structure of the Cover (and the Cement) through which the sound was propagated from the Watch to the Ear. But let us prosecute our Experiment. The Pump after this being imploy'd, it seem'd that from time to time the sound grew fainter and fainter; so that when the Receiver was empty'd as much as it us'd to be for the foregoing Experiments, neither we, nor some Strangers that chanc'd to be then in the Room, could, by applying our Ears to the very sides, hear any noise from within; though we could easily perceive that by the moving of the hand which mark'd the second minutes, and by that of the ballance, that the Watch neither stood still, nor remarkably varied from its wonted motion. And to satisfy our [Page] selves farther that it was indeed the absence of the Air about the Watch that hinder'd us from hearing it, we let in the external Air at the Stop-cock, and then, though we turn'd the Key and stopt the Valve, yet we could plainly hear the noise made by the ballance, though we held our Ears sometimes at two Foot distance from the outside of the Receiver. And this Experiment being reiterated into another place, succeeded after the like manner. Which seems to prove, that whether or no the Air be the only, it is at least, the principal medium of Sounds. And by the way it is very well worth noting, that in a Vessel so well clos'd as our Receiver, so weak a pulse as that of the ballance of a Watch should propagate a motion to the Ear in a Physically streight Line, notwithstanding the interposition of so close a Body as Glass, especially Glass of such thickness as that of our Receiver: since by this it seems that the Air imprison'd in the Glass, must, by the motion of the ballance, be made to beat against the concave part of the Receiver, strongly enough to make its convex part beat upon the contiguous Air, and so propagate the motion to the Listners Ears. I know this cannot but seem strange to those, who, with an eminent Modern Philosopher, will not allow that a Sound, made in the cavity of a Room, or other place so clos'd, that there is no intercourse betwixt the external and internal Air, can be heard by those without, unless the sounding Body do immediately strike against some part of the inclosing Body. But not having now time to handle Controversies, we shall onely annex, That after the foregoing Experiment, we took a Bell of about two Inches in Diameter at the bottom, which was supported in the mid'st of the cavity of the Receiver by a bent stick, which by reason of its Spring press'd with its two ends against the opposite parts of the inside of the Vessel: in which, when it was clos'd up, we observed that the Bell seemed to sound more dead than it did when just before it sounded in the open Air. And yet, when afterwards we had (as formerly) emptyed the Receiver, we could not discern any considerable change (for some said they observ'd a small one) in the loudness of the sound. Whereby it [Page] seemed that though the Air be the principal medium of sound, yet either a more subtle matter may be also a medium of it, or else an ambient Body that contains but very few particles of Air, in comparison of those it is easily capable of, is sufficient for that purpose. And this, among other things, invited us to consider, whether in the above-mentioned Experiment made with the Bell and the Load-stone, there might not in the deserted part of the Tube remain Air enough to produce a sound: since the Tubes for the Experiment De Vacuo (not to mention the usual thinness of the Glass) being seldom made greater than is requisite, a little Air might bear a not inconsiderable proportion to the deserted space: And that also, in the Experiment De Vacuo, as it is wont to be made, there is generally some little Air that gets in from without; or at least store of bubbles that arise from the Body of the Quick-silver, or other Liquor it self, Observations heedfully made have frequently informed us: And it may also appear, by what hath been formerly delivered concerning the Torricellian Experiment.

On the occasion of this Experiment concerning sounds, we may add in this place, That when we tried the Experiment formerly mentioned, of firing Gun-powder with a Pistol in our evacuated Receiver, the noise made by the striking of the Flint against the Steel, was exceeding languid in comparison of what it would have been in the open Air. And on divers other occasions it appeared that the sounds created within our exhausted Glass, if they were not lost before they reach'd the Ear, seem'd at least to arrive there very much weaken'd. We intended to try whether or no the Wire-string of an Instrument shut up into our Receiver, would, when the ambient Air was suck'd out, at all tremble, if in another Instrument held close to it, but with out the Receiver, a string tun'd (as Musicians speak, how properly I now examine not) to an Unison with it, were briskly toucht, and set a Vibrating. This, I say, we purpos'd to try to see how the motion made in the Air without, would be propagated through the cavity of our evacuated Receiver. But when the Instrument wherewith the tryal was to be made came to [Page] be imploy'd, it prov'd too big to go into the Pneumatical Vessel: and we have not now the conveniency to have a fitter made.

We thought likewise to convey into the Receiver a long and slender pair of Bellows, made after the fashion of those usually employ'd to blow Organs, and furnished with a small Musical instead of an ordinary Pipe. For we hop'd, that by means of a string fastned to the upper part of the Bellows, and to the moveable stopple that makes a part of the Cover of our Receiver, we should, by frequently turning round that stopple, and the annexed string, after the manner already often recited, be able to lift up and distend the Bellows; and by the help of a competent weight fastned to the same upper part of the Bellows, we should likewise be able, at pleasure, to compress them: and by consequence, try whether that subtler matter than Air (which, according to those that deny a Vacuum, must be suppos'd to fill the exhausted Receiver) would be able to produce a sound in the Musical Pipe; or in a Pipe like that of ordinary Bellows, to beget a Wind capable to turn or set on moving some very light matter, either shap'd like the Sails of a Wind-Mill, or of some other convenient form, and exposed to its Orifice. This Experiment, I say, we thought to make, but have not yet actually made it for want of an Artificer to make us such a pair of Bellows as it requires.

We had thoughts also of trying whether or no, as Sounds made by the Bodies in our Receiver become much more languid than ordinary, by reason of the want of Air: so they would grow stronger, in case there were an unusual quantity of Air crouded and shut up in the same Vessel. Which may be done (though not without some difficulty) by the help of the Pump, provided the Cover and Stopple be so firmly fasten'd (by binding and Cement, or otherwise) to the Glass and to each other, that there be no danger of the condensed Airs blowing of either of them away, or its breaking through the junctures. These thoughts, My Lord, as I was saying, we entertain'd; but for [Page] want of leasure, as, of as good Receivers as ours, to substitute in its place, in case we should break it before we learn'd the skill of condensing the Air in it, we durst not put them in practice: Yet, on this occasion, give me leave to advertise Your Lordship once for all, That though for the reasons newly intimated, we have, Only in the seventeenth Experiment, taken notice, that by the help of our Engine the Air may be condens'd as well as rarefied; yet there are divers other of our Experiments, whose Phaenomena it were worth while to try to vary, by means of the compression of the Air.

EXPERIMENT XXVIII.

WE taught, among divers other things, when we discoursed of our first Experiment, That the Air shut up in our Receiver, presseth as strongly upon the Bodies shut up with it, as if they were exposed to the pressure of the whole Atmosphere. That this was not inconsiderately propounded, we hope Your Lordship hath gather'd from divers of the things already recited: But yet perhaps it will not be amiss to subjoin, by way of farther confirmation of the same truth, the following Experiment: which would have accompanied the 20th, but the Paper wherein the one was written chanced not to be at hand, when the other was sent away.

We convey'd into the Receiver a new Glass Viol, capable of holding about 6 or 7 ounces of Water, into which we had before put 2 or 3 Spoonfulls of that Liquor, and stopt it close with a fit Cork. The Pneumatical Vessel being emptyed, there appear'd not any change in the inclos'd Water, the Air imprisoned with it, not having the force to blow out the stopple. Which event, though it were no other than we expected, was differing from what we desir'd. For we would gladly have seen what change would have appeared in the Water upon the Bottles being suddenly unstopp'd, in a place where the ambient Body was so differing from our common Air. Wherefore we did again put in the Viol, but less strongly clos'd than formerly, though as strongly stopt as seem'd requisite on ordinary occasions: [Page] But when the Air was pumped out of the Receiver, that within the Viol did quickly, as we expected, find or make it self little passages to get out at: as we argued, from this, That whereas when the Viol was put in the time before, the Water remained all the while perfectly free from bubbles; at this time the bottom of the Glass appear'd all covered with them, and they, upon the egress of the excluded Air into the Receiver, did presently flag and shrink up.

From these trials it seem'd deducible enough, that whilst the Viol continued to be well stopt, the included Water did, from the Air, shut up with it, sustain a pressure equal to that of the Atmosphere; since till the Air could get out of the Glass, there appeared no bubbles in the Water, notwithstanding the want of pressure in the ambient Body.

But to be sure to reach the chief end of our Experiment, we made use of this other expedient: We caused a convenient quantity of Water to be put, and Hermetically shut up into a Glass Egg, whose long Neck (which was purposely made of an unequal thickness) was fastened to one end of a string, whose other end was tied to the Cover of our Receiver, after the manner elsewhere mentioned already: Then the Egg being conveyed into the Pneumatical Vessel, and that being evacuated, we did, by turning the brass Stopple formerly describ'd amongst the parts of our Engine, so shorten the string as to break the Glass; whereby liberty being given to the Air imprisoned in the Egg, to pass into the cavity of the Receiver, the sudden recess of the Air made the bubbles in a trice appear so numerous, and ascend so swiftly in the Water, that their motion look'd like that of a violent shower of Rain; save that the bubbles did not, like the drops of Rain, tend downwards, but upwards. Which made me resemble this Phaenomenon to what I have seen happen in the dissolution of Seed-Pearl in some acid Menstruum, inwhich, if a good quantity of the little Pearls be cast whole, they will at first, if the Menstruum be sharp enough, be carried in swarms from the bottom to the top of the Liquor. We will add, that without sealing up the Glass, this Experiment [Page] may be tryed in one of our smallest Receivers. For there the exsuction of the ambient Air may be performed so nimbly, that immediately the bubbles lurking in the Water are allowed to display themselves, and ascend in throngs; insomuch, as having in such a Receiver try'd the Experiment with Wine as a more spirituous Liquor) instead of Water, the Red-Wine appeared all cover'd, with a copious, but vanishing white Froth, almost as if a Vessel full of bottl'd drink had been unwarily opened.

EXPERIMENT XXIX.

IT may not a little conduce to the clearer explication of divers Points in the Doctrine of Meteors, and perhaps of some other Physiological difficulties, to discover what the Air doth to the motion of those Steams or Exhalations that ascend into it, namely, Whether they mount upwards by virtue of any such positive levity (as some Peripateticks speak) acquir'd together with their Aërial nature, as inables them to pierce through part of the Atmosphere, and over-come its resistance. Or else, whether these steams being once raised above the Earth by their agitation, have their ascent and sustentation aloft, rather promoted than hindred by the Air: as the inferior parts of that, being thicker and heavier than the superior, the steams can more easily continue for a while their agitation upwards than downwards; And afterwards are by the same fluidity and thickness of the Air, carried to and fro in it, and kept from relapsing to the Earth: as in the Sea-Water the saline parts are kept from subsiding by those aqueous ones wherewith they are associated.

We hop'd to illustrate this matter, by observing the motion of the smoke, proceeding from kindled or flaming Bodies in our exhausted Receiver. But as we formerly noted, upon the exsuction of the Air, the smoking of those Bodies presently ceas'd. We had thoughts also of conveying into our Pneumatical Glass a hot Iron, with some Bodie easie to be dissipated into smoke set upon it, but consider'd, that neither was that way free from inconveniencies; especially this, that the hot Body [Page] would make the Imprisoned Air circulate within the Receiver, and consequently make it questionable whether the ascent of the steams would not be due to the new and acquired motion of the Air.

Wherefore I bethought my self of another way to satisfie in some measure my curiosity, to wit, by means of a certain Liquor, which I call'd to mind that some years ago I had (for a design that belongs not to our present purpose) prepar'd; which, I suppose, I shew'd Your Lordship, and which had the luck to be taken notice of by divers very Ingenious and Famous Men. For this Liquor, though most of its Ingredients be Metals, and all of them ponderous enough, is yet of that nature, that whilst the Viol wherein it is kept is stopt (how slight a Cover soever) both the Liquor and the Glass are transparent; and so is that upper half of the Glass to which the Liquor reacheth not: But as soon as ever the stopple is taken out, and full access is given to the external Air, both the inward part of the Cork, and the Liquor it self, do presently send upwards, and scatter abroad asume as thick and white, as if there were a quantity of Alabaster-dust thrown up into the Air: And this smoaking of the Liquor lasts till my unwillingness to waste it invites me to stop it again, and then the ascension of the fumes suddenly ceaseth, till the Viol be again unstop'd.

This fuming Liquor then I thought would much conduce to the discovery I desir'd to make, since it sav'd me the need of conveying any hot Body with it into the Receiver, and would not darken it with fumes before the time. Wherefore having ty'd to the Viol a great weight of Lead, to keep it from being lifted up by the drawing out of the Cork; and having ty'd to the stopple one end of a string, of which the other end was made fast to the Cover of the Pneumatical Glass, the Liquor was carefully clos'd up after the wonted manner; then the Air being diligently pump'd out, the Viol was unstop'd in the empty'd Receiver. And though immediately, upon the drawing out of the Cork, there appear'd to be as it were thrown up some white fumes, which seem'd to proceed from the Air before imprison'd [Page] in the Viol, and diffusing it self suddenly into the capacity of the Receiver: Yet we afterward observ'd, as we expected, That the fumes did not amount and disperse themselves as they used to do in the open Air; but that, when by reason of the agitation of the Corpuscles of the Liquor, which could not continue their motion in so narrow a space as the Viol afforded them, and were therefore reduc'd to thrust one another out of it; when, I say, by these assistances the fumes were ascended to the lip of the Viol, they mounted no higher, but ran down along the outside of the Viol to the bottom of it; and thence along, a long and inclining piece of Lead, on which the Viol rested, like a little Stream (not very much bigger than a Swans Quill) whose nature they seem'd to emulate so well, that it quitted not the Viol till it was come to the bottom of it, and then forsook it in such a manner'a as stream of Water of the same bigness would have done. And this stream lasted a pretty while, and would probably have lasted longer, but that being loath to waste my Liquor, I let in at the Stop-cock a pretty deal of the external Air; notwithstanding which, finding after a while that the stream did run afresh, though, as it seem'd not altogether so copious as before; I let as much more Air, as would come in: and found (somewhat to my wonder) that though the stream formerly mention'd dis-appear'd, yet there appear'd not any white fumes to arise, either from the Cork, or out of the Viol it self, no not when the Cover was remov'd from the Receiver; though not only after a while there ascended white fumes from the Receiver: but having forthwith taken out the Viol into the open Air, it emitted white exhalations as before; and having presently after unstopp'd it in an open Window, we found both it and the Cork immediately to send forth a yet much more plentifull smoak: Though it be now divers years since this Numerical Liquor was prepared, after the manner mention'd either by Carneiades or Eleutherius (for I do not well remember which) in those Dialogues concerning Heat and Flame that have above been mention'd.

More circumstances concerning these Fumes we might have observ'd, had we not been deterr'd by an Indisposition in point [Page] of health, from having much to do with steams of so dangerous a nature, as by that of the Ingredients of this Liquor these seem likely to be of.

The reflexions that may be made upon this Experiment, we have not now the leasure to prosecute, and therefore shall content our selves to recommend the several circumstances of it to Your Lordship's serious consideration; and to take notice (en passant) that steams in an ambient Body, or a medium thinner than themselves, may both tend downwards, and otherwise emulate the nature of a Liquor; which I therefore point at, that it may appear the less strange, if we sometimes speak of the Atmosphere as of a kind of Liquor, in comparison of that more thin and subtle Celestial matter that surrounds it.

And though it might perchance suffice to have on this occasion intimated thus much; yet, lest this way of speaking of the Atmosphere should be thought too bold and extravagant, I am content to borrow an Experiment of the discourse formerly mention'd (touching fluidity and firmness) and subjoyn it here with alterations suitable to the contrivance of our Engine; and this the rather, because I hope it may conduce to the discovery of the nature of the Atmosphere: for which reason it might have been annext to what hath been noted either upon the first, or eighteenth Experiment, but that when they were written and sent away, it came not into my mind. The Experiment then as we try'd in our Engine, was as follows.

EXPERIMENT XXX.

WE took one of the small Receivers, often mention'd already, and into it we convey'd a piece of well lighted Match; and letting it remain there till it had fill'd the Receiver with smoak, we took it out and hastily clos'd again the Receiver, that the smoak might not get away. Then staying awhile to let these fumes leisurely subside, we found, as we expected, that after some time they setled themselves in the lower half of the Receiver; in a darkish Body, leaving the upper half of the Receiver transparent, and as to sight, full of nought but clear [Page] Air. Now to manifest that this smoak thus setled emulated a Liquor, we inclin'd the Engine that contain'd it, sometimes to one side, and sometimes to the other; and observ'd the smoak to keep its surface almost Horizontal, notwithstanding the stooping of the Vessel that held it, as Water, or another liquor would in the like case have done. And if by a quicker rocking of the Engine the smoak were more swiftly shaken, it would, like Water, either vibrate to and fro from one side to the other of the Glass, or else have its surface manifestly curl'd with Waves, but preserve its self in an entire and distinct Body from the incumbent Air; and being permitted to rest a while, would soon recover its former smooth and level Superficies. If also the Key were turn'd and the Valve unstopp'd, so that there was a free, though but a narrow passage open'd betwixt the external Air and the cavity of the Receiver, then would some of this smoak fall down, as it were, in a stream into the subjacent Cylinder, and a proportionate quantity of the outward Air, would manifestly ascend through it into the incumbent Air, much after the same manner as if you invert a Viol with a long neck, and well fill'd with Red-Wine, into a Glass full of fair Water, you shall see the Water and Wine by degrees mingle with one another; the one falling down as it were in little colour'd streams, and the other ascending in its room in the like curled streams, sometimes preceded by round parcels of Water, which, by reason of their transparency, look almost like bubbles. The other circumstances of this Experiment, belonging not all of them to our present purpose, we shall content our selves with taking notice of one which seems the most important, and may illustrate and confirm some things formerly delivered. And it was, That if, when the superficies of our smoak lay smooth and Horizontal, a hot Iron were held near the outside of the Receiver, the neighbouring part of the included fumes (for the rest did not very much alter their former superficies) being rarified by the heat, would readily ascend in a large Pillar of smoak to the very top of the Receiver, yet without seeming to lose a distinct superficies, or to be confounded with Air; below which, upon the recess of [Page] the adventitious heat that by agitating it impell'd it upward, it would again subside.

All which being added to the late Experiment of the smoaking Liquor, and to what may be from that which hath been elsewhere said, gather'd to the same purpose, will, I hope, keep it at least from appearing absur'd. If, since we see that there is so great an inequality in the density and weight of Liquors, that Water is near fourteen times thinner or lighter than Quick-silver of the same bulk; and well dephlegm'd spirit of Wine, yet much lighter than Water, we venture to speak sometimes of the Atmosphere, as if it were a peculiar kind of thin and halitious Liquor (if I may so call it) much lighter than Spirit of Wine.

To these things I know not whether it will be requisite to add, That as we lately took notice of conspicuous Waves that appear'd upon the superficies of our agitated smoak: So some such thing may not absurdly be conjectur'd to happen on the superficies of the Atmosphere, by those strange ruggednesses that appear (especially in the Spring and Fall, when Exhalations and Vapours are wont to ascend most plentifully) upon the limb or edge of the Rising and Setting Sun. I speak thus disfidently upon this occasion, because I know, that by the Fluctuation or Boyling of the Suns own superficies, divers eminent Mathematicians have plausibly enough (but how truly, I leave Your Lordship to judge) endeavour'd to give an account of it. But if we will joyn with those that have ascrib'd of late this Phaenomenon, to the refraction the Sun-beams suffer in our vapid air, we may, as hath been intimated, promote their Doctrine, by deducing from it, That probably the surface of the Atmosphere is oftentimes (if not always) exceedingly curl'd or wav'd. And certainly it is somewhat wonderfull, as well as very pleasant to behold, how, to him that looks upon the setting Sun through a long and excellent Telescope, there will not only appear strange inequalities in the edge of it (insomuch that I have often seen it more indented than a Saw) but those inequalities will vanish in one place, and presently appear in another, and seem perfectly to move like Waves succeeding and destroying [Page] one another, save that their motion oftentimes seems to be quickest; as if in that vast Sea they were carried on by a Current, or at least by a Tide. And this (as we elsewhere note) appears to the Eye, not only when it looks directly through the Telescope upon the Sun; but also when a large and well defin'd Image of the Sun is by the same Telescope brought into a Room and cast upon a sheet of white Paper. But to insist on this were to digress: and therefore I will proceed to Experiments of another kind.

EXPERIMENT XXXI.

IT hath been admir'd by very ingenious Men, that if the exquisitely polish'd surfaces of two flat pieces of Marble, be so congruous to each other, that from their mutual application there will result an immediate contact, they will stick so fast together, that he that lifts up the uppermost, shall, if the undermost be not exceeding heavy, lift up that too, and sustain it alost in the free Air. A probable cause of this so close adhesion, we have elsewhere endeavoured to deduce from the unequal pressure of the Air upon the undermost stone; For the lower superficies of that stone being freely expos'd to the Air, is press'd upon by it, whereas the uppermost surface, being contiguous to the superior stone, is thereby defended from the pressure of the Air; which consequently pressing the lower stone against the upper, hinders it from falling, as we have elsewhere more fully declar'd. Upon these grounds we conjectur'd, that in case we could procure two Marbles exactly ground to one another, and in case we could also sufficiently evacuate our Receiver; the lower stone would, for want of the wonted and sustaining pressure of the Air, fall from the upper. But the farther trial of this Experiment we must, unless Your Lordship think it worth Your making at Paris, put off till a fitter opportunity. For where we now are, we cannot procure Marbles so exactly ground, that they will sustain one another in the Air above a minute or two, which is a much shorter time than the emptying of our Receiver requires. We did indeed try to make our Marbles stick close together, by moistening their polish'd surfaces [Page] with rectifi'd spirit of Wine, in regard that liquor, by its sudden avolation from Marble, if pour'd thereon, without leaving it moist or less smooth, seem'd unable to sustain them together after the manner of a glutinous Body, and yet seem'd sufficient to exclude and keep out the Air. But this we try'd to little purpose, for having convey'd into the Receiver two black square Marbles (the one of two Inches and a third in length or breadth, and somewhat more than half an Inch in thickness: The other of the same extent, but not much above half so thick) fasten'd together by the intervention of pure spirit of Wine; and having suspended the thicker by a string from the cover, we found not that the exsuction of the ambient Air would separate them, though a weight amounting to four Ounces were fasten'd to the lowermost Marble to facilitate its falling of.

I would gladly have the Experiment try'd with Marble, so well polish'd, as to need no Liquor whatsoever to make them cohere, and in a Vessel out of which the Air may be more persectly drawn than it was out of ours. But in the mean time, though we will not determine whether the spirit of Wine did contribute to the strong cohesion of these stones, otherwise than by keeping ev'n the subtlest parts of the Air from getting in between them: yet it seemed that the not falling down of the lowermost Marble, might, without improbability, be ascrib'd to the pressure of the Air remaining in the Receiver; which, as we formerly noted, having been able to keep a Cylinder of Water, of above a Foot in height, from falling to the bottom of the Tube, may well enough be suppos'd capable of keeping so broad a flat Marble from descending. And though this may seem a strange proof of the strength of the spring of the Air, ev'n when rarefied, yet it will scarce seem incredible to him that hath observ'd how exceeding strong a cohesion may be made betwixt broad Bodies, only by their immediate touching one another. A notable instance of which, I met with in this short Narrative of the Learned Zucchius. Juveni (saith he) lacertorum suorum robur jactanti proposit a P. Nic. Zucchius apud Scbot. part. 1. Mec. Hydraulopneum. semel est lamina aerea, per ansam in medio extantem[Page]apprehensam elevanda è tabula marmorea, cui optime congruebat: qui primo tanquam rem ludicram puero committendam contempsit: tum instantibus amicis manum utrámque admovens, cum luctatus diu haerentem non removisset, excusavit impotentiam, objecta peregrini & potentissimi glutinis interpositione, quo fortissime copulante nequiret divelli; donec vidit ab alio per tabulam facilimè laminam deduci, & ad extrema productam, & actam in transversum inde deportari. But that we may learn from our, own Engine, that two Bodies, though they touch each other but in a small part of their surfaces, may be made to cohere very strongly, only by this, That the Air presses much more forcibly upon the inferiour superficies of the lowermost Body, than upon the upper surface of the same: We will hereunto annex the following Experiment, though out of the order wherein they were made.

EXPERIMENT XXXII.

I Remember I have, in a Discourse touching Fluidity and Firmness, made mention of my having, by the exsuction of the Air out of a Glass Vessel, made that Vessel take up, or suck up (to speak in the common Language) a Body weighing divers Ounces; but our Engine affording us the opportunity of making considerabler Experiments of that kind, We thought fit to make a further trial of the force of the Atmosphere's pressure upwards, after the following manner.

The Receiver having been exquisitely clos'd as we have often taught already, and the Air being in a good measure drawn out of it, it was remov'd from off the Pump: and to the lower branch of the Stop-cock, there was speedily apply'd a tapering Valve of brass, such as is described in the 9th Figure, made fit to go with its narrower end into the cavity of the branch, and to fill the Orifice of that cavity with its broader part. And that the Air might not get in at the little intervals, left here and there between the convex surface of the stopple and the internal edge of the branch, those intervals were stopt with a little Diachylon. And to the door, or, (if you please) that part of [Page] the Valve which was to move to and fro, and in this Experiment hung perpendicular to the Horizon, there was, at a button of brass belonging to the Valve, fasten'd a broad scale wherein weights were to be put. This done, the Key of the Stop-cock was turn'd, and the external Air beating like a forcible stream upon the Valve to get in there, it did suddenly both shut the Valve and keep it shut so strongly, that we had time to cast in divers weights one after another into the Scale; till at length the weight overpowering the pressure of the Atmosphere, drew down the Valve by the strings that tied the Scale to it, and gave liberty to the outward Air to rush into the Receiver. Though another time, when the Valve had but little weight hanging at it, being, by I know not what accident, drawn down beneath its former place, it was by the impetuous current of the outward Air suddenly impell'd up into it again, and kept there. But in the former Experiment it is remarkable, That though the Receiver were not well exhausted, and though it leak'd whilst the rest of the Experiment was in prosecution: and though the Valve whereon the Cylinder of the Atmosphere could press, were not above an Inch and a half in Diameter, yet the weight kept up by suction, or rather supported by the Air, (namely the Valve, the Scale and what was cast out of it,) being sent to be weigh'd, amounted to about ten of our common Pounds, consisting of sixteen Ounces a piece: So that we doubted not but that, had the Experiment been made with favourable circumstances, the Air endeavouring to press in at the Orifice of the Stop-cock, would have kept a very much greater weight from falling out of it; I say the Air, because we found, by trial purposely made, that neither the imperfect contact of the Valve and the Stop-cock, nor the Diachylon that was employ'd to fill up the little Crannies left betwixt them, were considerable in this Experiment. By which it may, among other things, appear, that I did not without cause in the above-named Discourse touching Fluidity and Firmness, ascribe a great force, even to such Pillars of. Air as may be supposed to begin at the top of the Atmosphere, and recoyling from the ground, to terminate on the Bodies on which [Page] they press: since in the present Experiment such a weight was supported by so slender a Cylinder of Air, rebounding from the Earth to the Valve whereon it did bear.

EXPERIMENT XXXIII.

BUt in regard we have not yet been able to empty so great a Vessel as our Receiver, so well as we can the Cylinder it self; our Pump alone may afford us a nobler instance of the force of the Air we live in, insomuch, that by help of this part of our Engine, we may give a pretty near ghess at the strength of the Atmosphere, computed as a weight. And the way may be this; First, the Sucker being brought to move easily up and down the Cylinder, is to be impelled to the top of it: Then the Receiver must be taken off from the Pump, that the upper Orifice of the Cylinder remaining open, the Air may freely succeed the Sucker, and therefore readily yield to its motion downwards. This done, there must be fasten'd to one of the Iron Teeth of the Sucker, such a weight as may just suffice to draw it to the bottom of the Cylinder. And having thus examin'd what weight is necessary to draw down the Sucker, when the Atmosphere makes no other than the ordinary resistance of the Air against its descent; the Sucker must be again forc'd to the top of the Cylinder, whose upper Orifice must now be exactly closed; and then (the first weight remaining) we easily may, by hanging a Scale to the above-mention'd Iron (that makes part of the Sucker) cast in known weights so long, till in spight of the reluctancy of the Atmosphere the Sucker be drawn down. For to these weights in the Scale, that of the Scale it self being added, the sum will give us the weight of a Column of Air, equal in Diameter to the Sucker, or to the cavity of the Cylinder, and in length to the height of the Atmosphere.

According to this method we did, since the writing of the last Experiment, attempt to measure the pressure of the Atmosphere, but found it more difficult than we expected, to persorm it with any accurateness; for though by the help of the Manubrium the Sucker moved up and down with so much ease, [Page] that one would have thought that both its convex surface, and the concave one of the Cylinder were exquisitely smooth, and as it were slippery; yet when the Sucker came to be moved onely with a dead weight or pressure (that was not (like the force of him that pumped) intended as occasion required) we found that the little rufnesses or other inequalities, and perhaps too, the unequal pressure of the Leather against the cavity of the Cylinder, were able, now and then, to put a stop to the descent or ascent of the Sucker, though a very little external help would easily surmount that impediment; and then the Sucker would, for a while, continue its formerly interrupted motion, though that assistance were withdrawn. But this discouragement did not deter us from prosecuting our Experiment, and endeavouring, by a carefull trial, to make it as instructive as we could. We found then that a Leaden Weight, of 28 pounds (each consisting of sixteen Ounces) being fastned to one of the teeth of the Sucker, drew it down closely enough, when the upper Orifice of the Cylinder was left open: though by the help of Oyl and Water, and by the frequent moving the Sucker up and down with the Manubrium, its motion in the Cylinder had been before purposely facilitated. This done, the upper Orifice of the Cylinder was very carefully and closely stopped, the Valve being likewise shut with its wonted Stopple well oyl'd, after the Sucker had been again impell'd up to the top of the Cylinder. Then to the precedent twenty eight pound, we added a hundred and twelve pounds more; which forcing down the Sucker, though but leisurely, we took off the twenty eight pound weight; and being unable to procure just such weights as we would have had, we hung on, instead of it, one of fourteen pound: but found that, with the rest, unable to carry down the Sucker. And to satisfie our selves, and the Spectators, that it was the resistance of the ambient Air that hinder'd the descent of so great a weight, after that we had try'd that upon unstopping the Valve, and thereby opening an access to the external Air, the Sucker would be immediately drawn down. After this, I say, we made this farther Experiment, That having by a Man's strength [Page] forcibly depress'd the Sucker to the bottom of the Cylinder, and then fastned weights, to the above-named Iron that makes part of that Sucker, the pressure of the external Air finding little or nothing in the cavity of the evacuated Cylinder to resist it, did presently begin to impell the Sucker, with the weights that clogg'd it, towards the upper part of the Cylinder; till some such accidental Impediment, as we formerly mention'd, check'd its course. And when that rub, (which easily might be,) was taken out of the way, it would continue its ascent to the top, to the no small wonder of those By-standers, that could not comprehend how such a weight could ascend, as it were, of it self; that is, without any invisible force, or so much as Suction to list it up. And indeed it is very considerable, that though possibly there might remain some particles of Air in the Cylinder, after the drawing down of the Sucker; yet the pressure of a Cylinder of the Atmosphere, somewhat less than three Inches in Diameter (for, as it was said in the description of our Engine, the cavity of the Cylinder was no broader) was able, uncompress'd, not only to sustain, but even to drive up a weight of an hundred and odd pounds: for besides the weight of the whole Sucker it self, which amounts to some pounds, the weights annexed to it made up an hundred and three pounds, besides an Iron Bar, that by conjecture weighed two pounds more; and yet all these together fall somewhat short of the weight which we lately mention'd, the resistance of the Air, to have held suspended in the cavity of the Cylinder.

And though (as hath been already acknowledg'd (we cannot peradventure, obtain by the recited means so exact an account as were to be wish'd, of what we would discover: Yet, if it serve us to ground conjectures more approaching to the Truth, than we have hitherto met with, I hope it will be consider'd (which a famous Poet judiciously says)

Est quoddam prodire tenus, si non datur ultra.

Peradventure it will not be impertinent to annex to the other circumstances that have been already set down concerning this [Page] Experiment, That it was made in Winter, in Weather neither Frosty nor Rainy, about the change of the Moon, and at a place whose latitude is near about 51 degrees and a half: For perhaps the force or pressure of the Air may vary, according to the Seasons of the Year, the temperature of the Weather, the elevation of the Pole, or the phases of the Moon; all, or even any of them seeming capable to alter either the height or consistence of the incumbent Atmosphere: And therefore it would not be amiss if this Experiment were carefully tried at several times and places, with variety of circumstances. It might also be tried with Cylinders of several Diameters, exquisitely fitted with Suckers, that we might know what proportion several Pillars of the Atmosphere bear to the weights they are able to sustain or lift up; and consequently, whether the increase or decrement of the resistance of the ambient Air, can be reduced to any regular proportion to the Diameters of the Suckers: These, and divers other such things which may be try'd with this Cylinder, might most of them be more exactly try'd by the Torricellian Experiments, if we could get Tubes so accurately blown and drawn, that the cavity were perfectly Cylindrical.

To dwell upon all the several Reflexions, that a speculative Wit might make upon this and the foregoing Experiment, (I mean the thirty third and thirty second) would require almost a Volume; whereas our occasions will scarce allow us time to touch upon three or four of the chief Inferences that seem deducible from them, and therefore we shall content our selves to point at those few.

And first, as many other Phaenomena of our Engine, so especially, the two lately mention'd Experiments, seem very much to call in question the received Opinion of the nature or cause of Suction. For it's true indeed, that when men suck, they commonly use some manifest endeavour by a peculiar motion of their Mouths, Chests, and some other conspiring parts, to convey to them the body to be suck'd in. And hence perhaps they have taken occasion, to think that in all Suction there must be some endeavour or motion in the sucking to attract the [Page] sucked Body. But in our last Experiment it appears not at all how the upper part of the empty'd Cylinder that remains moveless all the while, or any part of it, doth at all endeavour to draw to it the depressed Sucker and the annexed weights. And yet those that behold the ascension of the Sucker, without seriously considering the cause of it, do readily conclude it to be raised by something that powerfully Sucks or attracts it, though they see not what that may be or where it lurks. So that it seems not absolutely necessary to Suction, that there be in the Body, which is said to suck, an endeavour or motion in order thereunto, but rather that Suction may be at least for the most part reduced to Pulsion, and its effects ascrib'd to such a pressure of the neighbouring Air upon those Bodies (whether Aërial, or of other natures) that are contiguous to the Body that is said to attract them, as is stronger, than that substance, which possesseth the cavity of that sucking Body, is able to resist. To object here, that it was some particles of Air remaining in the emptied Cylinder that attracted this weight to obviate a Vacuum, will scarce be satisfactory; unless it can be clearly made out by what little hooks, or other grappling Instruments, the internal Air could take hold of the Sucker; how so little of it obtained the force to lift up so great a weight; and why also, upon the letting in of a little more Air into one of our evacuated Vessels, the attraction is, instead of being strengthened, much weakned; though, if there were danger of a Vacuum before, it would remain, notwithstanding this ingress of a little Air. For that still there remained in the capacity of the exhausted Cylinder store of little rooms, or spaces empty or devoid of Air, may appear by the great violence wherewith the Air rusheth in, if any way be open'd to it. And that 'tis not so much the decrement of the Vacuum within the cavity of the vessel that debilitates the attraction, as the Spring of the included Air (whose presence makes the decrement) that doth it by resisting the pressure of the external Air, seems probable, partly from the Disability of vacuities, whether greater or lesser, to resist the pressure of the Air; and partly by some of the Phaenomena of our Experiments, and particularly [Page] by this Circumstance of the Three and Thirtieth, that the Sucker was, by the pressure of the Ambient Air, impell'd upwards with its weight hanging at it, not onely when it was in the bottom of the Cylinder, and consequently left a great Vacuum in the cavity of it; but when the Sucker had been already impell'd almost to the top of the Cylinder, and consequently, when the Vacuum that remain'd was become very little in comparison of that which preceded the beginning of the Sucker's ascension.

In the next place, these Experiments may teach us, what to judge of the vulgar Axiom received for so many Ages as an undoubted Truth in the Peripatetick Schools; That Nature abhors and flyeth a Vacuum, and that to such a degree, that no humane power (to go no higher) is able to make one in the Universe; wherein Heaven and Earth would change places, and all its other Bodies rather act contrary to their own Nature, than suffer it. For, if by a Vacuum we will understand a place perfectly devoid of all corporeal Substance, it may indeed then, as we formerly noted, be plausibly enough maintained that there is no such thing in the world; but that the generality of the Plenists, (especially till of late years some of them grew more wary) did not take a Vacuum in so strict a sense, may appear by the Experiments formerly, and ev'n to this day imploy'd by the Deniers of a Vacuum, to prove it impossible that there can be any made. For when they alledge (for Instance) that when a man sucks Water through a long Pipe, that heavy Liquor, contrary to its Nature, ascends into the Sucker's mouth, only, to fill up that room made by the Dilatation of his Breast and Lungs, which otherwise will in part be empty. And when they tell us, that the reason why if a long Pipe exactly clos'd at one end be filled top-full of Water, and then inverted, no Liquor will fall out of the open Orifice; Or, to use a more samiliar Example, when they teach, that the cause, why in a Gardiner's watering Pot shaped conically, or like a Sugar-Loaf, fill'd with Water, no Liquor falls down through the numerous holes at the bottom, whilst the Gardiner keeps his Thumb upon the [Page] Orifice of the little hole at the top, and no longer; must be that if in the case proposed the Water should descend, the Air being unable to succeed it, there would be le [...]t at the upper and deserted part of the Vessel a Vacuum, that would be avoided if the hole at the top were open'd. When (I say) they alledge such Experiments, the tendency of them seems plainly to import, that they mean, by a Vacuum, any space here below that is not filled with a visible body, or at least with Air though it be not quite devoy'd of all Body whatsoever. For why should Nature, out of her detestation of a Vacuum, make Bodies act contrary to their own tendency, that a place may be fill'd with Air, if its being so were not necessary to the avoiding of a Vacuum.

Taking then a Vacuum in this vulgar and obvious sense, the common opinion about it seems lyable to several Exceptions, whereof some of the chief are suggested to us by our Engine.

It will not easily then be intelligibly made out, how hatred or aversation, which is a passion of the Soul, can either for a Vacuum, or any other object, be supposed to be in Water, or such like inanimate Body, which cannot be presumed to know when a Vacuum would ensue; if they did not bestir themselves to prevent it: nor to be so generous as to act contrary to what is most conducive to their own particular preservation for the publique good of the Universe. As much then of intelligible and probable Truth, as is contain'd in this Metaphorical Expression, seems to amount but to this; That by the Wise Authour of Nature (who is justly said to have made all things in number, weight and measure,) the Universe, and the parts of it, are so contriv'd, that it is as hard to make a Vacuum in it, as if they studiously conspir'd to prevent it. And how far this it self may be granted, deserves to be farther consider'd.

For in the next place, our Experiments seem to teach, that the supposed Aversation of Nature to a Vacuum is but accidental, or in consequence, partly of the Weight and Fluidity, or, at least, Fluxility of the Bodies here below; and partly, and perhaps [Page] principally, of the spring of the Air, whose restless endeavour to expand it self every way, makes it either rush in it self, or compel the interposed Bodies into all spaces, where it finds no greater resistance than it can surmount. And that in those motions which are made ob fugam Vacui (as the common phrase is) Bodies act without such generosity and consideration, as is wont to be ascrib'd to them, is apparent enough in our 32d Experiment, where the torrent of Air, that seem'd to strive to get into the empty'd Receiver, did plainly prevent its own design by so impelling the Valve, as to make it shut the only Orifice the Air was to get out at. And if afterwards either Nature, or the internal Air, had a design the external Air should be attracted, they seem'd to prosecute very unwisely by continuing to suck the Valve so strongly; when they found that by that Suction the Valve it self could not be drawn in: Whereas by forbearing to suck, the Valve would by its own weight have fallen down, and suffer'd the excluded Air to return freely, and to fill again the exhausted Vessel.

And this minds me to take notice of another deficiency, pointed at by our Experiments in the common Doctrine of those Plenists we reason with; for many of those unusual motions in Bodies, that are said to be made to escape a Vacuum, seem rather made to fill it. For why, to instance in our newly mention'd Experiment, as soon as the Valve was depressed by the weight we hung at it, should the Air so impetuously and copiously rush into the cavity of the Receiver; if there were before no vacant room there to receive it? and if there were, then all the while the Valve kept out the Air, those little spaces in the Receiver, which the corpuscles of that Air afterwards fill'd, may be concluded to have remain'd empty. So that the seeming violence, imploy'd by Nature on the occasion of the evacuating of the Vessel, seems to have come too late to hinder the making of Vacuities in the Receiver, and only to have, as soon as we permitted, fill'd up with Air those that were already made.

And as for the care of the publique good of the Universe ascrib'd to dead and stupid Bodies, we shall only demand, why [Page] in our 19th Experiment, upon the Exsuction of the ambient Air, the Water deserted the upper half of the Glass-Tube; and did not ascend to fill it up, till the external Air was let in upon it: whereas by its easie and sudden regaining that upper part of the Tube, it appeared both that there was there much space devoid of Air, and that the Water might with small or no resistance have ascended into it, if it could have done so without the impulsion of the re-admitted Air; which, it seems, was necessary to mind the Water of its formerly neglected Duty to the Universe.

Nay, for ought appeareth, even when the excluded Air, as soon as 'twas permitted, rush'd violently into our exhausted Receiver, that flowing in of the Air proceeded rather from the determinate Force of the Spring of the neighbouring Air, than from any endeavour to fill up, much less to prevent vacuity's. For though when as much Air as will, is gotten into our Receiver our present Opponents take it for granted that it is full of Air; yet if it be remembred that when we made our 17th Experiment we crouded in more Air to our Receiver than it usually holds; and if we also consider (which is much more) that the Air of the same consistence with that in our Receiver may in Wind-guns, as is known, and as we have tryed, be compressed at least into half its wonted room (I say at least, because some affirm, that the Air may be thrust into an 8th, or a yet smaller part of its ordinary extent) it seems necessary to admit either a notion of condensation and rarefaction that is not intelligible, or that in the capacity of our Receiver when presumed to be full of Air, there yet remain'd as much of space as was taken up by all the Aërial corpuscles, unpossessed by the Air. Which seems plainly, to infer that the Air that rush'd into our empty'd vessel did not doe it precisely to fill up the Vacuities of it, since it left so many unfill'd, but rather was thrust in by the pressure of the contiguous Air: which as it could not, but be always ready to expand it self, where it found least resistance, so was it unable to fill the Receiver any more, than untill the Air within was reduc'd to the same measure of Compactness with that without.

[Page]We may also from our two already often mention'd Experiments farther deduce, that, (since Natures hatred of a Vacuum is but Metaphorical and Accidental, being but a consequence or result of the pressure of the Air and of the Gravity, and partly also of the Fluxility of some other Bodies) The power she makes use of to hinder a Vacuum, is not (as we have else-where also noted) any such boundless thing as men have been pleased to imagine. And the reasons why in the former Experiments, mentioned in favour of the Plenists, Bodies seem to forget their own Natures to shun a Vacuum, seems to be but this; That in the alledged cases the weight of that Water that was either kept from falling or impell'd up, was not great enough to surmount the pressure of the contiguous Air; which, if it had been, the Water would have subsided, though no Air could have succeeded. For not to repeat that Experiment of Monsieur Paschal (formerly mention'd to have been tryed in a Glass exceeding 32. Foot) wherein the inverted Pipe being long enough to contain a competent-weight of Water, that Liquor freely ran out at the lower Orifice: Not to mention this (I say) we saw in our nineteenth Experiment, that when the pressure of the ambient Air was sufficiently weakn'd, the Water would fall out apace at the Orifice even of a short Pipe, though the Air could not succeed into the room deserted by it. And it were not amiss if tryal were made on the tops of very high Mountains, to discover with what case a Vacuum could be made near the confines of the Atmosphere, where the Air is probably but light in comparison of what it is here below. But our present (three and thirtieth) Experiment seems to manifest, not onely that the power, exercis'd by Nature, to shun or replenish a Vacuum, is limitted, but that it may be determin'd even to Pounds and Ounces: Insomuch that we might say, such a weight Nature will sustain or will lift up to resist a Vacuum in our Engine; but if an Ounce more be added to that weight, it will surmount Her so much magnifi'd detestation of Vacuities. And thus, My Lord, our Experiments may not onely answer those of the Plenists, but enable us to retort their Arguments against themselves: since, if that be true which [Page] they alleadge, that, when Water falls not down according to its nature, in a Body wherein no Air can succeed to fill up the place it must leave, the suspension of the Liquor is made Ne detur Vacuum, (as they speak) it will follow, that if the Water can be brought to subside in such a case, that deserted space may be deem'd empty, according to their own Doctrine; especially, since Nature (as they would perswade us) bestirs her self so mightily to keep it from being deserted.

I hope I shall not need to remind Your Lordship, that I have all this while been speaking of a Vacuum, not in the strict and Philosophical sense, but in that more obvious and familiar one that hath been formerly declar'd.

And therefore I shall now proceed to observe in the last place, that our 33d Experiment affords us a notable proof of the unheeded strength of that pressure which is sustain'd by the Corpuscles of what we call the free Air, and presume to be uncompressed. For, as fluid and yielding a Body as it is, our Experiment teacheth us, That ev'n in our Climate, and without any other compression than what is (at least here below) Natural, or (to speak more properly) ordinary to it, it bears so strongly upon the Bodies whereunto it is contiguous, that a Cylinder of this free Air, not exceeding three Inches in Diameter is able to raise and carry up a weight, amounting to between sixteen and seventeen hundred Ounces. I said even in our Climate, because that is temperate enough; Aere frigido existente tardius moventar Automata quam aere calido, adeo quidem at Automaton quod Belgae in Nova Zembla agentes in aedibus suis collocaverunt omnino à motu cessaverit etsimulto majus pondus ei addidissent quam antea serre solebat. Varenius Geo: General. lib. 111. Propo: 7. pag. 648. and as far as my observations assist me to conjecture, the Air in many other more Northern Countries may be much thicker, and able to support a greater weight: which is not to be doubted of, if there be no mistake in what is Recorded concerning the Hollanders, that were forc'd by the Ice to Winter in Nova Zembla, namely, That they found there so condens'd an Air, that they could not make their Clock goe, ev'n by a very great addition to the weights that were wont to move it.

[Page]I suppose Your Lordship will readily take notice, that I might very easily have discoursed much more fully and accurately than I have done, against the common opinion touching Suction, and touching natures hatred of a Vacuum. But I was willing to keep my self to those considerations touching these matters, that might be verified by our engine it self, especially, since, as I said at first, it would take up too much time to insist particularly upon all the Reflexions that may be made even upon our two last Experiments. And therefore passing to the next, I shall leave it to Your Lordship to consider how far these tryals of ours will either confirm or disfavour the new Doctrine of several eminent Naturalists, who teach, That in all motion there is necessarily a Circle of Bodies, as they speak, moving together; and whether the Circles in such motion be an Accidental or Consequential thing or no.

EXPERIMENT XXXIIII.

'TIs a known thing to those that are conversant in the Hydrostaticks, That two Bodies which in the Air are of equal weight, but of unequal bulk, as Gold, for instance and Iron, being afterwards weighed in Water, will lose their AEquilibrium upon the change of the ambient Body: so that the Gold will sink lower than the Iron; which, by reason of its greater bulk, hath more Water to lift or displace, that it may sink. By Analogy to this Experiment, it seemed probable, that if two weights did in our Engine ballance each other, when the Glass was full of Air; upon the exsuction of a great part of that Air, so notable a change in the consistence of the ambient Body, would make them lose their AEquilibrium.

But being desirous at the same time to make a tryal, for a certain Design that needs not here be mention'd, we took for one of our weights a dry Bladder, strongly tyed at the Neck, and about half fill'd with Air (that being a weight both slight, and that would expand it self in the evacuated Glass) and fastning that to one part of our formerly mentioned exact ballance (which turns with the 32d part of a Grain) we put a Metalline [Page] counterpoise into the opposite Scale; and so the two weights being brought to an AEquilibrium, the ballance was convey'd into the Receiver, and suspended from the Cover of it.

But before we proceed farther, we must note, That presently after the laying on of the Cover, the Bladder appear'd to preponderate, whereupon the Scales being taken out, and reduc'd very near to an AEquilibrium, yet so, that a litle advantage remained on that side to which the Metalline weight belonged; they were again let down into the Receiver, which was presently made fast with Plaister, and a hot Iron: Soon after which before the Pump was employ'd, the Bladder seem'd again a little to preponderate. Afterwards the Air in the Glass being begun to be drawn out, the Bladder began (according to the formerly mention'd Observations) to expand it self, and manifestly to outweigh the opposite weight, drawing down the Scale to which it was fastned very much beneath the other, especially when the Air had swell'd it to its full extent.

This done, we very leisurely let in the external Air; and observ'd, that upon the flagging of the Bladder, the Scale whereto it was fastned, not onely by degrees return'd to an AEquilibrium with the other, but at length was a little outweighed by it.

But because we suspected there might have interven'd some unheeded Circumstance in this last part of the Experiment we would not presently take out the Scales, nor meddle with the Cover, but leaving things as they were, we perceiv'd, that after a little while the Bladder began again to preponderate, and by degrees to sink lower and lower for divers hours, wherefore, leaving the Vessel closed up all night, we repair'd to it next Morning, and found the Bladder fallen yet lower. As if the very substance of it, had imbibed some of the moisture wherewith the Air (the Season being very rainy) did then abound: As Lutestrings, which are made likewise of the Membranous parts of Guts, strongly wreath'd, are known to swell so much oftentimes as to break in rainy and wet weather. Which conjecture is the more to be regarded, because congruously unto it one of the company having a little warm'd the Bladder, found [Page] it then lighter than the opposite weight. But this must be look'd upon as a bare conjecture, till we can gain time to make farther tryals about it. In the mean while we shall adde, that without removing the Scales or the Cover of the Receiver, we again caused the Air to be drawn out (the weather continuing very moist) but found not any manifest alteration in the ballance; whether because the AEquilibrium was too far lost to let a small change appear, we determine not.

But to make the Experiment with a Body less apt to be altered by the temperature of the Air, than was the Bladder; we brought the Scales again to an AEquilibrium with two weights, whereof the one was of Lead, the other of Cork. And having evacuated the Receiver, we observed, that both upon the exsuction, and after the return of the Air, the Cork did manifestly preponderate, and much more, a while after the Air had been let in again, than whilst it was kept out. Wherefore, in the room of the Cork, we substituted a piece of Char-coal, as less likely to imbibe any moisture from the Air, but the event proved much the same with that newly related: So that this Experiment seems more liable to Casualties than any, excepting one we have made in our Engine. And as it is difficult to prevent them, so it seems not very easie to discover the causes of them, whereof we shall therefore at present forbear mentioning our Conjectures.

EXPERIMENT XXXV.

SOme Learned Mathematicians have of late ingeniously endeavoured to reduce Filtres to Siphons; but still the true cause of the ascension of Water, and other Liquors both in Siphons and in Filtration, needing (for ought we have yet found) a clearer Discovery and Explication, we were desirous to try whether or no the pressure of the Air might reasonably be supposed to have either the principal, or at least a considerable Interest in the raising of those Liquors. But because we found that we could not yet so evacuate our Receiver, but that the remaining Air though but little in comparison of the exhausted, would be able to impell the Water to a greater height than is usual in ordinary Filtrations: [Page] we resolved instead of a List of Cotton, or the like Filtre, to make use of a Siphon of Glass, delineated in the third Figure, consisting of three pieces, two streight, and the third crooked to joyn them together; whose Junctures were diligently clos'd that no Air might find entrance at them. One of the Legs of this Siphon was (as it should be) somewhat longer than the other, and was pervious at the bottom of it onely, by a hole almost as slender as a hair, that the Water might but very leasurely drop out of it, lest it should all run out before the Experiment were compleated. The other and shorter Leg of the Siphon was quite open at the end, and the same wideness with the rest of the Pipe, whose bore was about ¼ of an Inch. The whole Siphon made up of these several pieces put together, was design'd to be about a Foot and a half long; that the remaining Air, when the Vessel was exhausted after the wonted manner, might not be able to impell the Water to the top of the Siphon; which being inverted, was fill'd with Water, and of which the Shorter leg being let down two or three Inches deep into a Glass Vessel full of Water, and the upper parts of it being fasten'd to the inside of the Cover of the Receiver, we proceeded to close first, and then to empty the Vessel.

The effect of the tryal was this, That till a pretty quantity of Air had been drawn out, the Water dropp'd freely out at the lower end of the lower leg of the Siphon, as if the Experiment had been performed in the free Air. But afterwards, the Bubbles (as had been apprehended) began to disclose themselves in the Water, and ascending to the top of the Siphon, imbodyed themselves there into one, which was augmented by little and little, by the rising of other bubbles that from time to time broke into it, but much more by its own dilatation, which increas'd proportionably to the exsuction that was made of the Air out of the Receiver. So that at length the Water in the shorter Leg of the Siphon was reduc'd, partly by the extraction of the ambient Air, and partly by the expansion of the great Bubble at the upper part of the Siphon, to be but about a Foot high, if so much; whereby it came to pass, that the course of the Water [Page] in the Siphon was interrupted, and that which remain'd in the longer Leg of it, continu'd suspended there without dropping any longer. But upon the turning of the Stop-cock, the outward Air (being let into the Receiver) got into the Siphon, by the little hole at which the Water formerly dropt out; and traversing all the incumbent Cylinder of Water, in the form of Bubbles, joynd it self with that Air that before possess'd the top of the Siphon.

To prevent the inconveniences arising from these Bubbles, two Glass Pipes, like the former, were so placed, as to terminate together in the midst of the Belly of a Glass Viol, into whose Neck they were carefully fasten'd with Cement; and then both the Viol and the Pipes being (which was not done without difficulty) totally fill'd with Water, the Siphon describ'd in the fifth Figure, was plac'd with its shorter Leg in the Glass of Water as formerly; and the Experiment being prosecuted after the same manner, much more Air than formerly was drawn out, before the bubbles, disclosing themselves in the water, were able to disturb the Experiment; because that in the capacity of the Viol there was room enough for them to stretch themselves, without depressing the Water below the ends of the Pipes; and during this time, the Water continued to drop out of the propending Leg of the Siphon. But at length the Receiver being very much empty'd, the passage of the Water through the Siphon ceas'd, the upper ends of the Pipes beginning to appear a little above theremaining Water in the Viol, whose dilated Air appear'd likewise to press down the Water in the Pipes, and fill the upper part of them.

And hereby the continuity of the Water, and so the Experiment it self being interrupted we were invited to let in the Air again, which, according to its various proportions of pressure to that of the Air in the Viol and the Pipes, did for a good while exhibite a pleasing variety of Phaenomena, which we have not now the leasure to recite. And though upon the whole matter there seem'd little or no cause to doubt, but that, if the Bubbles had not disturb'd the Experiment, it would manifestly enough have appear'd that the course of Water through Siphons depends [Page] upon the pressure of the Air: yet we resolv'd, at our next leasure and conveniency, to try the Experiment again, with a quantity of Water before freed from Bubbles by the help of the same Engine.

This occasion I have had to take notice of Siphons, puts me in mind of an odde kind of Siphon that I caus'd to be made ā pretty while ago; and which hath been since, by an Ingenious Man of Your acquaintance, communicated to divers others. The occasion was this: An eminent Mathematician told me one day, that some inquisitive French Men (whose Names I know not) had observ'd, That in case one end of a slender and perforated Pipe of Glass be dip'd in Water, the liquor will ascend to some height in the Pipe, though held perpendicular to the plain of the Water. And, to satisfie me that he mis-related not the Experiment, he soon after brought two or three small Pipes of Glass, which gave me the opportunity of trying it: though I had the less reason to distrust it, because I remember I had often, in the long and slender Pipes of some weather Glasses, which I had caus'd to be made after a somewhat peculiar fashion, taken notice of the like ascension of the Liquor, though (presuming it might be casual) I had made but little reflexion upon it. But after this tryal, beginning to suppose, that though the Water in these Pipes that were brought me, rise not above a quarter of an Inch, (if near so high) yet, if the Pipes were made slender enough, the Water might rise to a very much greater height; I caus'd several of them to be, by a dexterous Hand, drawn out at the flame of a Lamp, in one of which that was almost incredibly slender we found that the Water ascended (as it were of it self) five Inches by measure, to the no small wonder of some famous Mathematicians, who were Spectators of some of these Experiments. And this height the Water reach'd to, though the Pipe were held in as erected a posture as we could: For if it were inclin'd, the Water would fill a greater part of it, though not rise higher in it. And we also found, that when the inside of the Pipe was wetted beforehand, the Water would rise much better than otherways: But we caus'd not all our slender Pipes to be [Page] made streight, but some of them crooked, like Siphons: And having immers'd the shorter Leg of one of these into a Glass that held some fair Water, we found, as we expected, that the Water arising to the top of the Siphon, though that were high enough, did of it self run down the longer Leg, and continue running like an ordinary Siphon. The cause of this ascension of the Water, appear'd to all that were present so difficult, that I must not stay to enumerate the various Conjectures that were made at it, much less to examine them; especially having nothing but bare Conjectures to substitute in the room of those I do not approve. We try'd indeed, by conveying a very slender Pipe and a small Vessel of Water into our Engine, whether or no the exsuction of the ambient Air would assist us to find the cause of the ascension we have been speaking of: But though we imploy'd red Wine instead of Water, yet we could scarce certainly perceive thorow so much Glass, as was interpos'd betwixt our eyes and the Liquor, what happen'd in a Pipe so slender that the redness of the Wine was scarce sensible in it. But as far as we could discern, there happen'd no great alteration to the Liquor: which seem'd the less strange, because the spring of that Air that might depress the Water in the Pipe, was equally debilitated with that which remain'd to press upon the surface of the Water in the little Glass. Wherefore, in favor of his Ingenious Conjecture who ascrib'd the Phaenomenon under consideration, to the greater pressure made upon the water by the Air without the Pipe, than by that within it, (where so much of the Water (consisting perhaps of Corpuscles more pliant to the internal surfaces of the Air) was contiguous to the Glass) it was shown, that in case the little Glass Vessel that held the water, of which a part ascended into the slender Pipe, were so clos'd, that a Man might with his mouth suck the Air out of it, the water would immediately subside in the small Pipe. And this would indeed infer, that it ascended before onely by the pressure of the incumbent Air; But that it may (how justly I know not) be objected, That peradventure this would not happen, in case the upper end of the Pipe were in a Vacuum: And that 'tis very probable the [Page] water may subside, not because the pressure of the internal Air is taken off by Exsuction, but by reason of the spring of the external Air, which impels the Water it findes in its way to the cavity deserted by the other Air, and would as well impel the same water upwards, as make it subside, if it were not for the accidental posture of the Glasses. However, having not now leisure to examine any farther this Matter, I shall onely mind Your Lordship, that if You will prosecute this Speculation, it will be pertinent to find out likewise, Why the surface of water (as is manifest in Pipes) useth to be concave, being depress'd in the middle, and higher on every side? and why in Quicksilver on the contrary, not onely the surface is wont to be very convex, or swelling, in the middle; but if you dip the end of a slender Pipe in it, the surface of the Liquor (as 'tis call'd) will be lower within the Pipe, than without. Which Phaenomena, whether, and how far, they may be deduc'd from the Figure of the mercurial Corpuscles, and the Shape of the springy Particles of the Air, I willingly leave to be consider'd.

EXPERIMENT XXXVI.

SEveral ways we have met with propos'd, partly by the excellent Galileo, and partly by other ingenious Writers, to manifest that the Air is not devoid of weight; some of these require the previous absence of the Air to be weighed; and others, the violent condensation of it. But if we could list a pair of Scales above the Atmosphere, or place them in a Vacuum, we might there weigh a parcel of Air it self, as here we do other Bodies in the Air, because it would there be heavier than that which surrounds it, as are grosser Bodies we commonly weigh, than the medium or ambient Air. Wherefore, though we have above declin'd to affirm, that our Receiver, when emptyed, deserves the name of a true Vacuum, and though we cannot yet perfectly free it from Air it self, yet we thought fit to try how far the Air would manifest its gravity in so thin a medium, as we could make in our. Receiver, by evacuating it. We caus'd then to be blown at the Flame of a Lamp, a Glass bubble of [Page] about the bigness of a small Hen-egge, and of an Oval form, save that at one end there was drawn out an exceeding slender Pipe, that the Bubble might be sealed up, with as little rarefaction as might be, of the Air included in the great or Oval Cavity of it. This Glass being sealed, was fastened to one of the Scales of the exact pair of Ballances formerly mention'd; and being counterpois'd with a weight of Lead, was convey'd into the Receiver, and clos'd up in it. The Beam appearing to continue Horizontal, the Pump was set on work, and there scarce past above two or three Exsuctions of the Air, before the Ballance lost its Equilibrium, and began to incline to that side on which the Bubble was; which, as the Air was farther and farther drawn out, did manifestly more and more preponderate, till he that pumped began to grow weary of his Imployment: after which the Air being leisurely let in againe, the Scales by degrees returned to their former Equilibrium. After that we took them out, and casting into that Scale to which the lead belonged three quarters of a grain, we conveyed the ballance into the Receiver, which being closed up, and exhausted as before, we observ'd, that as the Air was drawn out more and more, so the Glass bubble came nearer and nearer to an Equilibrium with the other weight, till at length the Beam was drawn to hang Horizontal; which (as we had found by another tryal) we could not bring it to do, when a quarter of a Grain more was added to the Scale, to which the Lead belong'd: though it seem'd questionless, that if we could have perfectly empty'd the Receiver of the contain'd Air, that included in the bubble would have weighed above a Grain, notwithstanding its having been probably somewhat rarefied by the flame, by the help of which, the bubble was seal'd up. Let us adde, That on the regress of the excluded Air, the Lead, and the weight cast into the same scale, did again very much preponderate.

We likwise convey'd into the Receiver, the same bubble, open'd at the end of the slender Pipe above-mention'd, but having drawn out the Air, after the accustomed manner, we found not as before, the bubble to out-weigh the opposite Lead: so [Page] that by the help of our Engine we can weigh the Air, as we weigh other Bodies, in its natural or ordinary consistence, without at all condensing it: Nay, which is remarkable, having convey'd a Lambs bladder about half full of Air into the Receiver, we observed, that though upon the drawing out of the ambient Air, the imprisoned Air so expanded it self, as to distend the Bladder so, as to seem ready to Break it; yet this rarefied Air did manifestly depress the Scale whereunto it was annexed.

Another thing we must not forget to mention, that happened to us, whilst we were making tryals concerning the weight of the Air; namely, that having once caus'd the Pump to be somewhat obstinately ply'd, to discover the better what may be expected from the thinness of the medium in this Experiment; the Imprison'd Air broke its brittle Prison, and throwing the greatest part of it against the side of the Receiver, dash'd it against that thick Glass into a multitude of pieces. Which accident I mention, partly that it may confirm what we deliver'd in our Reflexions, upon the first Experiment, where we considered what would probably be done by the spring of the Air Imprison'd in such Glasses, in case the ballancing pressure of the ambient Air were withdrawn; and partly, that we may thence discern of how close a Texture Glass is, since so very thin a film of Glass (if I may so call it) prov'd so impervious to the Air, that it could not get away through the Pores, but was forc'd to break the Glass in pieces to free it self; and this, notwithstanding the time and advantage it had to try to get out at the Pores. And this I mention, that neither our Experiments, nor those of divers Learned Men, might receive any prejudice from an Experiment which I happen'd to make divers years ago, and which, having been so much taken notice of by curious Men, may be drawn to countenance their erroneous Opinion, who would fain perswade us, That Glass is penetrable by Air properly so called. Our Experiment was briefly this: We were distilling a certain Substance, that much abounded with subtle Spirits and volatile Salt, in a strong Earthen vessel of an unusual shape, to which was luted a large Receiver, made of the course sort of Glass (which the [Page] Trades-men are wont to call green Glass) but in our absence, the Fire, though it were to be very strong, was, by the negligence or mistake of those we appointed to attend it, so excessively increas'd, that when we came back to the Fornace, we found the spirituous and saline Corpuscles pour'd out (if I may so call it) so hot, and so copiously into the Receiver, that they made it all opacous, and more likely to flie in pieces, than fit to be touch'd. Yet, being curious to observe the effects of a Distillation, prosecuted with so intense and unusual a degree of heat, we ventur'd to come near, and observ'd, among other things, that on the outside of the Receiver, at a great distance from the juncture, there was setled a round whitish Spot or two, which at first we thought might be some stain upon the Glass; but after, finding it to be in divers Qualities like the Oyl and Salt of the Concrete we were Distilling, we began to suspect that the most subtle and fugitive parts of the impetuously ascending Steams, had penetrated the substance (as they speak) of the Glass, and by the cold of the ambient Air were condensed on the surface of it. And though we were very backward to credit this suspition, and therefore call'd in an Ingenious Person or two, both to assist us in the Observation, and have Witness of its event, we continued a while longer to watch the escape of such unctuous Fumes; and upon the whole matter unanimously concluded that (all things consider'd) the subtle parts of the distill'd matter being violently agitated, by the excessive heat that pass'd through the Pores of the Glass, widn'd by the same heat. But this having never happen'd but once in any of the Distillations we have either made or seen, though these be not a few, it is much more reasonable to suppose, that the perviousness of our Receiver to a Body much more subtle than Air, proceeded partly from the looser Texture of that particular parcel of Glass the Receiver was made of (for Experience hath taught us, that all Glass is not of the same compactness and solidity) and partly from the enormous heat, which, together with the vehement agitation of the penetrant Spirits, open'd the Pores of the Glass; than to imagine that such a substance as Air, should be able to permeate the Body [Page] of Glass contrary to the testimony of a thousand Chymical and Mechanical Experiments, and of many of those made in our Engine, especially that newly recited: Nay, by our fifth Experiment it appears that a thin Bladder will not at its Pores give passage even to rarefied Air. And on this occasion we will annex an Experiment, which hath made some of those we have acquainted with it, doubt, whether the Corpuscles of the Air be not less subtle than those of Water.

But without examining here the reasonableness of that doubt, we will proceed to recite the Experiment it self, which seems to teach, That though Air, when sufficiently compressed, may perchance get entrance into narrower holes and crannies than Water; yet unless the Air be forc'd in at such very little holes, it will not get in at them, though they may be big enough to let Water pass through them.

The Experiment then was this: I took a fair Glass Siphon, the lower end of whose longest Leg was drawn by degrees to such a slenderness, that the Orifice, at which the Water was to fall out, would hardly admit a very small Pin: This Siphon being inverted, the matter was so order'd, that a little Bubble of Air was intercepted in the slenderest part of the Siphon, betwixt the little hole newly mention'd, and the incumbent Water, upon which it came to pass, that the Air being not to be forc'd through so narrow a passage, by so light a Cylinder of Water, (though amounting to the length of divers Inches,) as lean'd upon it, hindered the farther efflux of the Water, as long as I pleased to let it stay in that narrow place: whereas, when by blowing a little at the wider end of the Siphon, that little parcel of Air was forced out with some Water, the remaining Water, that before continu'd suspended, began freely to drop down again as formerly. And if you take a Glass Pipe, whether it be in the form of a Siphon, or no, that being for the most part of the thickness of a Mans Finger, is yet towards one end so slender, as to terminate in a hole almost as small as a Horse-hair; and if you fill this Pipe with Water, you will find that Liquor to drop down freely enough thorow the slender Extream: But if you then invert [Page] the Pipe, you will find that the Air will not easily get in at the same hole through which the Water passed. For in the sharp end of the Pipe, some Inches of water will remain suspended, which, 'tis probable, would not happen, if the Air could get in to succeed it, since if the hole were a little wider, the Water would immediately subside. And though it be true, that if the Pipe be of the length of many Inches, a great part of the Water will run down at the wider Orifice: yet that seems to happen for some other reason, than because the Air succeeds it at the upper and narrow Orifice, since all the slender part of the Pipe, and perhaps some Inches more, will continue full of Water.

And on this occasion I remember, that whereas it appears by our fifth Experiment, That the Aërial Corpuscles (except perhaps some that are extraordinarily fine) will not pass thorow the Pores of a Lambs Bladder, yet Particles of Water will, as we have long since observ'd, and as may be easily try'd, by very closely tying a little Alcalizate Salt (we us'd the Calx of Tartar made with Nitre) in a fine Bladder, and dipping the lower end of the Bladder in Water; for if you hold it there for a competent while, you will find that there will strain thorow the Pores of the Bladder, Water enough to dissolve the Salt into a Liquor.

But I see I am slip'd into a Digression, wherefore I will not examine, whether, the Experiment I have related, proceeded from hence, That the springy Texture of the Corpuscles of the Air, makes them less apt to yield and accommodate themselves easily to the narrow Pores of Bodies, than the more flexible Particles of Water; or whether it may more probably be ascrib'd to some other Cause. Nor will I stay to consider how far we may hence be assisted to ghess at the cause of the ascension of Water in the slender Pipes, and Siphons formerly mention'd, but will return to our Bubble; and take notice, That we thought fit also to endeavor to measure the capacity of the Bubble we had made use of, by filling it with Water, that we might the better know how much Water answer'd in weight to ¾ of a Grain of Air, but notwithstanding all the diligence that was used to preserve so brittle a Vessel, it broke before we could perfect [Page] that we were about, and we were not then provided of another Bubble fit for our turn.

The haste I was in, My Lord, when I sent away the last Sheet, made me forget to take notice to you of a Problem that occurr'd to my thoughts, upon the occasion of the slow breaking of the Glass Bubble in our evacuated Receiver. For it may seem strange, since by our sixth Experiment it appears, that the Air, when permitted, will by its own internal Spring expand it self twice as much as Mersennus was able to expand it, by the heat even of a candent AEolipile: Yet the Elater of the Air was scarce able to break a very thin Glass Bubble, and utterly unable to break one somewhat thicker, within whose cavity it was imprison'd; whereas Air pen'd up and agitated by heat is able to perform so much more considerable effects, that (not to mention those of Rarefaction that are more obvious) the Learned Jesuit Cabaeus (he that writ of the Load-stone) relates, That he saw a Marble Pillar (so vast, that three men together P: Nicol: Cab: lib: 4. Meteor: Aristot: with display'd arms could not imbrace it, and that 1000 Yoke of Oxen drawing it several ways with all their strength, could not have torn it assunder) quite broken off in the midst, by reason of some Wood, which happening to be burnt just by the Pillar the heat proceeding from the neighbouring Fir, so rarefied some Air or Spirituous Matter which was shut up in the cavities of the Marble, that it broke through the solid Body of the Stone to obtain room to expand it self.

I remember I have taken notice that probably the reason why the included Air did not break the hermetically seal'd Bubbles that remain'd intire in our emptyed Receiver, was, That the Air, being somewhat rarefied by the flame imploy'd to close the Glass, its Spring, upon the recess of the heat, grew weaker than before. But though we reject not that ghess, yet it will not in the present case serve the turn, because that much smaller Glass bubbles exactly clos'd, will, by the included Air (though agitated by the heat of a very moderate Fire) be made to fly in pieces. Whether we may be assisted to salve this Problem, by considering that the heat doth from within vehemently agitate the Corpuscles [Page] of the Air, and add its assistance to the Spring they had before, I shall not now examine: since I here but propose a Problem, and that chiefly that by this memorable Story of Cabaeus, notice may be taken of the prodigious power of Rarefaction, which hereby appears capable of performing stranger things than any of our Experiments have hitherto ascrib'd to it.

We should hence, My Lord, immediately proceed to the next Experiment, but that we think it fit, on this occasion, to acquaint You with what some former tryals (though not made in our Engine) have taught us, concerning what we would have discover'd by the newly mention'd Bubble that broke. And this the rather, because (a great part of this Letter supposing the gravity of the Air) it will not be impertinent to determine more particularly than hitherto we have done, what gravity we ascribe to it.

We took then an AEolipile made of Copper, weighing six ounces, five drachms, and eight and forty grains: this being made as hot as we durst make it, (for fear of melting the mettle, or at least the Sodar) was removed from the fire and immediately stopped with hard Wax that no Air at all might get in at the little hole, wont to be left in AEolipiles for the fumes to issue out at: Then the AEolipile being suffer'd leasurely to cool, was again weighed together with the Wax that stopt it, and was found to weigh (by reason of the additional weight of the Wax) six ounces, six drachms, and 39 grains. Lastly, the Wax being perforated without taking any of it out of the Scale, the external Air was suffered to rush in (which it did with some noise) and then the AEolipile and Wax, being again weighed amounted to six ounces, six drachms, and 50 grains. So that the AEolipile freed as far as our fire could free it, from its Air, weighed less than it self when replenished with Air, full eleven grains. That is, the Air containable within the cavity of the AEolipile amounted to eleven grains and somewhat more; I say somewhat more, because of the particles of Air, that were not driven by the fire out of the AEolipile. And by the Way (if there be no mistake in the observations of the diligent Mersennus) it may seem strange [Page] that it should so much differ from 2 or 3 of ours; in none of which we could rarefie the Air in our AEolipile (though made red hot almost all over, and so immediately plung'd into cold Water) to half that degree which he mentions, namely to 70 times its natural extent, unless it were that the AEolipile he imploy'd was able to sustain a more vehement heat than ours (which yet we kept in so great an one, that once the Soder melting, it fell asunder into the two Hemispheres it consists of.)

The fore-mentioned way of weighing the Air by the help of an AEolipile, seems somewhat more exact than that which Mersennus used, In that in ours the AEolipile was not weighed, till it was cold; whereas in his, being weighed red hot, it is subject to lose of its substance in the cooling, for (as we have elsewhere noted on another occasion) Copper heated red hot, is wont in the cooling to throw off little thin seales in such plenty, that having purposely watched a Copper AEolipile during its refrigeration, we have seen the place round about it almost covered with those little scales it had every way scatter'd: which, however they amount not to much, ought not to be over-looked, when 'tis so light a Body as Air, that is to be weighed. We will not examine whether, the AEolipile in cooling may not receive some little increment of weight, either from the vapid or saline Steams that wander up and down in the Air: But we will rather mention, that (for the greater exactness) we imployed to weigh our AElipile, both when fill'd only with Air and when replenish'd with Water, a pair of Scales that would turn (as they speak) with the fourth part of a grain.

As to the proportion of weight betwixt Air and Water, some learned men have attempted it by ways so unaccurate that they seem to have much mistaken it. For (not to mention the improbable accounts of Kepler and others.) The learned and diligent Ricciolus, having purposely endeavoured to investigate this proportion by means of a thin bladder, estimates the weight of the Air to that of the Water to be as one to ten thousand, or there abouts. And indeed I remember that having formerly, on a certain occasion, weighed a large bladder full of Air, and found [Page] it when the Air was all squeesed out, to have contained fourteen grains of Air. I found the same bladder afterwards fill'd with Water to contain very near 14 pound of that liquor: according to which account, the proportion of Air to Water was almost as a grain to a pound, that is, as one, to above 7600. To this we may add, that on the other side, Galileo himself using another, (but an unaccurate way too,) defined the Air to be in weight to Water, but as one to 4 hundred. But the way formerly proposed of weighing the Air by an AEolipile, seems by great odds more exact; and (as far as we could ghess) seemed to agree well enough with the Experiment made in our Receiver. Wherefore it will be best to trust our AEolipile in the enquiry we are about. And according to our observations the water it contained amounting to one and twenty ounces and an half, and as much Air as was requisite to fill it weighing eleven grains, the proportion in gravity of Air to Water of the same bulk will be as one to 938. And though we could not fill the AEolipile with water, so exactly as we would, yet in regard we could not neither as perfectly as we would, drive the Air out of it by heat, we think the proportion may well enough hold: but those that are delighted with round numbers (as the phrase is) will not be much mistaken if they reckon Water to be near a thousand times heavier than Air. And (for farther proof that we have made the proportion betwixt these two Bodies rather greater than lesser than indeed it is: and also to confirm our former observation of the weight of the Air) we will add, That, having another time put some Water into the AEolipile before we set it on the fire, that the copious vapours of the rarefied liquor might the better drive out the Air, we found, upon tryal carefully made, that when the AEolipile was refrigerated, and the included vapours were by the cold turned again into Water (which could not have happen'd to the Air, that the preceding Steams expelled) the Air, when it was let in, increas'd the weight of the AEolipile as much as before, namely, Eleven Grains; though there were already in it twelve Drachms and a half, besides a couple of Grains of Water, which remained of that we had formerly put into it to drive out the Air.

[Page] Mersennus indeed tells us, that by his account Air is in weight to Water, as 1 to 1356. And adds, that we may, without any danger, believe that the gravity of Water to that of Air of a like bulk, is not less than of 1300 to 1. And consequently that the quantity of Air to a quantity of Water equiponderant thereto, is as 1300 to 1. But why we should relinquish our own carefully repeated tryals, I see not. Yet I am unwilling to reject those of so accurate and usefull a Writer: And therefore shall propose a way of reconciling our differing Observations, by presenting, that the discrepance between them may probably arise from the differing consistence of the Air at London and at Paris: For our Air being more cold and moist, than that which Your Lordship now breaths, may be suppos'd also to be a fourth or fifth part more heavy. I leave it to be consider'd, whether it be of any moment that our Observations were made in the midst of Winter, whereas his were perhaps made in some warmer time of the Year. But I think it were not amiss, that, by the method formerly propos'd, the gravity of the Air were observ'd both in several Countries, and in the same Country, in the several Seasons of the Year and differing Temperatures of the Weather. And I would give something of value to know the weight of such an AEolipile as ours full of Air, in the midst of Winter in Nova Zembla, if that be true which we formerly [...]ook notice of, namely, That the Hollanders, who Wintered there, found that Air so thick that their Clock would not go.

If Your Lordship should now ask me, if I could not by the help of these, and our other Observations, decide the Controversies of our Modern Mathematicians about the height of the Air or Atmosphere, by determining how high it doth indeed reach: I should answer, That though it seems easie enough to shew that divers Famous and Applauded Writers have been mistaken in assigning the height of the Atmosphere: Yet it seems very difficult precisely to define of what height it is. And because we have hitherto but lightly touch'd upon a matter of such importance, we presume it will not be thought impertinent, upon this occasion, to annex something towards the Elucidation of it.

[Page]What we have already try'd and newly set down, allows us to take it for granted, that (at least about London) the proportion of gravity betwixt Water and Air, of equal bulk, is as of a thousand to one.

The next thing therefore that we are to enquire after, in order to our present design, is the difference in weight betwixt Water and Quick-silver: And though this hath been defin'd already by the Illustrious Verulam, and some other inquisitive Persons, that have compared the weight of several Bodies, and cast their Observations into Tables, yet we shall not scruple to annex our own tryals about it: Partly, because we find Authors considerably to disagree; partly, because we used exacter Scales, and a somewhat more wary method than others seem to have done: And partly also, because having prosecuted our inquiry by two or three several ways; the small difference between the events may assure us that we were not much mistaken.

We took then a Glass Pipe, of the form of an inverted Siphon, whose shape is delineated in the sixteenth Figure: And pouring into it a quantity of Quick-silver, we held it so, that the superficies of the Liquor, both in the longer and shorter leg, lay in a Horizontal Line, denoted in the Scheme by the prick'd Line E F; then pouring Water into the longer Leg of the Siphon, till that was almost fill'd, we observ'd the surface of the Quick-silver in that Leg to be, by the weight of the Water, depressed, as from E to B; and in the shorter Leg, to be as much impell'd upwards as from F to C: Whereupon having formerly stuck marks, as well at the point B, as at the opposite point D, we measur'd both the distance D C to have the height of the Cylinder of Quick-silver, which was raised above the point D (level with the surface of the Quick-silver in the other Leg) by the weight of the Water, and the distance B A which gave us the height of the Cylinder of Water. So that the distance D C amounting to 2 13\54 Inches, and the height of the Water amounting 30 45\54 Inches; and the whole numbers on both sides, which the annexed Fractions being reduc'd to improper Fractions of the same denomination, the proportion, appear'd to be (the denominators [Page] being left out as equal on both sides) as 121 to 1665; or by reduction, as one to 92/121.

Besides this unusual way of determining the gravity of some things, we measur'd the proportion betwixt Quick-silver and Water, by the help of so exact a ballance, as looseth its AEquilibrium by the hundredth part of a Grain. But because there is wont to be committed an oversight in weighing Quick-silver and Water, especially if the Orifice of the Vessel wherein they are put be any thing wide, in regard that men heed not that the surface of Water in Vessels will be concave, but that of Quick-silver notably convex or protuberant: To avoid this usual oversight (I say) we made use of a Glass bubble, blown very thin at the Flame of a Lamp, that it might not be too heavy for the Ballance, and terminating in a very slender neck wherein the concavity or convexity of a Liquor could not be considerable: This Glass weighing 23½ Grains, we fill'd almost with Quick-silver, and fastning a mark over against the middle of the protuberant Superficies as near as our Eyes could judge, we found that the Quick-silver alone weighed 299 7/12 Grains; Then the Quick-silver being pour'd out, and the same Glass being fill'd as full of common Water, we found the Liquor to weigh 21⅞ Grains. Whereby it appear'd the weight of Water to Quick-silver, is as one to 13 19/28: Though our Illustrious Verulam (questionless not for want of Judgment or Care, but of exact Instruments) Makes the proportion betwixt those two Liquors to be greater than of 1 to 17. And to add, that upon the bye, since Quick-silver and well rectified Spirit of Wine, are (how justly I say not) accounted, the one the heaviest, and the other the lightest of Liquors; we thought to fill the same Glass, and with the same Scales to observe the difference betwixt them, which we found to be as of 1 to 16 641/1084; whereby it appear'd, That the difference betwixt Spirit of Wine, that may be made to burn all away, (such as was ours) and common Water, is as betwixt 1 and 1 44/171.

We might here take occasion to admire, that though Water (as appear'd by the Experiment formerly mention'd of the Pewter Vessel) seems not capable of any considerable condensation, [Page] and seems not to have interspersed in it any store of Air; yet Quick-silver, of no greater bulk than Water, should weigh near fourteen times as much. But having only pointed at this as a thing worthy of consideration, we will proceed in our inquiry after the height of the Atmosphere: And to avoid the trouble of Fractions, we will assume, that Quick-silver is fourteen times as heavy as Water, since it wants so little of being so.

Wherefore, having now given us the proportion of Air to Water, and Water to Quick-silver, it will be very easie to find the proportion betwixt Air and Quick-silver, in case we will suppose the Atmosphere to be uniformly of such a consistence as the Air we weighed here below. For since our Engine hath sufficiently manifested that 'tis the AEquilibrium with the external Air, that in the Torricellian Experiment keeps the Quick-silver from subsiding; And since, by our accurate Experiment formerly mention'd, it appears that a Cylinder of Mercury, able to ballance a Cylinder of the whole Atmosphere, amounted to near about thirty Inches; and since, consequently we may assume the proportion of Quick-silver to Air to be as fourteen thousand to one; it will follow, that a Cylinder of Air, capable to maintain an AEquilibrium, with a Mercurial Cylinder of two Foot and an half in height, must amount to 35000 Feet of our English measure; and consequently (reckoning five Foot to a Geometrical Pace, and one thousand such Paces to a Mile) to seven full Miles.

But this (as we lately intimated) proceeds upon the supposition, that the Air is every where of the same consistence that we found it near the surface of the Earth; but that cannot with any safety be concluded, not only for the reason I find to have been taken notice of by the Ancients, and thus exprest in Seneca. Omnis Aër (says he) quo propior est terris hoc crassior; quemadmodum in aqua & in omni humore faex Senec. Nat. quest. lib. 4. cap. 10. ima est, ita in Aëre spississima-quae (que) desidunt, but much more, because the springy Texture of the Aerial Corpuscles; makes them capable of a very great compression, which the weight of the incumbent part of the Atmosphere is very sufficient [Page] to give those that be undermost and near the surface of the Earth. And if we recall to mind those former Experiments, whereby we have manifested, That Air, much rarefied without heat, may easily admit a farther rarefaction from heat, and that the Air, even without being expanded by heat, is capable of being rarefied to above one hundred and fifty times the extent it usually possesseth here below; How can it be demonstrated that the Atmosphere may not, for ought we know, or at least for ought can be determin'd by our Statical and Mechanical Experiments, rise to the height of Five and twenty German Leagues, if not of some hundred of common Miles?

And this conjecture it self may appear very injurious to the height whereunto Exhalations may ascend, if we will allow that there was no mistake in that strange Observation made at Tolouse in a clear Night in August, by the diligent Mathematician Emamuel Magnan, and thus Recorded by Ricciolus, for I have not at hand the Author's own Book: Vidit (says he) ab hora undecima post meridiem Ricciol. Alma. Nov. Tom. 2. lib. 10. sect. 6. prop. 50. Ex Magnan. lib. 1. Perspectivae horariae prop. 38. usque ad mediam noctem Lunâ infra horizontem positâ, nubeculam quandam lucidam prope Meridianum fere usque ad Zenith diffusam quae consideratis omnibus non poterat nisi à sole illuminari; ideoque altior esse debuit tota umbra terrae. Addit (continues Ricciolus) simile quid evenisse Michaeli Angelo Riccio apud Sabinos versanti nempe viro in Mathesi eruditissimo.

Various Observations made at the feet, tops, and interjacent parts of high Mountains, might perchance somewhat assist us to make an estimate in what proportion, if in any certain one, the higher Air is thicker than the lower, and ghess at the difform consistence, as to laxity and compactness of the Air at several distances from us. And if the difficulties about the refractions of the Celestial Lights, were satisfactorily determin'd, that might also much conduce to the placing due limits to the Atmosphere (whose, Dimensions those Observations about Refractions seem hitherto much to contract.) But for the present we dare not pronounce any thing peremptorily concerning the height of it, [Page] but leave it to farther inquiry: contenting our selves to have manifested the mistake of divers eminent Modern Writers, who will not allow the Atmosphere to exceed above two or three Miles in height (as the Famous Kepler will not the Aër refractivus) and to have rendred a reason why in the mention we made in the Notes upon the first Experiment touching the height of the Atmosphere, we scrupled not to speak of it, as if it might be many Miles high.

EXPERIMENT XXXVII.

WE will now proceed to recite a Phaenomenon, which, though made amongst the first, we thought fit not to mention till after many others, that we might have the opportunity to observe as many Circumstances of it as we could, and so present Your Lordship at once, most of what we at several times have taken notice of concerning so odd a Phaenomenon.

Our Engine had not been long finish'd, when, at the first leisure we could steal from our occasions to make trial of it, we caused the Air to be pump'd out of the Receiver; and whilst I was busied in entertaining a Learned Friend that just then came to visit me, an Ingenious By-stander, thought he perceiv'd some new kind of Light in the Receiver, of which giving me hastily notice, my Friend and I presently observ'd, that when the Sucker was drawn down, immediately upon the turning of the Key, there appear'd a kind of Light in the Receiver, almost like a faint flash of Lightning in the Day-time, and almost as suddenly did it appear and vanish. Having, not without some amazement, observ'd divers of these apparitions of Light, we took notice that the Day was clear, the hour about ten in the Morning, that the only Window in the Room faced the North; and also, that by interposing a Cloak, or any opacous Body between the Receiver and the Window, though the rest of the Room were sufficiently enlightned, yet the flashes did not appear as before, unless the opacous Body were removed. But not being able on all these Circumstances to ground any firm Conjecture at the cause of this surprising Phaenomenon, as soon as Night [Page] was come, we made the Room very dark; and plying the Pump, as in the Morning, we could not, though we often try'd, find, upon the turning of the Key, so much as the least glimmering of Light; whence we inferred, that the flash appearing in the Receiver, did not proceed from any new Light generated there, but from some reflexions of the light of the Sun, or other Luminous Bodies plac'd without it; though whence the Reflexion should proceed, it pos'd us to conjecture.

Wherefore the next Morning, hoping to inform our selves better, we went about to repeat the Experiment, but though we could as well as formerly exhaust the Receiver, though the place wherein we made the trial was the very same; and though other Circumstances were resembling, yet we could not discover the least appearance of Light all that Day, nor on divers others on which trial was again fruitlesly made; nor can we to this very time be sure a Day before-hand that these Flashes will be to be seen in our great Receiver. Nay, having once found the Engine in a good humour (if I may so speak) to shew this trick, and sent notice of it to our Learned Friend Dr. Wallis, who express'd a great desire to see this Phaenomenon, though he were not then above a Bow-shoot off, and made haste to fatisfie his Curiosity; yet by that time he was come, the thing he came for was no longer to be seen; so that having vainly endeavoured to exhibit again the Phaenomenon in his prefence, I began to apprehend what he might think of me, when unexpectedly the Engine presented us a flash, and after that a second, and as many more, as suffic'd to satisfie him that we might very well confidently relate, that we have our selves seen this Phaenomenon, though not confidently promise to shew it others.

And this unsuccessfulness whereto our Experiment is liable, being such, that by all our watchfulness and trials, we could never reduce it to any certain Rules or Observations; since in all constitutions of the Weather, times of the Day, &c. It will sometimes answer, and sometimes disappoint our expectations; We are much discourag'd from venturing to frame an Hypothesis to give an account of it: which if the Experiment did constantly [Page] succeed, might the more hopefully be attempted; by the help of the following Phaenomena laid together: some of them produc'd upon trials purposely made to examine the validity of the conjectures, other trials had suggested.

First then we observ'd, that the Apparition of Light may be made as well by Candle-light, as by Day-light; and in whatever position the Candle be held, in reference to the Receiver, as on this or that hand of it, above it, beneath it, or any other way, provided the beams of Light be not hinder'd from falling upon the Vessel.

Next, we noted that the flash appears immediately upon the turning of the Key, to let the Air out of the Receiver into the emptied Cylinder, in so much that I remember not that when at any time in our great Receiver, the Stop-cock was open'd before the Cylinder was exhausted (whereby it came to pass that the Air did rather descend, than rush into the Cylinder) the often mentioned flash appear'd to our eyes.

Yet, we farther observ'd, that when instead of the great Receiver we made use of a small Glass, not containing above a pound and a half of Water, the Phaenomenon might be exhibited though the Stop-cock were open, provided the Sucker were drawn nimbly down.

We noted too, that when we began to empty the Receiver, the appearances of Light were much more conspicuous than towards the latter end, when little Air at a time could pass out of the Receiver.

We observed also, that when the Sucker had not been long before well Oyl'd, and instead of the great Receiver, the smaller Vessel above-mention'd was emptied; We observ'd, I say, that then, upon the opening of the Stop-cock, as the Air descended out of the Glass into the emptied Cylinder, so at the same time there ascended out of the Cylinder into the Vessel a certain steam, which seem'd to consist of very little Bubbles, or other minute Corpuscles thrown up from the Oyl, rarefied by the attrition it suffered in the Cylinder. For at the same time that these Steams ascended into the Glass, some of the same kind manifestly [Page] issued out like a little Pillar of Smoke at the Orifice of the Valve, when that was occasionally opened. And these Steams frequently enough presenting themselves to our view, we found, by exposing the Glass to a clear Light, that they were wont to play up and down in it, and so by their whitishness, to emulate in some measure the apparition of Light.

For we likewise sometimes found, by watchfull observation, that when the Flash was great, not only at the very instant the Receiver lost of its transparency, by appearing full of some kind of whitish substance; but that for some short time after the sides of the Glass continued somewhat opacous, and seem'd to be darken'd, as if some whitish Steam adher'd to the inside of them.

He that would render a Reason of the Phaenomenon, whereof all these are not all the Circumstances, must do two things; whereof the one is difficult, and the other little less than impossible: For he must give an account not only whence the appearing whiteness proceeds, but wherefore that whiteness doth sometimes appear, and sometimes not.

For our part, we freely confess our selves at a loss about rendering a Reason of the less difficult part of the Problem: And though Your Lordship should ev'n press us to declare what Conjecture it was, that the above recited Circumstances suggested to us, we should propose the thoughts we then had, no otherwise than as bare Conjectures.

In case then our Phaenomenon had constantly and uniformly appear'd, we should have suspected it to have been produc'd after some such manner as follows.

First, we observ'd that, thought that which we saw in our Receiver seem'd to be some kind of Light, yet it was indeed but a whiteness which did (as hath already been noted) opacate (as some speak) the inside of the Glass.

Next we consider'd, that our common Air abounds with Particles, or little Bodies, capable to reflect the beams of Light. Of this we might easily give divers proofs, but we shall name but two: The one, that vulgar observation of the Motes that appear [Page] in multitudes swimming up and down in the Air, when the Sunbeams shooting into a Room, or any other shady place, discover them, though otherwise the Eye cannot distinguish them from the rest of the Air: The other proof we will take from what we (and no doubt very many others) have observ'd, touching the Illumination of the Air in the Night. And we particularly remember, that, being at some distance from London one Night, that the People, upon a very welcome occasion, testified their Joy by numerous Bon-fires; though, by reason of the Interposition of the Houses, we could not see the Fires themselves, yet we could plainly see the Air all enlighten'd over and near the City; which argu'd, that the lucid Beams shot upwards from the fires, met in the Air with Corpuscles opacous enough to reflect them to our Eyes.

A third thing that we considered, was, That white may be produc'd (without excluding otherways, or denying invisible Pores in the solidest Bodies) when the continuity of a Diaphanous Body happens to be interrupted by a great number of surfaces, which, like so many little Looking-glasses, do confusedly represent a multitude of little and seemingly contiguous Images of the lucid Body. We shall not insist on the explanation of this, but refer You for it to what we have said in another Paper (touching Colours.) But the Instances that seem to prove it are obvious: For Water or whites of Eggs beaten to froth, do lose their transparency and appear white. And having out of one of our lessers Receivers carefully drawn out the Air, and so order'd it, that the hole by which the Water was to get in, was exceeding small, that the Liquor might be the more broken in its passage thorow it, we observ'd with pleasure, That, the Neck being held under Water, and the little hole newly mention'd being open'd, the Water that rushed in was so broken, and acquired such a multitude of new Surfaces, that the Receiver seem'd to be full rather of Milk than Water. We have likewise found out, That by heating a lump of Crystal to a certain degree, and quenching it in fair Water, it would be discontinu'd by such a multitude of Cracks, (which created new Surfaces within it) that [Page] though it would not fall asunder, but retain its former shape, yet it would lose its transparency, and appear white.

Upon these Considerations, My Lord, and some others, it seem'd not absur'd to imagine, That upon the rushing of the Air out of the Receiver into the empty'd Cylinder, the Air in the Receiver being suddenly and vehemently expanded, the Texture of it was as suddenly alter'd, and the parts made so to shift places (and perhaps some of them to change postures) as during their new and vehement motion and their varied situation, to disturb the wonted continuity, and so the Diaphaneity of the Air; which (as we have already noted) upon its ceasing to be a transparent Body, without the interposition of colour'd things, must easily degenerate into white.

Several things there were that made this Conjecture seem the less improbable. As first, That the whiteness always appear'd greater when the exsuction began to be made, whilst there was store of Air in the Receiver, than when the Air was in great part drawn out. And next, That, having exhausted the Receiver, and apply'd to the hole in the Stop-cock a large bubble of clear Glass, in such a manner, that we could at pleasure let the Air pass out at the small Glass into the great one, and easily fill the small one with Air again, We observ'd with pleasure, That, upon the opening the passage betwixt the two Glasses, the Air in the smaller having so much room in the greater to receive it, the Dissilition of that Air was so great, that the small Viol seem'd to be full of Milk; and this Experiment we repeated several times. To which we may add, That, having provided a small Receiver, whose upper Orifice was so narrow that I could stop it with my Thumb, I observ'd, that when, upon the exsuction of the Air, the capacity of the Glass appear'd white, if, by a sudden removal of my Thumb, I let in the outward Air, that whiteness would immediately vanish. And whereas it may be objected, That in the Instance formerly mention'd, Water turning from perspicuous to white, there intervenes the Air, which is a Body of a Heterogeneous nature, and must turn it into Bubbles to make it lose its transparency. We may borrow an Answer from an [Page] Experiment we deliver in another Treatise, where we teach, how to make two very volatile Liquors, which being gently put together, are clear as Rock-water, and yet will almost in a moment, without the sub-ingression of Air to turn them into Bubbles, so alter the disposition of their insensible parts, as to become a white and consistent Body. And this happens not as in the precipitation of Benjamin, and some other Resinous Bodies, which being dissolv'd in spirit of Wine, may, by the effusion of fair Water, be turn'd into a seemingly Milky substance. For this whiteness belongs not to the whole Liquor, but to the Corpuscles of the dissolv'd Gum, which after a while subsiding leave the Liquor transparent, themselves only remaining white: Whereas in our case, 'tis from the vary'd texture of the whole formerly transparent fluid Body, and not from this or that part, that this whiteness results: For the Body is white throughout, and will long continue so; and yet may, in process of time, without any addition, be totally reduc'd into a transparent Body as before.

But besides the Conjecture insisted on all this while, we grounded another upon the following Observation, which was, That having convey'd some smoke into our Receiver plac'd against a Window, we observ'd, that upon the exsuction of the Air, the Corpuscles that were swimming in it, did manifestly enough make the Receiver seem more opacous at the very moment of the rushing out of the Air: For considering that the whiteness, whose cause we enquire of, did but sometimes appear, it seem'd not impossible but that at such times the Air in the Receiver might abound with Particles, capable of reflecting the Light in the manner requisite to exhibite a white colour, by their being put into a certain unusual Motion. As may be in some measure illustrated by this, That the new motion of the freshly mention'd Fumes, made the inside of the Receiver appear somewhat darker than before: And partly by the nature of our formerly mention'd smoking Liquor, whose parts, though they seem'd transparent whilst they compos'd a Liquor, yet when the same Corpuscles, upon the unstopping of the Glass, were put into a new [Page] motion, and dispos'd after a new manner, they did opacate that part of the Air they mov'd in, and exhibited a greater whiteness than that which sometimes appears in our Pneumatical Vessel. Nor should we content our selves with this single Instance, to manifest, That little Bodies, which being rang'd after one manner, are Diaphanous and Colour-less, may, by being barely agitated, dispers'd, and consequently otherways rang'd, exhibit a colour, if we were not unwilling to rob our Collection of Experiments concerning Colours.

But, My Lord, I foresee You may make some Objections against our proposed ghess, which perhaps I shall scarce be able to answer, especially, if You insist upon having me render a Reason why our Phaenomenon appears not constantly.

I might indeed answer, that probably it would do so, if instead of our great Receiver we use such a small Viol as we have lately mention'd, wherein the Dissilition of the Air being much greater, is like to be the more conspicuous: Since I remember not that we ever made our trial with such small Vessels, without finding the expected whiteness to appear. But it would remain to be explicated, why in our great Receiver the Phaenomenon should sometimes be seen, and oftentimes not appear. And though that Conjecture which we last made should not be rejected, yet if we were farther press'd to assign a reason why the Air should abound with such Particles, as we there suppose, more at one time than another, we are not yet provided of any better Answer, than this general one, That the Air about us, (and much more that within the Receiver,) may be much alter'd by such causes as few are aware of: For, not to repeat those probable Arguments of this Assertion which we have occasionally mention'd here and there in the former part of this Epistle, we will here set down two or three Instances to verifie the same Proposition. First, I find that the Learned Josephus Acosta, among other Judicious Observations he made in America, hath this concerning the effects of some Joseph. Acosta's Nat. and Mor. Hyst. of the Indies, jib. 3. cap. 9. Winds: There are (saith he) Winds which naturally trouble the Water of the Sea, and [Page]make it green, and black; others, clear as Crystal. Next, we have observ'd, That though we convey'd into the Receiver our Scales, and the Pendula formerly mention'd, clean and bright; yet aster the Receiver had been empty'd, and the Air let in again, the gloss or lustre both of the one, and of the other, appear'd tarnish'd by a beginning rust. And in the last place, we will subjoyn an Observation we made some Years ago, which hath been heard of by divers Ingenious Men, and seen by some of them: We had, with pure Spirit of Wine, drawn a Tincture out of a certain Concrete which useth to be reckon'd among Mineral Bodies; And this Tincture being very pure and transparent, we did, because we put a great value upon it, put into a Crystal Viol which we carefully stopp'd, and lock'd up in a Press among some other things that we specially priz'd. This Liquor being a Chymical Rarity, and besides very defecate, and of a pleasing Golden colour; we had often occasion to look upon it, and so to take notice, that one time it seem'd to be very much troubled, and not clear as it was wont to be: Whereupon we imagined, that though it would be something strange, yet it was not impossible, that some Precipitation of the Mineral Corpuscles was then happening, and that thence the Liquor was opacated. But, finding after some days that though the expected Precipitation had not been made, yet the Liquor, retaining its former vivid Colour, was grown clear again as before; we somewhat wondered at it, and locking it up again in the same Press, we resolved to observe, both whether the like changes would again appear in our Tincture; and whether in case they should appear, they would be ascribable to the alterations of the Weather. But though, during the greatest part of a Winter and a Spring, we took pleasure to observe, how the Liquor would often grow turbid, and after a while clear again: Yet we could not find that these Mutations depended upon any that were manifest in the Air, which would be often dark and clouded, when the Tincture was clear and transparent; as on the other side, in clear Weather the Liquor would appear sometimes troubled, and more opacous. So that being unable to give an account of [Page] these odd changes in our Tincture (which we suppose we have not yet lost, though we know not whether it hath lost its fickle Nature) either by those of the Air, or any thing else that occurr'd to our thoughts; we could not but suspect, that there may be in divers Bodies, as it were Spontaneous Mutations, that is, such changes as depend not upon manifest Causes. But, My Lord, what hath been all this while said concerning our Phaenomenon, is offer'd to You, not as containing a satisfactory account of it, but to assist You to give Your self one.

EXPERIMENT XXXVIII.

WE took a Glass Vessel, open at the top, and into it we put a mixture of Snow and common Salt, (such a mixture as we have in another Treatise largely discoursed of) and into the midst of this mixture we set a Glass, of a Cylindrical form, closely stopp'd at the lower end with Plaister, and open at the upper, at which we fill'd it with common Water. These things being let down into the Receiver, and the Pump being set on work, the Snow began to melt somewhat faster than we expected; Whether upon the account of the exsuction of the Air, or because there was but little of the Snow, or whether for any other Reason, it appear'd doubtfull. But however, by that time the Receiver had been considerably exhausted, which was done in less than ¼ of an hour, we perceived the Water near the bottom of the Glass Cylinder to Freeze, and the Ice by a little longer stay, seem'd to encrease, and to rise somewhat higher than the surface of the surrounding Liquor, whereinto almost all the Snow and Salt were resolv'd. The Glass being taken out, it appear'd that the Ice was as thick as the inside of the Glass it fill'd, though into that I could put my Thumb. The upper surface of the Ice was very concave, which whether it were due to any unheeded accident, or to the exsuction of the Air, we leave to be determin'd by farther trial. And lastly, the Ice held against the Light, appear'd not destitute of Bubbles, though some By-standers thought they were fewer than would have been found if the Water had been frozen in the open Air. The [Page] like Experiment we try'd also another time in one of our small Receivers, with not unlike success.

And on this occasion, My Lord, give me leave to propose a Problem, which shall be this: Whence proceeds that strange force that we may sometimes observe in frozen Water, to break the Bodies that imprison it, though hard and solid? That there is such a force in Water expos'd to Congelation, may be gathered not only from what may be often observ'd in Winter, of the bursting of Glasses too close stopp'd, fill'd with Water or aqueous Liquors, but by Instances as much more considerable as less obvious. For I remember, that an Ingenious Stone-cutter not long since complain'd to me, That sometimes, through the negligence of Servants, the Rain being suffered to soak into Marble Stones, the supervening violent Frosts would burst the Stones, to the Possessour's no small damage. And I remember another Trades-man, in whose House I had Lodgings, was last Winter complaining, that even Implements made of Bellmetal, being carelesly expos'd to the wet, have been broken and spoil'd by the Water, which, having gotten into the little Cavities and Crannies of the Metal, was there afterwards frozen and expanded into Ice. And to these Relations, we can add one of the formerly mention'd Cabaeus's, whereby In lib. 4. Meleor. Arist. they not only may be confirm'd; but are surpass'd: For he tells us, That he saw a huge Vessel of exceeding hard Marble, split asunder by congeal'd Water, whose rarefaction, saith our Author, prov'd so vehement, that the hardness of the Stone yielded to it; and so a vessel was broken, which would not have been so by 100 Yoke of Oxen drawing it several ways. I know, My Lord, that to solve this Problem, it will be said, That Congelation doth not (as is commonly, but erroneously presum'd) reduce Water into less room than it possess'd before, but rather makes it take up more. And I have elsewhere prov'd by particular Experiments, That whether or no Ice may be truly said to be Water rarefi'd (for that seems questionable) it may be said to take up more room than the Water did before Glaciation. But though we grant that freezing makes Water [Page] swell, yet, how cold (which in Weather-Glasses manifestly condenseth the Air) should expand either the Water, or the intercepted Air so forcibly, as to perform such things as we have newly related, will yet remain a Problem.

EXPERIMENT XXXIX.

WE took an Oval Glass, clear and (lest it should break) pretty strong, with a short Neck at the obtuser end; through this Neck, we thrust almost to the bottom, a Pipe of Glass, which was closely cemented to the newly mention'd Neck, the upper part of which Pipe, was drawn in some places more slender than a Crows Quill, that the changes of the Air in that Glass Egg might be the more conspicuous; Then there was convey'd into the Glass five or six Spoon-fulls of Water, part of which, by blowing Air into the Egg, was rais'd into the abovemention'd slender part of the Pipe, so that the Water was interpos'd between the external Air, and that included in the Egg. This Weather glass (delineated in the fourteenth Figure) was so plac'd, and clos'd up in the cavity of one of our small Receivers, that only the slender part of the Pipe, to the height of four or five Inches, passing thorow a hole in the Cover remain'd expos'd to the open Air.

The Pump being set a work, upon the exsuction of the Air, the Water in the Pipe descended about a quarter of an Inch, and this upon two or three reiterated trials; which seem'd sufficiently to argue, that there was no heat produc'd in the Receiver upon the exsuction of the Air: For even a little heat would probably have been discover'd by that Weather-glass, since upon the bare application of my hand to the outside of the Receiver, the warmth having after some time been communicated or propagated through both the Glasses, and the interval betwixt them, to the imprison'd Air, did so rarefie that, as to inable it, by pressing upon the subjacent Water, to impel that in the Pipe very many times as far as it had fallen downwards upon the exsuction of the Air.

Yet shall not we conclude, that in the cavity of the Receiver [Page] the cold was greater after the exsuction of the Air than before.

For if it be demanded what then could cause the fore-mention'd subsiding of the Water? it may be answered, That probably it was the reaching of the Glass Egg, which, upon the exsuction of the ambient Air, was unable to resist altogether as much as formerly the pressure of the included Air, and of the Atmosphere, which, by the intervention of the Water, press'd upon its concave surface: Which seem'd probable, as well by what was above deliver'd, in the Experiment about the breaking of the Glass by the force of the Atmosphere; as by this notable Circumstance (which we divers times observ'd) That when by drawing the Air out of the Receiver, the Water in the Pipe was subsided, upon the re-admission of the external Air, to press against the convex surface of the Egg, the Water was presently re-impell'd to its former height: Which would perhaps appear less strange to Your Lordship, if You had yet seen, what we have heretofore taught in another Treatise, concerning the Spring that may be discover'd in Glass, as rigid and inflexible a Body as it is generally esteem'd. And in the mean while it may serve the turn, to cause a Glass Egg to be blown exceeding thin; and then, having broken it, try how far you can by degrees bend some narrow parts of it; and how readily, upon the removal of what kept it bent, it will restore it self to its former state or posture. But to return to our Experiment: From thence it seems probable, either that there succeeds no Body in the room of the Air drawn out of our Receiver; or that it is not every Matter that is suotle enough readily to pass through the Pores of Glass, that is always agitated enough to produce Heat where ever it is plentifully found. So that if no Vacuum be to be admitted, this Experiment seems to invite us to allow a great disparity, either as to bulk, or as to agitation, or as to both, betwixt some parts of the Etherial substance, and those that are wont here below to produce Heat and Fire.

We try'd also what Operation the drawing out of the Air would have upon Camphire, that being a Body, which, though not a [Page] Liquor, consists of such Volatile or Fugitive parts, that without any greater agitation than that of the open Air it self, they will copiously flie away. But we sound not that even this loose Body was sensibly alter'd by the exsuction of the ambient Air.

EXPERIMENT XL.

IT may seem well worth trying, whether or no in our exhausted Glass the want of an ambient Body, of the wonted thickness of Air, would disable even light and little Animals, as Bees, and other winged Insects, to fly. But though we easily foresaw how difficult it would be to make such an Experiment; yet not to omit our endeavours: We procur'd a large Flesh Fly, which we convey'd into a small Receiver. We also another time shut into a great Receiver a Humming Bee, that appear'd strong and lively, though we had rather have made the trial with a Butter-fly, if the cold Season would have permitted us to find any. Since the writing of this XLth Experiment, we procur'd a white Butter-Fly, and inclosed it in one of our smaller Receivers, where, though at first he fluttered up and down, yet presently, upon the exsuction of the Air, he fell down as in a swoon, retaining no other motion than some little trembling of the Wings. The Fly, after some exsuctions of the Air, dropp'd down from the side of the Glass whereon she was walking: But, that the Experiment with the Bee might be the more instructive, we convey'd in with her a bundle of Flowers, which remain'd suspended by a string near the upper part of the Receiver: And having provok'd the Bee, we excited her to flie up and down, the capacity of the Vessel, till at length, as we desir'd, she lighted upon the Flowers; whereupon we presently began to draw out the Air, and observ'd, That though for some time the Bee seem'd to take no notice of it, yet within a while after she did not flie, but fall down from the Flowers; without appearing to make any use of her Wings to help her self. But whether this fall of the Bee, and the other Insect, proceeded from the mediums being too thin for them to flie in, or barely from the weakness, and as it were swooning of the Animals themselves, you will easily gather from the following Experiment.

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EXPERIMENT XLI.

TO satisfie our selves in some measure, about the account upon which Respiration is so necessary to the Animals, that Nature hath furnished with Lungs, we took (being then unable to procure any other lively Bird, small enough to be put into the Receiver) a Lark, one of whose Wings had been broken by a shot, of a Man that we had sent to provide us some Birds for our Experiment; but notwithstanding this hurt, the Lark was very lively, and did, being put into the Receiver, divers times spring up in it to a good height. The Vessel being hastily, but carefully clos'd, the Pump was diligently ply'd, and the Bird for a while appear'd lively enough; but upon a greater exsuction of the Air, she began manifestly to droop and appear sick, and very soon after was taken with as violent and irregular Convulsions, as are wont to be observ'd in Poultry, when their heads are wrung off: For the Bird threw her self over and over two or three times, and dyed with her Breast upward, her Head downwards, and her Neck awry. And though upon the appearing of these Convulsions, we turn'd the Stop-cock, and let in the Air upon her, yet it came too late; whereupon casting our Eyes upon one of those accurate Dyals that go with a Pendulum, and were of late ingeniously invented by the Noble and Learned Hugenius, we found that the whole Tragedy had been concluded within ten Minutes of an hour, part of which time had been imploy'd in cementing the Cover to the Receiver. Soon after we got a Hen-sparrow which being caught with Bird-lime was not at all hurt; when we put her into the Receiver, almost to the top of which she would briskly raise her self, the Experiment being try'd with this Bird, as it was with the former, she seemed to be dead within seven minutes, one of which were imployed in cementing on the Cover: But upon the speedy turning of the Key, the fresh Air flowing in, began slowly to revive her, so that aster some pantings she opened her eyes, and regain'd her feet, and in about a ¼ of an hour after, threatned to make an escape at the top of the Glass, [Page] which had been unstopped to let in the fresh Air upon her: But the Receiver being closed the second time, she was killed with violent Convulsions, within five Minutes from the beginning of the Pumping.

A while after we put in a Mouse, newly taken, in such a Trap as had rather affrighted than hurt him; whilst he was leaping up very high in the Receiver, we fasten'd the Cover to it, expecting that an Animal used to live in narrow holes with very little fresh Air, would endure the want of it better than the lately mentioned Birds: But though, for a while after the Pump was set a work, he continued leaping up as before; yet, 'twas not long ere he began to appear sick and giddy, and to stagger: after which he fell down as dead, but without such violent Convulsions as the Bird died with. Wherepon, hastily turning the Key, we let in some fresh Air upon him, by which he recovered, after a while, his senses and his feet, but seemed to continue weak and sick: But at length, growing able to skip as formerly, the Pump was plyed again for eight minutes, about the middle of which space, if not before a very little Air by a mischance got in at the Stop-cock; and about two minutes after that, the Mouse divers times leap'd up lively enough, though after about two minutes more he fell down quite dead, yet with Convulsions far milder than those wherewith the two Birds expired. This alacrity so little before his death, and his not dying sooner than at the end of the eighth minute, seemed ascribable to the Air (how little soever) that slipt into the Receiver. For the first time, those Convulsions (that, if they had not been suddenly remedied, had immediately dispatch'd him) seised on him in six minutes after the Pump began to be set a work. These Experiments seemed the more strange, in regard that during a great part of those few minutes the Engine could but considerably rarefie the Air (and that too, but by degrees) and at the end of them there remained in the Receiver no inconsiderable quantity; as may appear by what we have formerly said of our not being able to draw down Water in a Tube, within much less than a Foot of the bottom: With which we likewise consider'd, that by the [Page] exsuction of the Air and interspersed Vapours, there was left in the Receiver a space some hundreds of times exceeding the bigness of the Animal, to receive the fuliginous Steams, from which, expiration discharges the Lungs; and, which in the other cases hitherto known, may be suspected, for want of room, to stifle those Animals that are closely pen'd up in too narrow Receptacles.

I forgot to mention, that having caus'd these three Creatures to be open'd, I could, in such small Bodies, discover little of what we sought for, and what we might possibly have found in larger Animals; for though the Lungs of the Birds appear'd very red, and as it were inflam'd, yet that colour being usual enough in the Lungs of such winged Creatures, deserves not so much our notice, as it doth, That in almost all the destructive Experiments made in our Engine, the Animals appear'd to die with violent Convulsive motions: From which, whether Physicians can gather any thing towards the discovery of the Nature of Convulsive Distempers, I leave to them to consider.

Having proceeded thus far, though (as we have partly intimated already) there appear'd not much cause to doubt, but that the death of the fore-mention'd Animals proceeded rather from the want of Air, than that the Air was overclogg'd by the steams of their Bodies, exquisitely pen'd up in the Glass; yet I, that love not to believe any thing upon Conjectures, when by a not over-difficult Experiment I can try whether it be true or no, thought it the safest way to obviate Objections, and remove Scruples, by shutting up another Mouse as close as I could in the Receiver, wherein it lived about three quarters of an hour; and might probably have done so much longer, had not a Virtuoso of quality, who in the mean while chanc'd to make me a Visit, desir'd to see whether or no the Mouse could be kill'd by the exsuction of the ambient Air whereupon we thought fit to open, for a little while, an intercourse betwixt the Air in the Receiver, and that without it, that the Mouse might thereby (if it were needfull [Page] for him) be refresh'd, and yet we did this without uncementing the Cover at the top, that it might not be objected, that perhaps the Vessel was more closely stopp'd for the exsuction of the Air than before.

The Experiment had this event, that after the Mouse had liv'd ten Minutes, (which we ascrib'd to this that the Pump, for want of having been lately Oyled, could move but slowly, and could not by him that manag'd it, be made to work as nimbly as it was wont) at the end of that time he dy'd with Convulsive Fits, wherein he made two or three bounds into the Air, before he fell down dead.

Nor was I content with this, but for Your Lordships farther satisfaction, and my own, I caused a Mouse, that was very hungry, to be shut in all Night, with a Bed of Paper for him to rest upon: And to be sure that the Receiver was well clos'd, I caus'd some Air to be drawn out of it, whereby, perceiving that there was no sensible leak, I presently readmitted the Air at the Stop-cock, lest the want of it should harm the little Animal; and then I caused the Engine to be kept all Night by the Fire side, to keep him from being destroyed by the immoderate cold of the Frosty Night. And this care succeeded so well, that the next Morning I found that the Mouse not only was alive, but had devour'd a good part of the Cheese that had been put in with him. And having thus kept him alive full twelve hours, or better, we did, by sucking out part of the Air, bring him to droop, and to appear swell'd; and by letting in the Air again, we soon reduc'd him to his former liveliness.

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A Digression containing some Doubts touching Respiration.

I Fear Your Lordship will now expect, that to these Experiments I should add my Reflexions on them, and attempt, by their assistence, to resolve the difficulties that occur about Respiration; since at the beginning I acknowledg'd a farther enquiry into the Nature of that, to have been my design in the related Tryals. But I have yet, because of the inconvenient season of the Year, made so few Experiments, and have been so little satisfied by those I have been able to make, that they have hitherto made Respiration appear to me rather a more, than a less Mysterious thing, than it did before. But yet, since they have furnished me with some such new Considerations, concerning the use of the Air, as confirms me in my Diffidence of the truth of what is commonly believ'd touching that matter; That I may not appear sullen or lazy, I am content not to decline employing a few hours in setting down my Doubts, in presenting Your Lordship some Hints, and in considering whether the Tryals made in our Engine, will at least assist us to discover wherein the Deficiency lies that needs to be supplyed.

And this, My Lord, being all my present Design, I suppose You will not expect that (as if You knew not, or had forgotten what Anatomists are wont to teach) I should entertain You with a needless Discourse of the Organs of Respiration, and the variety of their Structure in several Animals; though if it were necessary, and had not been perform'd by others I should think, with Galen, that by treating of the Fabricks of living Bodies, I might compose Hymns to the wise Author of Nature, who, in the excellent contrivance of the Lungs, and other parts of (those admirable Engines) Animals, manifests himself to be indeed what the Eloquent Prophet most justly speaks him, Wonderfull in Councel, and excellent in working.

[Page]Nor shall we any farther meddle with those Controversies so much agitated among the Moderns, namely, Whether the motion of the Lungs in Respiration be their own, or but consequent to the motion of the Thorax, Diaphragme, and (as some Learned Men would have it) the Abdomen; And, Whence it is that the Air swells the Lungs in Inspiration, any farther than they may receive light from our Engine: But that it may appear what kind of service it is that may be expected from it on this occasion, we must premise a few Words to shew wherein the strength of the Objection we are to answer, lies: In favour then of those that would have the Lungs rather passive than active in the business of Respiration, it may against the common opinion be alledg'd, That as the Lungs being destitute of Muscles and of Fibres, are unfit to dilate themselves; so it appears, that without the motion of the Thorax they would not be fill'd with Air. Since as our Learned Friend Dr. Highmore hath well (and congruously, to what our selves have purposely tried) observed, if a live Dog have a great wound made in his Chest, the Lobes of the Lungs on that side of the Mediastinum will subside and lie still; the Thorax and the Lobes on the other side of the Mediastinum, continuing their former motion. And if suddenly at once the Muscles of the Chest be on both sides dissected, upon the Ingress of the Air, the whole Lungs, though untouch'd, will remain moveless, at least, as to any expansion or contraction of their substance.

To which we may add the Observation of the diligent Bartholinus, who affirms the like of the Diaphragme also, namely, That it being wounded, the Lungs will fall together, and the Respiration cease, which my Experiments oppose not, provided the Wound be any thing great. And indeed the Diaphragme seems the principal Instrument of ordinary and gentle Respiration, although to restrained Respiration (if I may so call it) the intercostal Muscles, and perhaps some others may be allowed eminently to concur. But the chief of the Controversies formerly pointed at, is not yet decided, namely, what it is that conveys the Air into the Lungs. For when, to counterballance all that [Page] hath been alledg'd, those that plead for the Lungs demand what it is that should bring the Air into the Lungs, if themselves do not attract it, their Antagonists disagree about the Reply. For when to this question some of the best Modern Philosophers answer, That by the dilatation of the Chest the contiguous Air is thrust away, and that pressing upon the next Air to it, and so onwards, the Propulsion it continued till the Air be driven into the Lungs, and so dilate them: When this (I say) is answered, it is Objected even by Bartholine himself, as a convincing Reply, that, according to this Doctrine, a Man could not fetch his Breath from a great Vessel full of Air, with a slender Neck, because, that when his Mouth covers the Orifice of the Neck, the dilatation of his Thorax could not propell the Air in the Vessel into his Lungs, by reason of its being separated by the inclosing Vessel from the ambient Air; and yet, say they, Experience witnesseth, that out of such a Vessel a Man may suck Air. But of this difficulty our Engine furnisheth us with an easie Solution, since many of: the former Experiments have manifested, That in the case proposed, there needs not be made any (though 'tis true that in ordinary Respiration there is wont to be made some) propulsion of the Air by the swelling Thorax or Abdomen into the Lungs; since upon the bare Dilatation of the Thorax, the Spring of that internal Air, or halituous substance that is wont to possess as much of the cavity of the Chest as the Lungs fill not up, being much weaken'd, the external and contiguous Air must necessarily press in at the open Wind pipe into the Lungs, as finding there less resistance than any where else about it.

And hence (by the way) we may derive a new assistance to judge of that famous Controversie disputed among Naturalists and Physicians, ever since Galen's time, some maintaining that the Chest, with the contained Lungs, may be resembled to a pair of Bellows, which comes therefore to be fill'd because it was dilated: And others pleading to have the comparison made to a Bladder, which is therefore dilated because it is fill'd. For as to the Thorax, it seems evident from what hath been lately said, that [Page] it, like a pair of Bellows, happens to be partly fill'd with Air, but because it was dilated: But as for the Lungs themselves, who want Fibres to distend them, they may fitly enough be compar'd to a Bladder; since they are dilated by being fill'd, namely, by that Air which rusheth into them upon the dilatation of the Chest, in whose increased cavity it finds (as we freshly noted) less resistance to its Spring than elsewhere. And this brings into my mind that strange Observation of Nicolaus Fontanus, a Physician at Amsterdam, who testifieth, That in a Boy of the same Town, four years old, there was found, instead of Lungs, a certain Membranous Bladder; which being fill'd with Wind, and furnish'd with little Veins, had its origination from the Wind-Pipe it self; which being suppos'd true, how well it will agree with most of the Opinions touching Respiration, I leave to be consider'd.

And thus may the grand Objection of Bartholine, and others, be answered: But I leave to Anatomists to consider what is to be said to some Observations that seem to contradict those Anatomical Experiments already mention'd: Such was particularly that which I remember I have read in Sennertus (from the observation of his Father-in-law Schato) of a Melancholy Student, who having stabb'd himself, and pierced the Diaphragme in the thinner or tendonous part (call'd by many the Nervous Circle) lived seven Months after he had wounded himself, though after his death (preceded by violent Vomitings) the Wound (perchance dilated by those strainings) appear'd so great, that the whole Stomach was found to have got in by it into the left side of the Thorax. And such also was the accident that happen'd to a Noble Man, whom I remember I have seen, and who is yet alive, in whose Chest there hath, for these many years, remain'd a hole so great, that the motion of his Heart may be perceiv'd by it. These (I say) and some other Observations, I shall now forbear to insist on, because I hold it not unfit, before we come to consider the use of Respiration, that we acquaint Your Lordship with an Ingenious Conjecture, that was made at the cause of the hasty death of the Animals our Engine kill'd: namely, That it was not the want of Air that [Page] destroy'd them, but the Pressure of the innate Air in the cavity of the Chest; as if the spring of the Air being no longer counterballanc'd by the ambient Air, was thereby become so strong, that it kept the Thorax forcibly distended, and hinder'd its wonted contraction; and so compress'd the Lungs and their Vessels, as to obstruct the circulation of the Blood. And this Conjecture, as it is specious enough, so I might have admitted it for true; but that I consider'd, that (not to mention that one, especially of the Animals kill'd in our Engine, seemed manifestly for a pretty while, and not long before he dy'd, to move his Thorax, as if he exercis'd Respiration) the diligent Wallaeus relates, that he divers times observed, in the dissection of live Bodies, that the Membrane that invests the Lungs, had Pores in it as big as the larger sort of Peas, which agreeth with the Observations of Chyrurgions and Physicians, viz. That Matter collected in the Thorax, hath penetrated into the Lungs, and been discharged by coughing. And I remember too, that most of the Animals we kill'd in our Engine were Birds, of whose Lungs Harvey somewhere informs us, That he observ'd them very manifestly to open at their extremities into the Abdomen: And by such perforitions we may well'suppose the passage free betwixt the external Air, and that in the Abdomen: But this Conjecture may be farther consider'd. Besides, to show that the Animals that died in our Glasses, need not be supposed to have been kill'd by the want of Air, we foresee another Argument that we must deal so ingeniously with Your Lordship, as not to conceal. You very well know, that besides the generality of the Schools, there are many new Philosophers who, though they dissent from the old Peripateticks in other things, do, as they, deny the possibility of a Vacuum; and hold, that those spaces which are devoid of Air, and other grosser Bodies, are all of them exactly replenished with a certain Etherial Matter, so thin and subtle, that it can freely permeate the Pores of the compactedst and closest Bodies, and ev'n of Glass it self. Now some of those Naturalists that are of this perswasion may object, That the Animals that died in our Receiver, did so, not so much for lack [Page] of Air, as by reason that the Air that was pump'd out was necessarily succeeded by an Etherial substance; which consisting of parts vehemently agitated, and so very small, as without resistance to pass in and out through the very Pores of Glass; it may well be supposed, that a considerable quantity of this restless and subtle Matter, meeting together in the Receiver, with the excessive heat of it, may be quickly able to destroy a little Animal, or at least, make the Air too intemperately hot to be fit for Respiration.

But though this be a Difficulty not so easily to be resolved without the assistance of our Engine, yet I suppose we have already answer'd the Objection by our 38th and 39th Experiments; which, though we made partly for other purposes, yet we premis'd them only to clear up the difficulty proposed.

Another suspicion we should have entertain'd concerning the death of our Animals, namely, That upon the sudden removal of the wonted pressure of the ambient Air, the warm blood of those Animals was brought to an Effervescence or Ebullition, or at least so vehemently expanded, as to disturb the circulation of the Blood, and so disorder the whole Oeconomy of the Body. (This (I say) I should have had some suspicion of) but that Animals of a hot Constitution are not the sole ones that cannot in our exhausted Engine exercise the Function of Life. But I must not now dwell upon matters of this nature, because I think it high time to proceed to the consideration of the principal subject of our Engine, namely, the use of Respiration; or rather, The use of the Air in Respiration. For whereas of the divers uses of it mentioned by Anatomists the most, such as the Production and Modulation of the Voice by the Elision of the Air, the Larynx, &c. the expulsion of Excrements by Coughing, the conveying in of Odours by Inspiration, and some others, rather convenient for the well being of an Animal, than absolutely necessary to his Life: Whereas (I say) the other uses are such as we have said, The great Hippocrates himself gives this notable Testimony to the use of the Air, as to Animals endow'd with Lungs: Mortalibus (saith he) hic (spiritus) tum vitae, tum morborum aegrotis causa [Page]est. Tantáque corporibus omnibus spiritûs inest necessitas, ut fiquidem aliis omnibus & cibis & potionibus, quis abstineat, duos tamen aut tres, vel plures dies possit vitam ducere: At si quis spiritus in corpus vias intercipiat, vel exiguâ diei parte, homini pereundum fit; Adeo necessarius est usus spiritûs in corpore. Ad haec quoque, quum omnibus aliis actionibus homines quiescant, quod mutationibus innumeris vita sit exposita, ab hâc tamen solâ actione nunquam desistant animantia, quin aut spiritum adducant, aut reddant.

But touching the account upon which the Inspiration and Exspiration of Air (both which are comprehended in [...], Respiration) is so necessary to Life, both Naturalists and Physicians do so disagree, that it will be very difficult either to reconcile their Opinions, or determine their Controversies.

For first, Many there are who think the chief (if not sole) use of Respiration to be the cooling and tempering of that Heat in the Heart and Blood, which otherwise would be immoderate: And this Opinion, not only seems to be most received amongst Scholastick Writers, but divers of the new Philosophers, Cartesians, and others, admitted with some variation; teaching. That the Air is necessary, by its coldness, to condense the Blood that passeth out of the right Ventricle of the Heart into the Lungs, that thereby it may contain such a consistence, as is requisite to make it fit Fewel for the vital fire or flame, in the left Ventricle of the Heart. And this Opinion seems favour'd by this, That Fishes, and other cold Creatures, whose Hearts have but one cavity, are also unprovided of Lungs, and by some other considerations. But though it need not be deny'd, that the inspir'd Air may sometimes be of use by refrigerating the Heart; yet (against the Opinion that makes this Refrigeration, the most genuine and constant use of the Air) it may be Objected, That divers cold Creatures (some of which, as particularly Frogs, live in the Water) have yet need of Respiration, which seems not likely to be needed for Refrigeration by them that are destitute of any sensible heat, and besides, live in the cold Water: That even decrepid old Men, whose natural Heat is [Page] made very languid, and almost extinguish'd by reason of Age, have yet a necessity of frequent Respiration: That a temperate Air is fittest for the generality of breathing Creatures; and as an Air too hot, so also an Air too cold, may be inconvenient for them (especially, if they be troubled with an immoderate degree of the same quality which is predominant in the Air:) That in some Diseases the natural heat is so weaken'd, that in case the use of Respiratic were to cool, it would be more hurtfull than beneficial to Breath; and the suspending of the Respiration, may supply the place of those very hot Medicines that are wont to be employ'd in such Distempers: That Nature might much better have given the Heart but a moderate heat, than such an excessive one, as needs to be perpetually cool'd, to keep it from growing destructive; which the gentle, and not the burning heat of an Animal's Heart,. seems not intense enough so indispensably to require. These, and other Objections, might be oppos'd, and press'd against the recited Opinion: But we shall not insist on them, but only add to them, That it appears not by our foregoing Experiments (I mean the 38th and 39th) that in our exhausted Receiver, where yet Animals die so suddenly for want of Respiration, the ambient Body is sensibly hotter than the common Air.

Other Learned Men there are, who will have the very substance of the Air to get in by the Vessels of the Lungs, to the left Ventricle of the Heart, not only to temper its heat, but to provide for the generation of Spirits. And these alledge for themselves the authority of the Ancients, among whom Hippocrates seems manifestly to favour their Opinion; and both Aristotle and Galen do sometimes (for methinks they speak doubtfully enough) appear inclineable to it. But for ought ever I could see in Dissections, it is very difficult to make out, how the Air is convey'd into the left Ventricle of the Heart, especially the Systole and Diastole of the Heart and Lungs being very far from being Synchronical: Besides, that the Spirits seeming to be but the most subtle and unctuous Particles of the Blood, appear to be of a very differing Nature from that of the lean and incombustible [Page] Corpuscles of Air. Other Objections against this Opinion have been proposed, and press'd by that excellent Anatomist, and my Industrious Friend, Dr. Highmore, to whom I shall therefore refer you.

Another Opinion there is touching Respiration, which makes the genuine use of it to be Ventilation not of the Heart, but of the Blood, in its passage through the Lungs; in which passage, it is dis-burthened of those Excrementitious Steams proceeding, for the most part, from the superfluous Serosities, of the Blood, (we may add) and of the Chyle too, which (by those new Conduits of late very happily detected by the Famous Pecquet) hath been newly mix'd with it in the Heart.) And this Opinion is that of the Industrious Maebius, and is said to have been that of that excellent Philosopher Gassendus; and hath been in part an Opinion almost vulgar: But this Hypothesis may be explicated two ways: For first, The necessity of the Air in Respiration, may be suppos'd to proceed from hence; That as a Flame cannot long burn in a narrow and close place, because the Fuliginous Steams it uncessantly throws out, cannot be long receiv'd into the ambient Body; which, after a while, growing too full of them to admit any more, stifles the flame: So that the vital Fire in the Heart requires an ambient Body, of a yielding nature, to receive into it the superfluous Serosities, and other Recrements of the Blood, whose seasonable Expulsion is requisite to depurate the Mass of Blood, and make it fit both to circulate, and to maintain the vital heat residing in the Heart. The other way of explicating the abovementioned Hypothesis, is, by supposing, that the Air doth not only, as a Receptacle, admit into its Pores the Excrementitious vapours of the Blood, when they are expell'd through the Wind-pipe, but doth also convey them out of the Lungs, in regard that the inspired Air, reaching to all the ends of the Aspera Ateria, doth there associate it self with the exhalations of the circulating Blood, and when 'tis exploded, carries them away with it self: as we see that Winds speedily dry up the surfaces of wet Bodies, not to say any thing of what we formerly [Page] observed touching our Liquor, whose fumes were strangely elevated upon the ingress of the Air.

Now of these two ways of Explicating the use of Respiration, our Engine affords us this Objection against the first; That upon the exsuction of the Air, the Animals die a great deal sooner than if it were left in the Vessel; though by that exsuction the ambient space is left much more free to receive the Steams that are either breathed out of the Lungs of the Animal, or discharg'd by insensible Transpiration through the Pores of his Skin.

But if the Hypothesis propos'd, be taken in the other sense, it seems congruous enough to that grand observation, which partly the Phaenomena of our Engine, and partly the relations of Travellers, have suggested to us: namely, That there is a certain consistence of Air requisite to Respiration; so that if it be too thick, and already over-charged with Vapours, it will be unfit to unite with, and carry off those of the Blood, as Water will dissolve, and associate to it self but a certain proportion of saline Corpuscles; and if it be too thin or rarefied, the number or size of the Aërial Particles is too small to be able to assume and carry off the halituous Excrements of the Blood, in such plenty as is requisite.

Now that Air too much thicken'd (and as it were clogg'd) with Steams, is unfit for Respiration, may appear by what is wont to happen in the Lead-Mines of Devonshire, (and for ought I know, in those too of other Countries, though I have seen Mines where no such thing was complain'd of) for I have been informed by more than one credible Person (and particularly by an Ingenious Man, that hath often, for curiosity, digg'd in those Mines, and been imploy'd about them) that there often riseth Damps, as retaining the Germane Word by which we call them) which doth so thicken the Air, that unless the Work-men speedily make signs to them that are above, they would (which also sometimes happens) be presently stifled for want of Breath, and though their Companions do make haste to draw them up, yet frequently, by that time they [Page] come to the free Air, they are, as it were in a swoon, and are a good while before they come to themselves again. And that this swooning seems not to proceed from any Arsenical or Poysonous Exhalation contain'd in the Damp, as from its overmuch condensing the Air, seems probable from hence; That the same Damps oftentimes leisurely extinguish the flames of their Candles or Lamps; and from hence also that it appears (by many Relations of Authentical Authors) that in those Cellars where great store of new Wine is set to work, Men have been suffocated by the too great plenty of the Steams exhaling from the Must, and too much thickning the Air: As may be gathered from the custom that is now used in some hot Countries, where those that have occasion to go into such Cellars, carry with them a quantity of well kindled Coals, which they hold near their Faces; whereby it comes to pass, that the Fire discussing the Fumes, and rarefying the Air, reduceth the ambient Body to a consistence fit for Respiration.

We will add (by way of Confirmation) the following Experiment: In such a small Receiver, as those wherein we kill'd divers Birds, we carefully clos'd up one, who, though for a quarter of an hour he seem'd not much prejudiced by the closeness of his Prison, afterwards be [...]n first to pant very vehemently, and keep his Bill very open, and then to appear very sick; and last of all, after some long and violent strainings, to cast up some little matter out of his Stomach: which he did several times, till growing so sick, that he stagger'd and gasp'd, as being just ready to die. We perceiv'd, that within about three quarters of an hour from the time that he was put in, he had so thickened and tainted the Air with the Steams of his Body, that it was become altogether unfit for the use of Respiration: Which he will not much wonder at, who hath taken notice in Sanctorius his Statica Medicina, how much that part of our Aliments, which goeth off by insensible Transpiration, exceeds in weight all the visible and grosser Excrements both solid and liquid.

That (on the other side) an Air too much dilated is not serviceable for the ends of Respiration, the hasty death of the [Page] Animal we kill'd in our exhausted Receiver, seems sufficiently to manifest. And it may not irrationally be doubted, whether or no, if a Man were rais'd to the very top of the Atmosphere, he would be able to live many minutes, and would not quickly dye for want of such Air as we are wont to breath here below. And that this Conjecture may not appear extravagant, I shall on this occasion subjoyn a memorable Relation that I have met with in the Learned Josephus Acosta, who tells us, That when he himself past the high Mountains of Peru, (which they call Pariacaca) to which, he says, That the Alps themselves seem'd to them but as ordinary Houses, in regard of high Towers, he and his Companions were surprised with such extreme Pangs of Straining and Vomiting, (not without casting up Blood too) and with so violent a Distemper, that he concludes he should undoubtedly have died, but that this lasted not above three or four hours, before they came into a more convenient and natural temperature of Air: To which our Learned Author adds an Inference, which being the principal thing I design'd in mentioning, the Narrative I shall set down in his own words: I therefore (says he) perswade my self, That the Element of the Air is there so subtle and delicate, as it is not proportionable with the breathing of Man, which req [...]es a more gross and temperate Air; and I believe it is the cause that doth so much alter the Stomach, and trouble all the Disposition. Thus far our Author, whose Words I mention, that we may ghess by what happens somewhat near the Confines of the Atmosphere (though probably far from the surface of it) what would happen beyond the Atmosphere. That, which some of those that treat of the height of Mountains, relate out of Aristotle, namely, That those that ascend to the top of the Mountain Olympus, could not keep themselves alive, without carrying with them wet Spunges, by whose assistance they could respire in that Air, otherwise too thin for Respiration: (That Relation (I say) concerning this Mountain) would much confirm what hath been newly recited out of Acosta, if we had sufficient reason to believe it: But I confess, I am very diffident of the truth of it; partly because [Page] cause when I pass'd the Alps, I took notice of no notable change betwixt the consistence of the Air at the top and the bottom of the Mountain; partly because in a punctual Relation made by an English Gentleman, of his ascension to the top of the Pike of Tenariff (which is by great odds higher than Olympus) I find no mention of any such difficulty of breathing; and partly also because the same Author tells us out of Aristotle, That upon the top of Olympus there is no motion of the Air, insomuch, that Letters traced upon the dust, have been, after many years, found legible and not discompos'd; whereas that Inquisitive Busbequius (who was Embassadour from the German to the Turkish Emperour) in one of his eloquent Epistles, Epist. 3. tells us, upon his own knowledge, That Olympus may be seen from Constantinople, blanch'd with perpetual Snow; which seems to argue, That the top of that, as well as of divers other tall Hills, is not above that Region of the Air wherein Meteors are formed. Though otherwise, in that memorable Narrative which David Fraelichius, made of his ascent to the top of the prodigiously high Fraelichius' apud Varen. Geogra. Gener. lib. 1. cap. 19. Hungarian Mountain Carpathus: He tells us, That when, having pass'd through very thick Clouds, he came to the very top of the Hill, he found the Air so calm and subtle, that not a hair of his head mov'd, whereas in the lower Stages of the Mountain he felt a vehement Wind. But this might well be casual, as was his, having a clear Air where he was, though there were Clouds, not only beneath him, but above him.

But (though what hath been hitherto discours'd, incline us to look upon the Ventilation and Depuration of the Blood, as one of the principal and constant uses of Respiration; yet) methinks it may be suspected that the Air doth something more than barely help to carry off what is thrown out of the Blood in its passage through the Lungs, from the right Ventricle of the Heart to the left. For we see, in Phlegmatick Constitutions and Diseases, that the Blood will circulate tolerably well, notwithstanding its being excessively ferous: And in Asthmatical Persons, we often see, that though the Lungs [Page] be very much stuff'd with tough Phlegm, yet the Patient may live some Months, if not some Years. So that it seems scarce probable, that either the want of throwing out the supefluous Serum of the Blood for a few moments, or the detaining it, during so short a while, in the Lungs, should be able to kill a perfectly sound and lively Animal: I say, for a few moments, because, that having divers times try'd the Experiment of killing Birds in a small Receiver, we commonly found, that within half a minute of an hour; or thereabout, the Bird would be surpris'd by mortal Convulsions, and within about a minute more would be stark dead, beyond the recovery of the Air, though never so hastily let in. Which sort of Experiments seem so strange, that we were obliged to make it several times, which gain'd it the advantage of having Persons of differing Qualities, Professions and Sexes, (as not only Ladies and Lords, but Doctors and Mathematicians) to witness it. And to satisfie Your Lordship, that it was not the narrowness of the Vessel, but the sudden exsuction of the Air that dispatched these Creatures so soon; we will add, That we once inclos'd one of these Birds in one of these small Receivers, where, for a while, he was so little sensible of his Imprisonment, that he eat very chearfully certain seeds that we conveyed in with him, and not only lived ten minutes, but had probably lived much longer, had not a great Person, that was Spectator of some of these Experiments, rescu'd him from the prosecution of the Trial. Another Bird being within about half a minute, cast into violent Convulsions, and reduced into a sprawling condition, upon the exsuction of the Air, by the pity of some fair Lady's related to Your Lordship) who made me hastily let in some Air at the Stop-cock, the gasping Animal was presently recovered, and in a condition to enjoy the benefit of the Lady's compassion. And another time also, being resolved not to be interrupted in our Experiment, we did, at night, shut up a Bird in one of our small Receivers, and observ'd that for a good while he so little felt thealteration of the Air, that he fell asleep with his Head under his Wing; and though he afterwards awak'd sick, yet he continu'd [Page] upon his legs between forty minutes and three quarters of an hour; after which, seeming ready to expire; we took him out, and soon found him able to make use of the liberty we gave him for a compensation of his sufferings.

If to the foregoing Instances of the sudden destruction of Animals, by the removal of the ambient Air, we should now annex some, that we think fitter to reserve till anon; perhaps Your Lordship would suspect, with me, that there is some use of the Air which we do not yet so well understand, that makes it so continually needfull to the Life of Animals, Paracelsus indeed tells us, That as the Stomach concocts Meat, and makes part of it usefull to the Body, rejecting the other part, so the Lungs consume part of the Air, and proscribe the rest. So that according to our Hermetick Philosopher (as his followers would have him stil'd) it seems we may suppose that there is in the Air a little vital Quintessence (if I may so call it) which serves to the refreshment and restauration of our vital Spirits, for which use the grosser and incomparably greater part of the Air being unserviceable, it need not seem strange that an Animal stands in need of almost incessantly drawing in fresh Air. But though this Opinion is not (as some of the same Author) absur'd, yet besides that, it should not be barely asserted, but explicated and prov'd; and besides that, some Objections may be fram'd against it, out of what hath been already argu'd against the Transmutation of Air into vital Spirits: Besides these things, it seems not probable, that the bare want of the Generation of the wonted quantity of vital Spirits, for less than one minute, should within that time be able to kill a lively Animal, without the help of any external violence at all.

But yet, on occasion of this Opinion of Paracelsus, perhaps it will not be impertinent, if before I proceed, I acquaint Your Lordship with a Conceit of that deservedly Famous Mechanician and Chymist, Cornelius Drebell, who among other strange things that he perform'd, is affirmed (by more than a few credible Persons) to have contrived for the late Learned King James, a Vessel to go under Water; of which, trial was made in the Thames, [Page] with admired success, the Vessel carrying twelve Rowers, besides Passengers; one of which is yet alive, and related it to an excellent Mathematician that inform'd me of it. Now that for which I mention this Story, is, That having had the curiosity and opportunity to make particular enquiries among the Relations of Drebell, and especially of an Ingenious Physician that married his Daughter, concerning the grounds upon which he conceived it feasible to make men unaccustomed to continue so long under Water without suffocation, or (as the lately mention'd Person that went in the Vessel affirms) without inconvenience. I was answer'd that Drebell conceiv'd, that 'tis not the whole body of the Air, but a certain Quintessence (as Chymists speak) or spirituous part of it, that makes it fit for Respiration, which being spent, the remaining grosser body, or carcase (if I may so call it) of the Air, is unable to cherish the vital flame residing in the Heart: So that (for ought I could gather) besides the Mechanical contrivance of his Vessel he had a Chymical liquor, which he accounted the chief Secret of his submarine Navigation. For when from time to time he perceived, that the finer and purer part of the Air was consumed, or over-clogg'd by the Respiration, and steams of those that went in his Ship, he would, by unstopping a Vessel full of this Liquor, speedily restore to the troubled Air such a proportion of Vital parts, as would make it again for a good while fit for Respiration, whether by dissipating, or precipitating the grosser Exhalations, or by some other intelligible way, I must not now stay to examine, contenting my self to add, that having had the opportunity to doe some service to those of his Relations, that were most Intimate with him, and having made it my business to learn what this strange Liquor might be, they constantly affirm'd that Drebell would never disclose the Liquor unto any, nor so much as tell the matter whereof he had made it, to above one Person, who himself assured me what it was.

This account of Drebell's performance, I mention, not that I any farther assent to his opinion than I have already intimated, but because the Man, and the Invention being extraordinary, I [Page] suppose Your Lordship will not be displeas'd to know the utmost I could learn about it; especially not having found it mentioned by any Writer. Wherefore I have been sometimes inclin'd to favourable thoughts of their opinion, who would have the Air necessary to ventilate, and cherish the vital slame, which they do suppose to be continually burning in the Heart. For we see, that in our Engine the flame of a Lamp will last almost as little after the exsuction of the Air, as the life of an Animal: Nay, I remember, that though I devis'd a more promising way, to make a fire last in our exhausted Receiver, yet it would not succeed: We took a hard body made in the form of a Clove, but twice as long, and proportionably thick, this body being made of such a Composition, that if it be kindl'd at the upper end, it will most certainly burn away to the very bottom, much better than a Match; we convey'd it divers times kindl'd at the upper end, into one of our small Receivers, but still found, that though presently upon the exsuction of the Air, it would leave smoking, and seem quite gone out, and again begin to smoke as soon as the Air was let in upon it; yet if the Air were kept out but four or five minutes, the fire would be totally, and irrevocably extinguish'd. To which we will add, that though we convey'd into a great Receiver, a small lamp with rectifi'd spirit of Wine, that being so pure as not to smut the Cotten week, or so much as a piece of white Paper held over it; yet we could not by divers trials make the flame last a couple of minutes after the Air was begun to be drawn out. But though our Engine thus shews us a new kind of resemblance betwixt Fire and Life: Yet the opinion we have last mentioned is not free from Difficulties. For, though in the hearts of many Animals, Blood be a warm liquor, and in some even a hot one; yet it is not easie to conceive either how the Air (in substance) can get thither, or how, in case it could, it were able to increase the heat. Since, however, the Air may encrease the heat of a Coal by blowing off the ashes, and making the active Corpuscles pierce farther into the kindled body, and shatter it the more, yet we see hot Liquors have their heat allayed, [Page] and not augmented, by having Air blown on them. And whereas some Eminent Naturalists think it not inconvenient, to make the heat residing in the Heart to be a true flame, provided they add, that 'tis such a temperate, and almost insensible fire, as the flame of spirit of Wine, which will long burn upon fine white Linnen or Paper without consuming either: Give me leave to wish that they had been more curious to make differing trials with that liquor. For (as we observe in another Treatise) the reason why a Linnen cloth, dipped in common Spirit of Wine, is not burnt by the flame of it, is, because the Phlegm of the Liquor defends the Cloth: And the Flame of Spirit of Wine is so far from being too weak to burn a piece of Paper, or of Linnen, that I have us'd it in Lamps to distill Liquors out of tall Cucurbites, and found that the Spirit burned away indeed much faster than Sallet Oyl, but gave at least as great a heat: Nay, I have, for curiosity sake, melted crude Gold, and that readily enough, with the bare Flame of pure Spirit of Wine.

But not to press this any farther, we will, on this occasion, venture to subjoyn an odd Observation, which may perhaps invite to a farther Enquiry into the Opinion we have for Discourse sake oppos'd. Our English Democritus, Dr. Harvey, proposeth this difficult and noble Problem to Anatomists, Why a foetus, even out of the Womb, if involv'd in the secundines, may live a good while without Respiration; but in case after having once began to breath, its Respiration be stopp'd, it will presently die. We are far from pretending to solve so hard a Problem, but this we try'd in relation to it; We took a Bitch that was said to be almost ready to whelp, and having caused her to be hang'd, we presently open'd her Abdomen, and found four Puppeys in her Womb; one of these we took out, and having freed him from the Teguments that involved him, and from the Liquor he swam in, we observed that he quickly opened his Mouth very wide, moved his Tongue, and exercised Respiration; then we opened both his Abdomen and his Chest, and cut assunder the Diaphragme, notwithstanding which, he seemed often [Page] to endeavour Respiring, and mov'd in a notable manner, both the Inter costal Muscles, part of the Diaphragme, the Mouth and the Tongue: But that which we mention this Puppy for, was this, That being desirous to try whether the other young ones that had not yet breath'd at all, would long survive this or no; we took them also out of the Womb, and having open'd them found none of them so much alive, as to have any perceptible motion in his heart, whereas the heart of that Puppy which had once enjoy'd the benefit of Respiration, continued beating so long, that we our selves observ'd the Auricle to beat, after five or six hours; and a Servant that staid-up and watch'd it after we were gone to Bed, affirm'd, That he saw the Pulsation continue about two hours longer. I shall leave it to others to make Reflexions upon this Observation, compar'd with Dr. Harvey's Problem.

It is much doubted, whether Fishes breath under Water, and we shall not take upon us, as yet, to determine the Question either way, because we have not yet been able to procure little Fishes alive to make Experiments upon: That such as are not Setaceous (for such manifestly breath) have not Respiration, properly so called, such as is exercised by four footed Beasts, and Birds, may be argu'd from their having no cavity in their Hearts, and from their want of Lungs, whence they are observed to be Mute; unless we say, what is not altogether absurd, That their Gills seem somewhat Analogous (as to their use) to Lungs. But that on the other side, Air is necessary to the Lives even of Fishes, and that therefore 'tis probable they have some obscure kind of Respiration, seems manifest by two or three Observations and Experiments, mentioned by divers Authors, who tell us, That Fishes soon die in Ponds and Glasses quite fill'd with Water; if the one be so frozen over, and the other so closely stopp'd, that the Fishes cannot enjoy the benefit of the Air, if we allow them to be true. But because these Relations are not wont to be deliver'd by Writers upon their own Knowledge; as I shall not reject them, so I dare not build upon them, till I have opportunity to examine them by experience. [Page] In the mean time, we will add, That our Engine hath taught us two things that may illustrate the matter in hand: The one, That there is wont to lurk in Water, many little parcels of interspers'd Air, whereof it seems not impossible that Fishes may make some use, either by separating it, when they strain the Water thorow their Gills, or by some other way: The other, what may be collected from the following Experiment.

We took a large Eel, (being able to procure no other Fish alive) and removing it out of the vessel of Water, wherein it was brought us, into our great Receiver, we caus'd the Air to be pump'd out; and observ'd, That the Eel, after some motion to and fro in the Glass, seem'd somewhat discompos'd; and that when we had prosecuted the exsuction of the Air somewhat obstinately, she turn'd up her belly, as dying Fishes are wont to do, and from thence-forward lay altogether moveless, just as if she were stark dead; and though I did not think her so, yet the continuing in that posture, even after the Cover of the Receiver was taken off (whereby the Air was let in) I should have been of the opinion of the By-standers, if the Diffidence I am wont to exercise in trying Experiments (especially such as are not usual) had not invited me to take the Fish out of the Receiver, upon which she shew'd her self, by her vivid motions, as much alive as before.

But that is most strange which we observ'd of a great, gray, House-Snail (as they call it) which being clos'd up in one of our small Receivers, did not only not fall down from the side of the Glass, upon the drawing out of the Air. (For that may be ascrib'd to the tenacity of the Liquor wherewith Snails use to stick themselves, even to the smoothest Bodies) but was not so much as depriv'd of progressive motion by the recess of the Air: Though, except this Snail, we never put any living Creature into our Receiver, whom it did not kill, or at least reduce to seem ready to die. But as we shall not here examine what interest the glutinous, and uneasily dissipable nature of the Juices of Snails, may have on this event; so whether this escape of our Eel be ascrib'd to the particular and vivacious nature of this [Page] sort of Fishes; or to this, That the Air is not indeed necessary to the life of Fishes; or finally to this, That though these Animals need some Air, yet they need so little, that that which could not be drawn out of the Receiver, might (at least for a while) suffice them, we will not now determine.

Nor are we at leisure to examine that Paradox of Hippocrates, which some Learned Physicians have of late reviv'd, namely, That the Foetus respires in the Womb: For on the one side it seems very difficult to conceive, how Air should traverse the Body of the Mother, and the Teguments of the Child: And since Nature hath, in new-born Babes, contriv'd peculiar and Temporary Vessels, that the Blood may circulate thorow other Passages, than it is wont to doe in the same Individuals when they come to have the free use of their Lungs, it seems unlikely, that Infants in the Womb do properly respire: But then since our Experiments have manifested, That almost all kind of Liquors do, as well as Water, abound with interspers'd Corpuscles of Air, it seems not altogether absurd to say, That when the Foetus is grown big, he may (especially the upper part of the involving Amnios, being destitute of Liquor, and fill'd only with an halituous substance) exercise some obscure Respiration; especially, since 'tis not (as many wise Men think it) a Fable, That Children have been heard to cry in the Mothers Womb: For though it happens exceeding rarely, yet sometimes it hath been observ'd. And I know a young Lady, whose Friends, when she was some years since with Child, complain'd to me, that she was several times much frighted with the Cries of her Infant, which, till I disabus'd her, she and her Friends look'd upon as Portentous. And such Observations are the more credible, because not only Houswives, but more judicious Persons, mention it as no very unfrequent thing to hear the Chick pip and cry in the Egg, before the Shell be broken. But this I mention but as a probable, not a cogent Argument, till I can discover whether an Elision of an halituous Substance, though no true Air, may not at the top of the Larynx produce a Sound, since I find that the Blade of a Knife, held in several postures in [Page] the stream of Vapors (or rarefied Water) that issues out of an AEolipile, will afford various and very audible Sounds.

I had thoughts of conveying into our Receiver young ones, ripped out of the Womb of their Dams, with their involving Coats intire, but could not procure them And I have also had thoughts of trying whether it be not practicable, to make a Receiver, though not of Glass, yet with little Glass windows, so placed, that one may freely look into it, capacious enough to hold a Man, who may observe several things, both touching Respiration, and divers other matters; and who, in case of fainting, may, by giving a sign of his weakness, be immediately reliev'd, by having Air let in upon him. And it seems not impossible, but that by accustomance, some Men may bring themselves to support the want of Air a pretty while, since we see that divers will live, so much longer than other Men, under Water: that those that dive for Pearls in the West Indies are said to be able to stay a whole hour under Water. And Cardan tells us of one Colanus a Diver in Sicily, who was able to continue (if Cardan neither mistake nor impose upon us) three or four times as long. Not to mind Your Lordship, that You have Your self oftentimes seen in England, a corpulent Man, who is wont to descend to the bottom of the Thames, and bring out of deep holes at the bottom of the Banks, large Fishes alive in his hands. And Acosta tells us, he saw in Peru the like manner of fishing, but more difficult, practised by the Indians.

I made mention of some Men, and of Accustomance: because there are but very few, who, though they use themselves to it by degrees, are fit to support, for many minutes, the want of Air. Insomuch that an ingenious Man of my acquaintance, who is very famous for the usefull skill of drawing Goods, and even Ordnance, out of sunk Ships, being asked by me how long he was able to continue at the depth of 50 or 60 foot under Water, without the use of Respiration, confessed to me, that he cannot continue above two minutes of an hour, without resorting to the Air, which he carries down with him in a certain Engine (whereof I can show Your Lordship a description.) [Page] Another thing I also learn'd of him by enquiry, that was not despicable: For asking him, whether he found any use of chawing little Sponges, dipt in Oyl, in his mouth, when he was perfectly under Water, and at a distance from his Engine; he told me, that by the help of these Sponges he could much longer support the want of his wonted Respiration, than he was able to doe without them. The true cause of which, would perhaps, if discovered, teach us some thing pertinent to the Problem touching the Respiration of Fishes.

But the necessity of Air to the most part of Animals unaccustomed to the want of it, may best be judg'd of, by the following Experiments, which we try'd in our Engine, to discover, whether Insects themselves have not, either Respiration, or some other use of the Air equivalent thereunto.

We took then an humble Bee, one of those common flyes that are call'd Flesh-flies, and one of those hairy Worms that resemble Caterpillars, and are wont to be call'd Palmer-worms: These three we convey'd into one of our small Receivers, and observ'd, to the great wonder of the Beholders, that not only the Bee, and the Fly fell down, and lay with their Bellies upwards; but the Worm it self seem'd to be suddenly struck dead: All of them being reduc'd to lie without motion, or any other discernable sign of life, within somewhat less (if we mistake not) than one minute of an hour: And this, notwithstanding the smallness of the Animals in proportion to the capacity of the Vessels: Which circumstance we the rather mention, because we found that the Vessel was not free from leaks. And to satisfie the Spectators, that't was the absence of the Air that caus'd this great and sudden change: We had no sooner re-admitted the Air at the Stop-cock, than all the three Insects began to shew signs of life, and by little and little to recover. But when we had again drawn out the Air, their motions presently ceased, and they fell down seemingly dead as before, continuing moveless, as long as, by continuing to pump, the vessel was kept exhausted. This invited us thankfully to reflect upon the wise goodness of the Creator, who by giving the Air a spring, hath [Page] made it so very difficult, as Men find it, to exclude a thing so necessary to Animals: And it gave us also occasion to suspect, that if Insects have no Lungs, nor any part analogous thereunto, the ambient Air afsects them, and relieves them at the Pores of their skin, it not being irrational to extend to these Creatures that of Hippocrates; who saith, That a living Body is throughout perspirable; or to use his expression, [...], dispos'd to admit and part with what is Spirituous: Which may be somewhat illustrated by what we have elsewhere noted, That the moister parts of the Air readily insinuate themselves into, and recede from the pores of the Beards of wild Oats, and those of divers other wild Plants; which almost continually wreath and unwreath themselves according to, even, the light variations of the temperature of the ambient Air.

This Circumstance of our Experiment we particularly took notice of, that when at any time, upon the ingress of the Air, the Bee began to recover, the first sign of Life she gave, was a vehemen panting, which appear'd near the Tail: Which we therefore mention, because we have observ'd the like in Bees drown'd in Water, when they first come to be reviv'd by a convenient heat: As if the Air were in the one case as proper to set the Spirits, and Alimental Juice moving, as heat is in the other; and this may, perchance, deserve a farther consideration.

We may add, That we scarce ever saw any thing that seem'd so much as this Experiment, to manifest, That even living Creatures (Man always excepted) are a kind of curious Engines, fram'd and contriv'd by nature (or rather the Author of it) much more skilfully than our gross Tools and imperfect Wits can reach to. For in our present Instance we see Animals, vivid and perfectly sound, depriv'd immediately of motion, and any discernable signs of life, and reduc'd to a condition that dissers from death, but in that it is not absolutely irrecoverable. This (I say) we see perform'd without any, so much as the least external violence offer'd to the Engine; unless it be such as is offered to a Wind-Mill, when the Wind ceasing to blow on the Sails, all the several parts remain moveless and useless, till a new Breath put them into motion again.

[Page]And this was farther very notable in this Experiment; That whereas 'tis known that Bees and Flies will not only walk, but flie for a great while, after their heads are off; and sometimes one half of the Body will, for divers hours, walk up and down, when it is sever'd from the other: Yet, upon the exsuction of the Air, not only the progressive motion of the whole Body, but the very motions of the Limbs do forthwith cease; as if the presence of the Air were more necessary to these Animals, than the presence of their own Heads.

But it seems, that in these Insects, that fluid Body (whether it be a Juice or Flame) wherein Life chiefly resides, is nothing neaŕ so easily dissipable, as in perfect Animals. For whereas we have above-recited, That the Birds we conveyed into our small Receiver were within two minutes brought to be past recovery, we were unable (though by trying him that pump'd) to kill our Insects by the exsuction of the Air: For though, as long as the Pump was kept moving, they continued immovable; yet when he desisted from pumping, the Air that press'd in at the unperceiv'd Leaks (did though slowly) restore them to the free exercise of functions of Life.

But, My Lord, I grow troublesome, and therefore shall pass on to other Experiments: Yet without despairing of your pardon for having entertain'd you so long about the use of Respiration, because it is a subject of that difficulty to be explain'd, and yet of that importance to humane Life, that I shall not regret the trouble my Experiments have cost me, if they be found in any degree serviceable to the purposes to which they were design'd. And though I despair not but that hereafter our Engine may furnish us with divers Phaenomena usefull to illustrate the Doctrine of Respiration; yet having not, as yet, had the opportunity to make the other trials, of various kinds, that I judge requisite for my Information: I must confess to Your Lordship, that in what I have hitherto said, I pretend not so much to establish, or over-throw this or that Hypothesis, as to lay together divers of the Particulars that occurr'd to me, in order to a future inquiry. I say, divers of the Particulars, because [Page] I could add many others, but that I want time, and fear that I shall need Your Lordship's pardon, for having been so prolix in writing; and that of Physicians (which perhaps I shall more easily obtain) for having invaded Anatomy, a Discipline which they challenge to themselves, and indeed have been the almost sole Improvers of. Without denying then that the inspir'd and exspir'd Air may be sometimes very usefull, by condensing and cooling the Blood that passeth through the Lungs; I hold that the depuration of the Blood in that passage, is not only one of the ordinary, but one of the principal uses of Respiration. But I am apt also to suspect, that the Air doth something else in Respiration, which hath not yet been sufficiently explain'd; and therefore, till I have examin'd the matter more deliberately, I shall not scruple to answer the Questions that may be asked me, touching the genuine use of Respiration, in the excellent Words employ'd by the acute St. Austin, to one that ask'd him hard Questions: Mallem quidem (says he) eorum quae à me quaesivisti, habere scientiam quam ignorantiam: sed quia id nondum potui, magis eligo cautam ignorantiam confiteri, quam falsam scientiam profiteri.

EXPERIMENT XLII.

HAving (partly upon the consideration of some of the foregoing Experiments, and partly upon grounds not now to be insisted on) entertain'd a suspicion, that the action of Corrosive Liquors in the dissolving of Bodies, may be considerably varied by the gravitation or pressure of the incumbent Air, and the removal of it; I thought fit to examine my Conjecture by the following Experiment.

I took whole pieces of red Coral, and cast them into as much spirit of Vineger, as sufficed to swim above an Inch over them: These substances I made choice of, that the Ebullition upon the Solution might not be too great, and that the operation might last the longer.

Having then put about half a score sprigs of Coral, together with the Menstruum, into a somewhat long neck'd Viol, whereof [Page] they seem'd scarce to fill a third part, we convey'd that Viol into one of our small Pneumatical Glasses, containing by ghess about a Quart of Water; and having fastned on the Cover, after the accustom'd manner, we suffered the Liquor to remain unmov'd a while, to observe whether the Menslruum would work upon the Coral otherwise than besore. But sinding there did only arise, as formerly, a pretty number of small Bubbles, that made there no sensible froth upon the surface of the distill'd Vineger, there were made two or three exsuctions of the Air; upon which, there emerg'd from the Coral such a multitude of Bubbles, as made the whole Body of the Menstruum appear white; and soon aster a Froth, as big as all the rest of the Liquor, was seen to swim upon it: And the Menstruum plainly appear'd to boil in the Glass, like a seething Pot. And though, if we desisted but one minute from pumping, the decrement of the Froth and Ebullition, upon the getting in of a little Air, at some leak or other, seem'd to argue, that the removal of the pressure of the external Air was the cause, or, at least, the occasion of this Effervescence: Yet to evince this the more clearly, we turn'd the Key, and let in the external Air at the Stop-cock; immediately upon whose entrance the Froth vanish'd, and so many of the Bubbles within the body of the Liquor disappear'd, that it lost its whiteness, and grew transparent again: The Menstruum also working as languidly upon the Coral, as it did before they were put into the Receiver: But when we had again drawn out the Air, first the whiteness re-appear'd, then the Ebullition was renew'd, which, (the pumping being a while longer and nimbly pursued,) grew so great, that for 3 or 4 times one aster another, when ever the Air was let out of the Receiver into the emptied Cylinder, the frothy liquor overflow'd the Glass, and ran down by the sides of it: And yet, upon the readmitting of the excluded Air, the boiling Liquor grew immediately as calm and as transparent as at first: As if indeed the operation of it, upon the Coral, had been facilitated by the exsuction of the incumbent Air, which on its recess, lest it more easie sor the more active parts of the liquor to shew themselves such, than it was [Page] whilst the wonted pressure of the Air continued unremoved. It may indeed be suspected, that those vast and numerous Bubbles proceeded, not from the action of the Menstruum upon the Coral, but from the suddain emersion of those many little parcels of Air that (as we formerly observ'd) are wont to be dispers'd in Liquors, without excluding Spirit of Vineger; but having had this suspicion before we try'd the Experiment, we convey'd our distill'd Vineger alone into the Receiver, and kept it a while there, to free it from its Bubbles (which were but very small) before ever we put the Coral into it. It may be suspected likewise, that the agitation of the Liquor, necessary following upon the shaking of the Glass, by pumping, might occasion the recited Ebullition; but upon trial made, there appear'd not any notable change in the Liquor, or its operation, though the containing Vessel were shaken, provided no Air were suck'd out of it. The former Experiment was another time try'd in another small Receiver, with Coral grosly powdred, and the success was very much alike, scarce differing in any thing, but that the Coral being reduc'd to smaller parts, upon the ebullition of the Liquor, so many little lumps of Coral would be carried and Boy'd up by the emerging Bubbles, as sometimes to darken the Viol, though the same Coraline Corpuscles would be let fall again upon the letting in of the Air.

Some thing also we try'd in our great Receiver, concerning the solution of Metals in Aqua fortis, and other Corrosive Liquors; but partly the stink, and partly some accidents, kept us from observing any thing peculiar and remarkable about those Solutions.

One thing we must not omit, that when the Spirit of Vineger was boiling upon the Coral, we took off the Cover of the Receiver, and took out the Viol, but could not find, that notwithstanding so very late an Ebullition, the Liquor had any heat great enough to be at all sensible to our hands.

EXPERIMENT XLIII.

WE will now subjoyn an Experiment, which, if the former did not lessen, the wonder of it would probably appear [Page] very strange to Your Lordship, as it did to the first Spectators of it.

The Experiment was this: We caus'd Water to be boil'd a pretty while, that by the heat it might be freed from the latitant Air, so often already taken notice of in common Water: Then almost filling with it a Glass Viol, capable of containing near four Ounces of that Liquor; we convey'd it, whilst the Water was yet hot, into one of our small Receivers (big enough to hold about a pound of Water) and having luted on the Cover, we caus'd the Air to be drawn out: Upon the two first exsuctions, there scarce appear'd any change in the Liquor, nor was there any notable alteration made by the third; but at the fourth, and afterwards, the Water appear'd to boil in the Viol, as if it had stood over a very quick Fire; for the Bubbles were much greater than are usually found upon the Ebullition of very much more Water than was contain'd in our Viol. And this Effervescence was so great in the upper part of the Water, that the Liquor boyling over the top of the Neck, a pretty deal of it ran down into the Receiver, and sometimes continued (though more languidly) boyling there. Prosecuting this Experiment, we observ'd, that sometimes, after the first Ebullition, we were reduc'd to make divers exsuctions of the Air, before the Liquor would be brought to boil again. But at other times, as often as the Key was turn'd to let the Air pass from the Receiver into the Pump, the Effervescence would begin afresh, though the Pump were ply'd for a pretty while together; which seem'd to argue, that the boyling of the Water proceeded from hence, That upon the withdrawing the pressure of the incumbent Air, either the fiery Corpuscles, or rather the Vapors agitated by the heat in the Water (which last, what we have formerly noted touching the raresied Water of an AEolipile, manifest to be capable of an Elastical Power) were permitted to expand themselves mightily in the evacuated Receiver; and did, in their tumultuous Dilatation, list up (as the Air is wont to do) the uppermost part of the Water, and turning it into Bubbles, made the Water appear boiling. This conjecture was farther confirm'd by these additional [Page] Circumstances: First, The Effervescence was confin'd to the upper part of the Water, the lower remaining quiet, unless the Liquor were but shallow. Next, although sometimes (as is already noted) the Ebullition began again, after it had ceas'd a pretty while, which seem'd to infer, That some concurrent cause (whatever that were) did a little modifie the operation of heat; yet, when the Water in the Viol could by no pumping be brought to boil any more, the self-same Water, being in the very same Viol warm'd again, and reconvey'd into the Pneumatical Glass, was quickly brought to boil afresh, and that vehemently and long enough; not to mention, that a new parcel, taken out of the same parcel of the boiled Water with the former, and put in cold, could by no pumping be brought to the least shew of Effervescence. Besides, having try'd the Experiment in hot Sallet Oyl, being a much more tenacious Liquor, and requiring a stronger heat to make it boil, could not be brought to an Effervescence in our Receiver; whereas the Chymical Oyl of Turpentine, being thinner and more volatile, was presently made to boil up, till it reach'd four or five times the former height in the Viol, in whose bottom it lay, and continued boiling till it was almost reduc'd to be but luke-warm. Wine also being a more thin and spirituous Liquor than Water, being convey'd in hot, instead of the Oyl, did, as I remember, at the very first exsuction begin to boil so vehemently, that, in a short time that the Pump was kept moving, four parts of five, by our ghess, boil'd over out of the Viol, though it had a pretty long Neck. On which occasion we will add, that even the Water it self, near one half, would sometimes boil over into the Receiver before it became luke-warm. And it was also remarkable, that once, when the Air had been drawn out, the Liquor did, upon a single Exsuction, boil so long with prodigiously vast Bubbles, that the Effervescence lasted almost as long as was requisite for the rehearsing of a Pater Noster. Now the Experiment having been try'd more than once, and found to succeed as to the main, seems much to countenance the Conjecture we made at the beginning of this Letter, where we told [Page] Your Lordship, That perhaps the pressure of the Air might have an interest in more Phaenomena than Men have hitherto thought. For as we had not then made this Experiment, so now we have made it, it seems to teach, That the Air, by its stronger or weaker pressure, may very much Modefie (as the School-men speak) divers of the Operations of that vehement and tumultuous Agitation of the small parts of Bodies, wherein the nature of heat seems chiefly, if not solely, to consist. Insomuch that if a heated Body were convey'd above the Atmosphere, 'tis probable that the heat may have a differing operation, as to the power of dissipating the parts of it, from what it hath here below.

To conclude, This Experiment might have been farther prosecuted, but our want of leisure makes us content our selves to add at present; That perhaps it would not be lost labour if this were try'd, not only with other Liquors, but with variety of heated, and especially soft or melted Bodies: But in such cases the Receiver ought to be shap'd, as is most proper to preserve the Cement where with the Cover must be fastned on, from being melted by the heat of the included Matter; the inconvenience to be hereby avoided, having befallen us in the use of a Receiver too shallow, though otherwise capacious enough.

The CONCLVSION.

BEing come thus far, My dear Lord, not without thoughts of proceeding farther: The unwelcome Importunity of my occasions becomes so prevalent, that it quite hinders, for the present, my design'd Progress; and reduceth me, not only to reserve for another opportunity that kind of Experiments, which, at some distance from the beginning of this Letter, I call'd (as Your Lordship may remember) Experiments of the second sort; but to leave unessay'd some of the first sort, which I might try in the Engine, as it now is, were it not that my Avocations are grown so urgent, for my remove from the place where the Engine was set up, that I am put to write Your Lordship this Excuse; Weary, and in an Inn which I take in my way to my Dearest Brother Corke: Who being at length arriv'd in England, after I have for [Page] divers years been deprived of his Company, and wish'd for it as long; what ever my other Occasions may be, my first Business must be to wait on Him and Your excellent Mother; in whose gratefull Company I may hope to forget a while those publick Calamities that distress this too unhappy Nation, Since that is indear'd to me, both by their personal Merit; by the near Relation which Nature gives me to Him, Affinity to Her, and Friendship to both; and also by their many Favours, especially that of my owing them My Lord of Dungarvan. But I suffer my self to be transported too far with these delightfull thoughts; To return therefore to our Engine. Though I find this Letter is beyond my expectation swell'd, not only into a Book, but almost into a Volume; yet the Experiments already mentioned in it, are so far from comprising all those that may be try'd by the help of our Engine, that I have not yet been able to try all those, which, presently occurring to my thoughts, upon my first seeing the working of it, I caus'd to be set down in a Catalogue within less than half an hour. But I doubt I have but too much cause to apprehend that the Affairs, and other things I complain of, have made it needfull for me to Apologize, as well for the things I have set down, as for those I am necessitated to omit. For as partial as Men use to be to the Children of their own Brains, as well as to those of their Loins, I must not deny that the foregoing Trials are not altogether free from such unaccuratenesses, nor the recital of them from such Imperfections, as I my self can now discern, and could, perhaps, partly mend, if I had the leisure to repeat the Experiments, with the Circumstances that have since offer'd themselves to my Thoughts, as things that might have been worth Observation or Enquiry. But the truth is, that I was reduc'd to make these Experiments, when my Thoughts had things that more concern'd me to imploy them, and the same avocations made me set them down, for the most part, as soon as I had made them, and in the same order, and that so fast, that I had not overfrequently the opportunity to mind any more than the bare Truth of what I set down; without allowing it any of those advantages that Method, Stile, and decent Embellishments, are [Page] wont to confer on the Composures they are imploy'd to adorn.

But, My Lord, though to invite and encourage You and Your learned Friends at Paris, to make a farther use of this Engine, than I have yet been able to doe, I am thus free to acknowledge the Imperfections of the foregoing Letter: Yet, if some Intelligent Persons mistake not, by what hath been done, such as it is, there is a way open'd, whereby Sagacious Wits will be assisted to make such farther Discoveries in some points of Natural Phylosophy, as are yet scarce dream'd of. And I am the more desirous to engage You to that Imployment, because I am apt to think, that if the making and writing of such Experiments shall cost You as much trouble as they have me, You will be inclin'd to excuse me; and if the Discoveries give You as much pleasure as they gave me, You will (perhaps) be invited to thank me. However, I think (My Lord) I may justly pretend, that the things I have set down have been faithfully Recorded, though not elaborately Written; and, I suppose, my former Papers may have long since satisfied You, that though many devise Experiments better than Your Servant, none perhaps hath related them more carefully and more truly: And particularly of These; sometimes one, sometimes another, hath been performed in the presence of Persons, divers of them eminent for their Writings, and all for their Learning. Wherefore, having in the foregoing Narratives made it my business to enoble them with the chief Requisites of Historical Composures, Candor, and Truth, I cannot despair that You will either excuse their Imperfections, or, at least, forgive them: Especially, considering that this unpolish'd Letter is as well a Production of Your Lordship's Commands and my Obedience, as a Testimony of my desire to make others beholden to My Lord of Dungarvan, by the same way which I indeavour to express my Self

Beconsfield, this 20th of December, 1659.

His Lordship's Most obedient Servant, and Most affectionate Uncle,

ROBERT BOTLE.

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A DEFENCE OF THE DOCTRINE Touching the Spring and Weight Of the AIR, Propos'd by Mr. R. BOYLE in his New Physico-Mechanical Experiments; Against the OBJECTIONS of FRANCISCVS LINVS.

Wherewith the Objector's FUNICULAR HYPOTHESIS is also Examin'd.

By the Author of those Experiments.

LONDON, Printed by M. Flesher, for Richard Davis Bookseller in Oxford, 1682.

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The Publisher TO THE READER.

Friendly Reader,

Yov may possibly in this Volume have expected the Appendix which the Author heretofore promised, and has intended shall contain some additional Experiments to those which were formerly publish'd, and are here now reprinted in this Second Edition. These following Answers to Franciscus Linus and Mr. Hobbs are presented in compensation of the delay, and for your forbearance of that Appendix, which ere long you may expect in kind. For the Author having hinted the Promise seems thereby to acknowledge the Debt, and to be content to continue the Obligation to see it performed. And these ought the rather to be his excuse, because the writing these Answers, and publishing the Sceptical Chymist, and some other Discourses, have been the principal hindrances to that Piece; which is really so near a readiness, that part of it has lain at the Press these six Months: But yet it being not all perfected, the Stationer was loth to delay any longer the Publication [Page] of these, for which he has been so frequently call'd upon. And they (though a Latine Edition is intended) appear now the rather in English, that they may accompany the Second Edition of the Original Experiments, which were printed first in that Language in Octavo; and that instead of the promised Appendix they may complete the bulk of the Quarto Volume.

As for that part of this Piece that concerns Mr. Hobbs, it might have been larger: but the information that the Author had that the Learned Dr. Wallis was writing against some passages in Mr. Hobbs his Dialogues (as well that concerning the Air as the rest) was the occasion why his H. would make no Animadversion on some passages therein, and thought it not fit to enlarge upon others. And for the Errata of the Press I hope they will not be many: However the Author as to these is to be excused, who never (in regard to his Eyes and Impediments on other occasions) gives himself the trouble of Corrections and Revises; neither could the Publisher much attend the Press, it being printed in a distant place from his usual Adobe. If, as I wish, you shall find this jealousie of mine to have been causless, you will have reason to give the Piece that is so kindly offered, and leads you such rare and untrodden paths in the best way of Natural Philosophy, the fairer entertainment and acceptance. Farewell.

Ro. Sh.

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THE AUTHOUR's PREFACE AND DECLARATION.

THEY that know how indispos'd I naturally am to Contentiousness, will, I presume, wonder to see me publickly engaged in two Controversies at once. But that I am still as averse as ever from entering into Disputes that may handsomly be declin'd, the way wherein I have managed the following Controversies will, I hope, evince. And the Inducements I now have to appear in publick are such, that it would be hard for me to resist the being prevail'd on by them.

For, in the first place, I was (by Name, as it were) challenged by a person, who undertook to disprove not one or two of my Conjectures, but as much of the whole Body of my Treatise as concern'd the Spring of the Air, which most of my Explications suppose. And this being done by a Learned Man, who writes very confidently of the goodness of his Hypothesis and Arguments, and his Book being soon after follow'd by another written by Mr. Hobbs, a man of Name in the World; there seem'd to be some danger that so early an Opposition might oppress the Doctrine I had propos'd, before it was well understood and duly ponder'd. Wherefore I fear'd I might be wanting to the Truth and my self, if I should at such a time be altogether silent; especially since I might probably divert many who would otherwise be forward to appear against us, by letting them see how defensible our Doctrine is even against such Adversaries as those I have reply'd to. And this course I the rather chose, that in case I should henceforward comply with those who would have me forbear to write any further of these [Page] Controversies, it might not be presently inferr'd from my silence, that a good Cause cannot enable a Pen no better than mine to defend it.

But I scarce doubt but that intelligent Readers, especially those that are imbued with the Principles of the Corpuscularian Philosophy, will be much more apt to think that I had reason to write the following Discourses, than to think that I had any to make them so prolix: And especially ingenious men, that are accustomed to admit nothing that either is not intelligible, or is precarious, will think divers of the Objections I reply to have needed no Answers, or at least no solemn ones. But to these I have four things to represent.

And First, That which not a little swells the bulk of the following Treatises, is the incerting those passages of my Adversaries that I examine in their own words: which being a Practice that I expect from any that shall think fit to animadvert upon any Opinion or Argument of mine; I thought it but equitable to do what I desir'd to have done to me, though oftentimes I could not do it in a little room.

Next, I was the more willing to prosecute some of Franciscus Linus his Objections, because the fear of being reduc'd to grant a Vacuum has so prevail'd with many eminent persons bred up in the received Philosophy of the Schools, that though they disagree both with him and among themselves about the particular manner of solving the Phaenomena of the Torricellian Experiment; yet they agree in ascribing them to some extremelyrarefi'd substance that fills up the space deserted by the Quicksilver. So that this Opinion, as to the main, being approved by many eminent Scholars, especially of that most learned Order of the Jesuites, (to whom perhaps its Congruity to some Articles of their Religion chiefly recommends it) I was willing to pay them that respect, as not to dissent from persons, divers of whom for their eminence in Mathematicks and other Learning I much esteem, without shewing that I do it not but upon Considerations that I think weighty.

Thirdly, though the Examiners Hypothesis have but few, [Page] and not very considerable, Arguments to countenance it; yet his Objections against our Doctrine (the Reply to which takes up the first Part of the following Treatise) are such, as though they may be solidly answered by any that throughly understands our Hypothesis, yet they may chance puzzle such Readers as do not, and these possibly will prove more than a few

And, Lastly, because that sometimes when the Argument objected did not perhaps deserve to be much insisted on, the Argument treated of deserv'd to be considered; I thought it not amiss to make use now and then of some such opportunities to illustrate the matter it self under consideration: Which I the rather did for these two Reasons;

First, because I find that, except by some able Mathematicians and very few other contemplative men, the Doctrine of the Spring of the Air, at least as I have proposed it, is not yet sufficiently apprehended, (and therefore needs to be inculcated.) Insomuch that through a great part of some late Discourses of men otherwise eminently learned, (written against other Elaterists, not me) there seems to run so great and clear a mistake, perhaps for want of skill in the Hydrostaticks, that I can scarce impute it to any thing, but to their not throughly understanding the Hypothesis they would confute.

And, Next, because I was willing to lay down in my Answer to the Objections I examin'd, the grounds of answering such other Arguments as may be built upon the same or the like Principles. And perhaps I may truly enough say, that in the following Treatise I have already in effect answered several discourses, written some before and some since mine, by learned men, about the Torricellian and other new Experiments relating to a Vacuum, though I forbore to mention the names or words of the Authors, because I found not that my Writings or Experiments were as yet known to them. To these things I may adde, that I thought the Discourses of Linus the fitter to be insisted on, because he seems to have more diligently than some others, (who yet venture to dispute against it) enquired into our Doctrine. And I shall not scruple to say thus much of an Adversary, [Page] (and one to whom I gave no provocation to be so) that though I dare not speak in general of those that have written either about the Weight of the Air, or else For or Against a Vacuum, because (as I acknowledge in the first Chapter following) I cannot yet procure the Books of divers learned men, especially of those great Personages, Robervall, Balianus and Casatus; yet among the Writers I have hitherto met with, who have recourse to the Aristotelean Rarefaction and Condensation in the Controversies under debate, scarce any seems to have contrived his Hypothesis better than our Linus. Not that I think his Principle is either true, or (at least to such as I) intelligible; but that the Funiculus he assumes being allow'd him, he may, for a Reason to be touch'd a little below, make out, though not all the Phaenomena of my Experiments, yet many more of them than most other Plenists, that deny the Spring of the Air, can deduce from their Hypotheses if granted. And in regard that, whereas we ascribe to the Air a Motion of Restitution outwards, he attributes to it the like Motion inwards, it cannot but happen that, though the Principles cannot both be true yet many of the Phaenomena may be explicable by which of them soever is granted: because of this, I say, it is not so easie as many ingenious Readers may be apt to think, to draw pertinent Objections from Experience against the Adversary I have to deal with. Which I represent, lest, as some may think I have employ'd more Arguments than I needed, so others should think I have omitted many; as indeed I have omitted some, that I might pertinently have employ'd.

But there is another sort of Persons besides those I mention'd at the beginning of this Preface, to whom I must address the remaining part of it; namely, to those who seem troubled, that I suffer my self to be diverted either by Linus or Mr. Hobbs from perfecting those Experimental About the History of Flame of Heat, of Colours, of the Origine of Qualities and Forms, &c. Treatises that are lying by me, almost promis'd by the learned Publisher of the Latine Edition of my Essays; and from prosecuting those wayes of enquiry into the Nature of things, [Page] wherein they are pleas'd to think I may be more serviceable to real Learning and the Lovers of it. And I confess that these Mens Reasons and Perswasions have so far prevailed with me, that after what I have done in the two following Treatises, to Vindicate my Writings from the Objections made against them by two Learned men of very differing Hypotheses, and thereby to shew in some measure that I am not altogether unacquainted with the way of defending oppos'd Truths, I have laid aside the thoughts of writing any more distinct or entire Polemical Treatises about the Subjects already disputed of. And to this I am invited by several other Reasons (besides what I have newly intimated.)

For first, as I elsewhere declare, it was not my cheif Design to establish Theories and Principles, but to devise Experiments, and to enrich the History of Nature with Observations faithfully made and deliver'd; that by these, and the like Contributions, made by others, men may in time be furnish'd with a sufficient stock of Experiments to ground Hypotheses and Theories on. And though in my Physico-Mechanical Epistle and my Specimens I have ventur'd some Conjectures also at the Causes of the Phaenomena I relate, lest the Discourse should appear to inquisitive Readers too jejune; yet (as I formerly said) I propos'd my Thoughts but as Conjectures design'd (though not onely, yet chiefly) to excite the Curiosity of the Ingenious, and afford some hints and assistance to the Disquisitions of the Speculative. And accordingly I have not forborn to mention divers things, which judicious Readers may easily perceive I foresaw that many would think unfavourable to the Opinions I inclin'd to. So that for me to leave Experimental for Controversial Studies, were a course unsuitable to the principal scope of my Writings.

Next, though I have adventur'd to improve the Doctrine of the Spring and Weight of the Air by some Supplements where I found it deficient, and to recommend it by some new Illustrations and Arguments deduc'd from my Experiments: yet the Hypotheses themselves (for the main) being the Opinions also of [Page] far learneder Men than I, it might be thought injurious both to them and to our common Cause, if I should needlesly go about to hinder them from the Honour of Vindicating the Truths we agree in; especially, some of them being Excellent Mathematicians, and others Eminent Naturalists, whose Concern to maintain the Hypotheses against Objections, if any shall arise, is equal to mine, and whose leisure and abilities far exceed those of a Person who both is sickly, and hath other employments enough, and who (if he were far better skil'd in Geometry than he pretends to be) hath such a weakness in his Eyes, as makes him both unwilling and unfit to engage in any Study where the conversing with Mathematical Schemes is necessary.

Thirdly, nor do I see much cause to doubt that the things I have deliver'd will notwithstanding my silence be left undefended: The forwardness I have already observ'd in divers Vertuosi to Vindicate those Writings, which they are pleas'd to say have convinc'd them, and to save me the labour of penning the following Treatises, scarce permitting me such an Apprehension. Especially since there are some things that will much facilitate their Task, if not keep men from putting them upon it. For though Mr. Hobbs and Linus have examin'd my Writings upon Principles wherein they differ as much from each other as from me; yet neither have they seen cause to deny any thing that I deliver as Experiment, nor have their Objections been considerable, whether as to Number or to Weight, against the Applications I have made of my Principles to solve the Phaenomena. So that usually without objecting any Incongruity to my particular Explications, they are fain to fall upon the Hypotheses themselves: in whose Defence I think I may with the more Reason expect to be seconded, because not onely I have endeavour'd, as I formerly noted, to lay the grounds of answering such Objections as I foresaw might arise; but I have also, to prevent or ease their labour, written the two first Parts of my Defence against Linus, without being oblig'd to do so for the Vindicating of my Explications, which are particularly maintain'd in the third Part.

I know not whether I may venture to adde on this occasion, [Page] That those who have taken notice of the usefulness of Experiments to true Philosophy, and have observ'd that nevertheless the Difficulty, Trouble, and Charge of making them is such, that even in this Learned Age of ours there are very few Bacon's or Mersennus's to be met with, and those who have either made themselves, or at least seen others make Experiments, even such as those I have publish'd, with the care I am wont to think my self oblig'd to employ on such Occasions; will perhaps not onely believe that they cost me far more time and pains than they that have not made nor seen such tryals are apt to imagine, but will possibly think it enough for a Person that is not by Profession a Scholar, to make them carefully, and set them down faithfully, and will allow him to let others Vindicate the Truths he may have the good fortune to discover, especially, when there are so many fitter for it than he, who have (as well as his Adversaries) more leisure to write Disputations than opportunity to prosecute Experiments; the latter of which to be perform'd as it ought to be, doth in many cases, besides some Dexterity scarce to be gain'd but by practice, require sometimes more Diligence, and oftentimes too more Cost, than most are willing, or than many are able, to bestow upon them.

To be short, though if any thing very worthy to be taken notice of by me be suggested against any of my cheif opinions or Explications, I may either take an occasion to say somewhat to it elsewhere, or at least have an opportunity to consider it in a Review, wherein I may alter, mend, supply, vindicate or retract divers Passages of my other Writings: yet I would not have it expected that I should exchange a Book with every one that is at leisure to write one against a Vacuum, or about the Air. Which Declaration I make, not that I think it will or ought to hinder any man from making use of his liberty to express a dissent, if he sees cause; but for these two Reasons.

The one, That my silence might not injure either the Truth or my self, by tempting men to think, that whatever I do not answer, I cannot; but might give unbiass'd and judicious Readers a Caution to allow as little of Advantage to the Writings of my [Page] adversaries upon the account of their being unanswer'd by me, as if I were no longer in the World. And the other, That I may not hinder those who would reply to such Adversaries by leaveing them an apprehension that either I may prevent them, or they me. To conclude, I see no cause to despair, that whether or no my Writings be protected, the Truths they hold forth will in time in spite of opposition establish themselves in the Minds of men, as the Circulation of the Bloud, and other formerly much contested Truths have already done. My Humour has naturally made me too careful not to offend those I dissent from, to make it necessary for any man to be my Adversary upon the account of Personal Injuries or Provocations. And as for any whom either Judgment or Envy may invite to contend, that the things I have communicated to the World deserved not so much Applause as they have had the luck to be entertain'd with; that shall make no Quarrel betwixt us: For perhaps I am my self as much of that mind as he; and however I shall not scruple to profess my self one of those who is more desirous to spend his time usefully, than to have the Glory of leaving nothing that was ever written against him unanswer'd; and who is more solicitous to pursue the wayes of discovering Truth, than to have it thought that he never was so much subject to Humane Frailties as to miss it.

[Page]

A DEFENCE Of Mr. R. BOYLE's EXPLICATIONS of his Physico-Mechanical EXPERIMENTS, against FRANCISCUS LINUS.

The I. Part. Wherein the Adversaries Objections against the Elaterists are examined.

CHAP. I.

A Newly-published Treatise, De Corporum inseparabilitate, being brought to my Hands, I find several Chapters of it employ'd to oppose the Explications I ventur'd to give of some of my new Experiments touching the Spring of the Air. Wherefore though I am very little delighted to be engag'd in Controversies, and though I be not at present without Employments enough (of a private, and of a publick Nature) to make it unseasonable for me, to be by a Work of this sort diverted from them; yet for the Reasons specified in the Preface, I hold it not amiss to examine briefly what is objected against the thing I have delivered: and the rather, partly, because the learned Author, whoever he be (for 'tis the Title-Page of his Book that first acquainted me with the name of Franciscus Linus) having forborn provoking Language in his Objections, allowes me in answering them to comply with my [Page] Inclinations and Custom of exercising Civility, even where I most dissent in point of Judgment. Besides, the Author himself has somewhat facilitated my Reply to him, by directing me in the ninth Page to some Books and Passages that I had not, when I publisht my Epistle, either seen or taken notice of. As indeed there are besides some of these several other Discourses that treat of the Torrecellian Experiments, which though by the names of their Authors I guess to be learnedly written, I have not to this day had opportunity to peruse, my stay in the remoter part of Ireland (whither Philosophical Books were not, in that time of publick Confusion, brought) having kept me from hearing of divers of them, till they were all bought up. Which I here mention, to excuse my self if I have not taken notice of some things or passages to be met with in these Writings, which their Learned Authors or Inquisitive Readers might justly perhaps expect I should take some notice of, in case those Writings had fallen into my hands. But to digress no further.

'Tis true indeed, and it somewhat troubles me that it is so, that I can scarce promise my self to make my Adversary a Proselyte, since he without scruple assumes those very things as Principles, that to me seem almost as great Inconveniences as I would desire to shew any Opinion I dislike, to be liable unto. But since whatever Operation the following Discourse may have upon the Person that occasion'd it, I hope it may bring some satisfaction to those Philosophers who can as little as I understand the Aristotelean Rarefaction, and who will as well as I be backward to admit what they cannot understand; it shall suffice me to defend the Truths I have deliver'd, if I cannot be so happy as to convince my acute Adversary of them; and I shall not believe my labour lost, if this Discourse can contribute to the Establishment of some Notions in Philosophy that I think not inconsiderable in the minds of those whose clear Principles make me the most respect their Judgements, and for whose sakes I principally write.

Now though I be not in strictness oblig'd to defend any more than such of my own Explications as the Examiner has thought [Page] fit to question, and those Particulars which I have added by way of Improvement to the two Hypotheses of the Spring and Weight of the Air; yet that I may the more effectually prosecute what I lately intimated I aim at in this Writing, and may as well illustrate my Doctrine as defend it, I shall divide the ensuing Treatise into three Parts; whereof the first is design'd to answer my Adversaries Objections against our Principles; the second shall examine the Funicular Hypothesis he would substitute in their stead; and the third shall contain particular Replyes to what he alledges against some of my particular Explications.

CHAP. II.

ALthough our Author confesses in his second Chapter, that the Air has a Spring as well as a Weight, yet he resolutely denies that Spring to be near great enough to perform those things which his Adversaries (whom for brevities sake we will venture to call Elaterists) ascribe to it. And his whole fourth Chapter, as the Title declares, is imploy'd to prove that the Spring of the Air is unable in a close place to keep the Mercury suspended in the Torrecellian Experiment. The proof of this Assertion he sayes is easie: But alledges two or three Arguments for it, which I think will be more easily answer'd than his Assertion evinc'd.

In the First he sayes that those Experiments concerning the Adhesion of ones finger, &c. which he had mentioned in the foregoing Chapter, eodem modo se habent in loco clauso ac in aperto. But the answering of this we shall suspend till anon; partly, because it may then be more conveniently examin'd, and partly, because our Author seems not to build much upon it, his chief Argument being that which he proposes in these words, Cum tota vis hujus Elaterii pendeat à refutato jam aëris aequipondio cum digitis 29½ argenti vivi, it a ut nec plus, nec Page. 20. minus faciat hoc elaterium in loco occluso, quam fit per illud aequipondium in loco aperto; manifestum est, cum jam ostensum sit fictitium planè esse hujusmodi aequipondium, fictitium quoque esse tale elaterium. Wherefore since all the validity of his Objection [Page] against the Spring of the Air depends upon his former Chapter, wherein he thinks he has disprov'd the Weight of the Air; it will behove us to look back into the former Chapter, and examine the four Arguments which he there proposes. But I must crave leave to vary from his method, and consider the third in the first place, because the removal of that Objection will facilitate and shorten the answer to the rest. His Third Argument therefore is thus set down. Nam si Tubus viginti tantum digitorum (quo usi sumus in primo Argumento) non totus impleatur argento, ut prius, sed spacium aliquod inter Page 16. digitum superiorem & argentum relinquatur in quo sit solus aër; videbimus subtracto inferiore digito superiorem non solum deorsum trahi, ut prius, sed etiam argentum jam descendere, idque notabiliter, quantum nimirum extendi potest exiguailla aëris particula à tali pondere descendente. Unde st loco illius aëris ponatur aqua, aliusve liquor qui non tam facilè extenditur, descensus nullus erit.

Hinc, inquam, contra hanc sententiam formatur argumentum: nam st externus ille aër nequeat vel hos viginti digitos argenti à lapsu sustentare, uti jam vidimus, quomodo quaeso sustentabit 29½? Certè haec nullatenus reconciliari possunt.

But to this Argument, which he thinks so irreconcilable with his Adversaries Hypothesis he has himself furnisht them with an Answer in these words, Dices forte ideo argentum in hoc casu descendere, quia deorsum truditur ab aëre illo sese per suum Elaterium dilatante. Which Anfwer I think sufficient for the Objection, notwithstanding the two exceptions he takes at it.

For first, whereas he sayes, that sic deberet digitus potius à tubo repelli, quam eidem affigi, cum non minus sursum quam deorsum fiat bujusmodi dilatatio: He considers not, that though the endeavour of the included Air to expand it self be at first every way alike, yet the expansion it self in our case must necessarily be made downward, and not upward; because the Finger that stops the Tube being expos'd on the upper parts and the sides to the external Air, has the whole Weight and pressure of the Atmosphere upon it; and consequently cannot be thrust away [Page] but by a force capable to surmount that pressure: whereas on the lower side of the Included Air there is the Weight of the whole Mercurial Cylinder to assist the Spring of the Air, to surmount the Weight of the Atmosphere that gravitates upon the restagnant Mercury. So that the Air included and endeavouring to expand it self, finding no assistance to expand it self upward, and a considerable one to expand it self downward, it is very natural that it should expand it self that way whence it finds less resistance. As accordingly it will happen, till the Spring of the Air be so far debilitated by its Expansion, that its pressure, together with the weight of the Mercury that remains suspended, will but counter-balance, not overcome, the pressure of the outward Air upon the restagnant Mercury. And this explication may be confirm'd by this trial that I have purposely made, namely, that if in stead of Quicksilver you employ Water, and leave as before in the Tube an Inch of Air, and then inverting it, open it under Water, you will perceive the included Inch of Air not to dilate it self any thing near (for I need not here define the Proportion) half so far as it did when the Tube was almost fill'd with Mercury; because the Weight of so short a Cylinder of Water does but equal that of between an Inch and an Inch and an half onely of Quicksilver, and consequently the inward Air is far less assisted to dilate it self and surmount the pressure of the outward Air by the Cylinder of Water than by that of Mercury. And as for what our Author sayes, that if instead of Air, Water or some other Liquor be left at the top of the Tube, the Quicksilver will not descend: the Elaterists can readily solve that Phaenomenon, by saying that Water has either no Spring at all, or but an exceeding weak one; and so scarce presses but by its Weight, which in so short a Cylinder is inconsiderable. Now the same solution we have given of our Examiners Objection, gives us also an account why the Finger is so strongly fastned to the upper part of the Orifice of the Tube it stops; for the included Air being so far dilated that an Inch, for example, left at first in the upper Part of the Tube, reaches twice or thrice as far as it did before the descent of the Quicksilver, its spring must be proportionably [Page] weakned. And consequently that part of the Finger that is within the Tube will have much les pressure against it from the dilated Air within, than the upper part of the same Finger will have from the unrarefi'd Air without. By which means the Pulp of the Finger will be thrust in (which our Author is pleas'd to call suckt in) as we shall ere long have occasion to declare in our Answer to his second Argument.

And having said thus much to our Authors first exception against the solution he foresaw we would give of his third Argument; we have not much to say at present to this second. For whereas he sayes, Concipi non posse quomodo aër ille sic se dilatet, argentumque deorsum trudat, nisi occupando Pag. 17. majorem locum: Quod tamen hi Authores quam maxime refugiunt, asserentes rarefactionem non aliter fieri, quam per corpuscula aut vacuitates: I wish he had more clearly express'd himself, since as his words are couch'd I cannot easily guess what he means, and much less easily discern how they make an Argument against his Adversaries. For, sure he thinks them not so absurd, as to imagine that the Air can dilate it self, and thrust down the Mercury, without in some sense taking up more room than it did before: For the very word Dilatation, and the effect they ascribe to the included Air, clearly imply as much; so that I see not why he should say that they are so averse from granting the Air to take up more Place than before, especially since he takes notice in the former Chapter, that we compare the Expansion of the Air to that of compress'd Wooll; and since he here also annexes that we explicate Rarefaction either by Corpuscles or Vacuities. But this later Clause makes me suspect his meaning to be, that the Elaterists do not admit that the same Air may adequately fill more of Place at one time than at another; which I believe to be as true as that the self-same lock of compress'd Wooll has no more Hairs in it, nor does adequately fill more Place with them, when it is permitted to expand it self, than whilst it remain'd compress'd. But against this way of Rarefaction our Author here has not any Objection, unless it be intimated in these words, Concipi non potest: Which if it be, [Page] I shall need onely to mind him in this place, that whereas many of the chiefest Philosophers, both of Ancient and our own times, have profest they thought not the Aristotelean way of Rarefaction conceivable; and he acknowledges (as we shall see anon) that it is not clear; what the ablest of his Party (the modern Plenists) are wont to object against the way of Rarefaction he dislikes, is, that it is not true, not that it is not intelligible.

CHAP. III.

OUR Authors Second Objection (for so I reckon it) is thus propos'd by him. Si sumatur tubus utrinque apert us sed longior, puta digitorum 40. Argentoque impleatur, eique Pag. 15. digitus supernè applicatur ut prius, videbimus subtracto inferiore digito, argentum quidem descendere usque ad consuetam suam stationem; Digitum autem superiorem fortiter intra tubum trahi, eique firmissime, ut prius, adhaerere. Ex quo rursum evidenter concluditur, argentum, in sua statione constitutum, non ibidem sustentari ab externo aëre, sed à funiculo quodam interno suspendi, cujus superior extremitas, digito affixa, eum sic intra tubum trahit, eique affigit. But this Argument being much of the same nature with that drawn from his third Experiment, the Answer made to that and to his first may be easily apply'd, and will be sufficient for this also; especially because in our present case there is less Pressure against the Pulp of the Finger in the inside of the Tube than in the third Experiment (where some Air is inoluded, though much expanded and weakned;) the Pressure of the Atmosphere being in the present case kept off from it by the subjacent Mercury, whereas there is nothing of that Pressure abated against the other parts of the Finger that kept it off from the deserted Cavity of the Tube, save onely that from the Pulp that is contiguous to the Tube, there may be somewhat of that Pressure taken off by the Weight of the Glass it self. But as for that Part of the Finger which immediately covers the hole, whether or no there be any Spring in its own fibres, or other constituent substances, which finding no resistance in the place deserted by the Quicksilver, may contribute to its swelling (for that we will [Page] not now examine) he that has duly consider'd the account already given of this Intrusion of the Pulp into the Glass, will find no need of our Authors internal Funiculus, which to some seems more difficult to conceive, than any of the Phaenomena in Controversie is to be explain'd without it.

CHAP. IV.

BY what we have already said against our Examiners Third Argument, we may be assisted to answer his first, though he propose it as a very clear Demonstration; and though it be indeed the principal thing in his Book. Sumatur (sayes he) tubus brevior digitis 29½ puta digitorum 20. non tamen clausus altero extremo, (ut hactenus) sed utrinque apertus: Page 12. Hic Tubus, immerso ejus orificio Argento restagnanti, suppositoque digito, ne effluat Argentum Tubo infundendum, impleatur Argento vivo: alius (que) deinde digitus orificio quo (que) applicetur, illud (que) bene claudat. Quo facto, si subtrahatur inferior digitus, sentietur superior vehementer trahi ac sugi intra tubum, tam (que) pertinaciter ei (vel argento potius, ut postea) adhaerere, ut ipsum tubum cum toto argento incluso facilè elevet teneat (que) in vase pendulum.

Ex quo sane experimento clarissimè refellitur haec sententia: Cum enim, juxta eam, Argentum in tubo hujusmodi 20. tantum digitorum, sursum trudatur à praeponderante aëre externo: nunquam profecto per eam explicabitur, quomodo digitus ille sic trahatur deorsum, tubo (que) tam vehementer adhaereat; non enim à trudente sursum potest sic deorsum trahi.

Thus far our Authors objection, in answer whereunto I have divers things to represent, to shew, that a good account may be given of this Experiment in the Hypothesis of the Elaterists, which is sufficient to manifest how far the argument is from being so unanswerable as the proposer of it would perswade his Reader.

I deny then that the Finger is drawn downward, or made by suction to adhere to the Tube; but I explicate that which he calls the suction of the Finger, as I lately did in answer to his third Argument, as we shall more particularly see anon.

He sayes indeed, that the Air which thrust up the Quicksilver [Page] cannot so strongly draw down the Finger. As if the Air were not a fluid body, but a single and entire pillar of some solid matter. But to shorten our Reply to his Objections, the best way perhaps will be briefly to explicate the Phaenomenon thus:

When the Tube is fill'd with Quicksilver, the Finger that stops the upper Orifice is almost equally press'd above and at the sides by the contiguous Air; but when the lower Finger is remov'd, then the Cylinder of Mercury, which before gravitated upon the Finger, comes to gravitate upon the restagnant Mercury, and by its intervention to press against the outward Air: so that against those parts of the Finger that are contiguous to the Air there is all the wonted pressure of the outward Air; whereas against that Pulp that is contiguous to the Mercury there is not so much pressure as against the other parts of the Finger by two thirds. I say by two thirds, or thereabout, because the Mercurial Cylinder in this Experiment is suppos'd to be twenty Inches high; and if it were but a little more than thirty Inches high, (which is a third more) then the weight of the Quicksilver would take off not two thirds only, but the whole pressure of the outward Air, from the above-mentioned pulp of the Finger. For in that case the Quicksilver would quite desert it, and settle beneath it. Wherefore since it has appeared by our Answer to the Examiner's third Argument, That the pressure of the outward Air is taken off from the body that remains in the upper part of the Tube, according to the weight of the Liquor suspended in the Tube; and since in our Hypothesis the pressure of the outward Air is able to keep thirty Inches of Quicksilver, or two or three and thirty foot of Water, suspended in a Tube; it need be no great wonder, if a pressure of the ambient Air, equal to the weight of a Cylinder of Water of near twenty two foot long, should be able to thrust in the pulp of the Finger at the upper Orifice of the Tube, and make it stick closely enough to the lip of it.

I know the Examiner affirms, That no thrusting or pressure from without can ever effect such an adhesion of the Finger to the Tube. But this should be as well prov'd as said. But, first, [Page] though I am willing to think the Examiner would not knowingly relate any thing he is not persuaded of; yet as far as I and another person very well vers'd in these Experiments have purposely tried, I could not find the Adhesion of the Finger to the Tube to be near so strong as our Author hath related. Secondly, if you carefully endeavour by pressure and otherwise to thrust the pulp of your Finger into the Orifice of the Tube, you may through the Glass perceive it to be manifestly tumid in the cavity of the Pipe. And if by pressing your Finger against the Orifice of the Tube, you should not make the pulp adhere quite so strongly to the Tube, nor swell quite so much within it, as may happen in some Mercurial Experiments; it is to be consider'd, that the Air being a fluid as well as a heavy body, it does not (as grosser Weights would) press only against the upper part of the Finger, but pressing as much of the finger as is expos'd to it almost every where, and almost uniformly, as well as strongly, it does by its lateral pressure on every side thrust in the Pulp of the Finger into the hole where there is not any resistance at all, or at least near so much pressure against the Pulp as that of the ambient Air against the parts of the Finger contiguous to it.

By this it may appear that we need not borrow the Objection our Author offers to lend us; namely, that in the Experiment under consideration the Quicksilver is press'd downward by the Spring of some Air lurking betwixt it and the Finger. (Though I am prone to think that unless the Experiment be made with a great deal of care, such a thing may easily happen, and contribute to the stronger Adhesion of the Finger to the Tube.) This I say may appear not withstanding what our Author Objects, that the Air expanding it self will thrust away the Finger upwards, since the contrary of that pretence we have lately manifested in the Answer to his Third Argument. And as for what he adds to confirm his Argumentation in these words, Quod vel inde confirmatur, Quia cum praeponderans ille aër succedat (uti asseritur) loco sublati inferioris Page 14. digiti, id est, eodem modo nunc sustentet Argentum quo [Page]ante ab applicato digito inferiore sustentabatur; manifestum est, non debere, juxta hanc sententiam, magis deorsum trahi digitum superiorem post sublatam inferiorem quam ante. Cum itaque contrarium planè doceat experientia, satis liquet sententiam illam esse falsam. We must consider that the Tube being suppos'd perfectly full of Mercury, the Finger that stops the lower Orifice is wont to be kept strongly press'd against it, lest any of that ponderous Liquor should get out between the Tube and the Finger. So that although both the lower Finger do indeed keep up the Mercury in the Tube, and the pressure of the outward Air would do so too; yet there is this difference, that the pressure of the Atmosphere depending upon its Weight, cannot be intended and weakned as we please, as can that of the undermost Finger. And therefore whereas the Atmospherical Cylinder will not keep up a Cylinder of Quicksilver of above thirty Inches high, those that make the Torricellian Experiment do often, upon one occasion or other, keep up with the Finger a Mercurial Cylinder of perhaps forty or fifty Inches or far more: So that whereas in our case, before the removal of the undermost Finger, the Pulp of the uppermost must have about the same pressure against it where it is contiguous to the Mercury, as there is against the other part of the same Finger; after the removal of the undermost Finger, there is as much of the Atmospherical Pressure, if I may so speak, taken off from the newly mention'd Pulp as counter-balances a Cylinder of Quicksilver of twenty Inches long.

CHAP. V.

THe Examiners Fourth and last Experiment is thus propos'd. Quarto denique (says he) impugnatur: Quia ex eo sequeretur, Argentum vivum per similem Tubum è vasculo exugi posse eâdem prorsus facilitate quâ ex eodem exugeretur Pag. 18. aqua: quod tamen experientiae repugnat, quâ docemur aquam in os sugentis facillimè attrahi; quo tamen Argentum vivum ne toto quidem adhibito conatu perduci queat, imo vix ad Tubi medietatem.

[Page]Sequelam autem sic ostendo: Quia cum in hac sententia nihil aliud agendum sit quam hoc, ut per Tubum sic ascendat subject us Liquor, sive Aqua fuerit, sive Argentum, nisi ut sugendo sur sum trahatur aër Tubo inclusus, quo sic attracto ascendit illico subject us Liquor, protrusus nimirum ab externo aëre jam praeponderante (uti docet Pecquettus in dissertatione Anatomica pag. 63.) manifestum est, eadem planè facilitate exugendum sic Argentum vivum qua exugitur Aqua: Quod quum Experientiae tam aperte repugnat, necesse est sententiam ex qua sequitur falsam esse.

This Experiment I remember I made some years ago, accordingly 'tis alledg'd in the fourth Essay of the Treatise (I was then writing) to prove against the Vulgar Opinion, that Liquors do not to prevent a Vacuum spontaneously ascend, which I presume will be so far allow'd of by our Author, who would have Liquors suppos'd to be rais'd by Suction violently drawn up by the contraction of his Funiculus. But to examine this Experiment, as it concerns the present Controversie, we may recal to mind that we formerly shew'd in the Answer to our Author's Third Argument, That when the Mercurial Cylinder that leans upon the restagnant Mercury has at the other end of it Air, kept from any entercourse with the Atmosphere, that included Air has so much of the Pressure of the external Air taken off from it as counterpoises the Mercurial Cylinder. And the Finger that is expos'd to the whole Pressure of the ambient Air in some of its Parts, and in others but to the much fainter Pressure of the included Air, endures an unusal Pressure from the preponderating power of the Atmosphere.

We may consider also that there is against the Thorax and those Muscles of the Abdomen that are subservient to Respiration the Pressure of the whole ambient Air. Which Pressure, notwithstanding, The Muscles design'd for the use of Respiration, are able without any considerable resistance to dilate the Thorax at pleasure; because, as fast as they open the Chest, and by dilating it weaken the Spring of that Air which is then [Page] within the Body, the external Air by flowing in, for want of finding the usual resistance there, keeps that within the Thorax in an AEquilibrium of force with that without. These things premised, 'tis not Difficult in our Hypothesis to give an Answer to our Examiner's Experiment. For we say when a Cylinder of Mercury is rais'd in the Tube to any considerable height, the Pressure of the Air in the Thorax is lessen'd by the whole weight of that Mercurial Cylinder, and consequently the Respiratory Muscles are thereby disabled to dilate the Chest as freely as they were wont, by reason of the prevalency of the undiminish'd Pressure of the external Air against the weakned Pressure of the internal: But if instead of Mercury you substitute Water, so short a Cylinder of that comparatively light Liquor takes off so little of the Pressure of the included Air, that it comes into the Lungs with almost its usual strength, and consequently with almost as much force as the outward Air presses with against the Thorax.

And on this occasion there occurs to my thoughts a noble Experiment of the most Ingenious Monsieur Paschal, which clearly shews, that if we could free the upper part of such a Tube as we are now considering from the Pressure of all internal Air, it would follow, as the Examiner says it should, that the Quicksilyer would by the Pressure of the outward Air be impell'd up into the Tube as well as Water, till it had attain'd a height great enough to make its Weight not inferiour but equal to that of the Atmosphere. The Experiment it self being so pertinent and considerable, we shall annex it in the same words wherein it is related by his Country-man and Acquaintance, the Learned and Candid Gassendus. Neque hoc verò solum, sed insuper vitreo Gass Phys. Sect. 1. Lib. 2. Pag. 204. De nupero Inanis Experimento. Diabete Clysteréve ea qua par fuerit longitudine confecto, & post embolum ad orificium us (que) compulsum, immisso ad normam in subjectum Hydrargyrum, deprehendit, ubi embolum sensim deinde educitur, consequi Hydrargvrum ascendere (que) ad eandem us (que) duorum pedum & digitorum trium eum semisse altitudinem. To which he immediately subjoyns a [Page] Circumstance very considerable to the present Controversie in the following Clause. Ac ubi deinceps, adhibita licet non majore vi, Embolum altius educitur, consistere Hydrargyrum, ne (que) amplius consequi, ac fieri interim Inane quod spatium intercipitur ab ipso ad Embolum usque. Thus far he. So that as to the Examiner's Experiment, we may well explicate it in our Hypothesis, by saying, that agreeably to it it happens, that in a more forcible Respiration the Mercurial Cylinder is raised higher than in a more languid; because, in the former Case, the Chest being more dilated, the included Air is also more expanded; whereby its debilitated Spring cannot as before enable the Mercurial Cylinder to counterpoise altogether the Pressure of the ambient Air. And that the reason why the Quicksilver is not by Respiration rais'd as high as it is kept suspended in the Torricellian Experiment, is not, that the Pressure of the outward Air is unable to raise it so high, but because, as we have already declar'd, the free Dilatation of the Thorax is opposed by the Pressure of the ambient Air; which Pressure being against so great a Superficies, and being but imperfectly resisted by the debilitated Pressure of the Air within the Thorax, will be easily imagined to be very considerable by him who considers that in our Engine, the Pressure of the external Air against the Sucker of less than three inches Diameter was, as we relate in the 33. Experiment, able to thrust up a Weight of above a hundred pound. And here we may observe upon the By in confirmation of our former Doctrine, that when we strongly suck up Quicksilver in a Glass Tube, though the Elevation of the Quicksilver be according to our Author performed likewise by his Funiculus contracting it self every way, and though there be a Communication betwixt the internal surface of the Lungs, and the cavity of the Tube; yet we feel not in our Lungs any endeavour of the shrinking Funiculus to tear off that Membrane they are lin'd with.

And thus we have examin'd our Author's four Arguments, to prove that in the Torricellian Experiment the Quicksilver cannot be kept suspended by the counterpoise of the external [Page] Air: Against which Opinion he tells us indeed, that other Arguments might be alledg'd) but as it is not probable that if he had thought them better than those he has Pag. 19. elected to insist on, he would have omitted them; so 'tis not unlikely that Answers might be as well found for them as for the others; especially since that which he singles out for a Specimen is, that from his Adversaries Hypothesis it would follow, that the Quicksilver would descend much more (I suppose 'tis a mistake of the Press, for much less) in cold Weather than in hot, because the Air is then thicker and heavier, and therefore ought to impel up the Quicksilver higher. For besides that we shall in its due place question the validity of our Author's Consequence; it will be here sufficient to Reply, that the Observation on which he grounds it does not constantly hold, as his Objection supposes: Which may appear by that part of our 18. Experiment whence the matter of fact is desum'd, as we shall have occasion to take further notice of when we shall come to the Defence of that Experiment. So that what has been hitherto Discours'd on both sides being duly consider'd, the Reader is left to judge what ground the Examiner had for the [...] wherewith he is pleas'd to conclude his Third Chapter, Maneat igitur tot Argumentis comprobatum, quorum quodlibet se solo sufficit, Argentum (facto Pag. 19. Experimento in loco aperto) per externi aëris gravitatem à lapsu minimè sustentari.

CHAP. VI.

HIs fourth Chapter, wherein the Title promises that he will prove, Argentum in loco occluso non sustentari à lapsu per ipsum aëris Elaterium, is very short, and does not require that we should dwell long upon it. For the proof he brings of his Assertion being this, Cumtota vis hujus Elaterii pendeat à refutato jam aëris aequipondio cum digitis 29½ Argenti Pag. 20. vivi, ita ut nec plus nec minus faciat hoc elaterium in loco occluso quam fit per illud aequipondium in loco aperto; manifestum est, cum jam ostensum sit fictitium planè esse hujusmodi aequipondium,[Page]fictitium quo (que) esse tale elaterium: This being no new Argument, but an Inference from those he had set down in the former Chapter, by our Answers to them it is become needless for us to make any distinct Reply to this. We shall rather desire the Reader to take notice, that whereas our Author says that according to his Adversaries, Nec plus nec minus faciat hoc Elaterium in loco occluso quam fit per illud AEquipondium in loco aperto; whatever others may have written, we for our part allow of this Opinion but in some Cases; for in others we have perform'd much more by the Spring of the Air, which we can within certain limits increase at pleasure, than can be perform'd by the bare weight, which for ought we know remains always somewhat near the same. And of this advantage that the spring of the Air may have in point of force above the weight of it, we have formerly given an Instance in our 17. Experiment, (where, by compressing the Air in the Receiver, we impell'd the Mercurial Cylinder higher than the station at which the counterpoise of the Air is wont to sustain it) and shall hereafter have occasion to give yet more considerable proofs. To the lately recited words our Examiner subjoyns these; Adde, cum allata jam capite praecedente experimenta de adhaesione digiti, &c. eodem modo se habent in loco Pag. 21. clauso ac in aperto, necessarium esse facta ex eis argumenta contra aequipondium, eadem quo (que) contra elaterium vim habere. But though he propose this as a new Argument, yet since 'tis built but upon the adhesion of the Finger (of which we have already given an account in our Hypothesis) I see not how it requires any new and particular Answer. And whereas he says, that the Experiments he had mentioned concerning the adhesion of ones Finger, &c. eodem modo se habent in loco clauso ac in aperto; I could wish he had added what way he took to make the Trials. For he gives no intimation that he did them any other ways than in ordinary rooms. And in such there scarce ever wants a communication betwixt the inward and outward Air, either at the Chimney, or Window, or Door not exactly shut, or at some hole or crevice or other, [Page] by means of which the weight of the Atmosphere has its operation within the room.

To his second Argument our Author adds not a third, unless we take that for an Argument which he immediately annexes to his last recited words: Et profectò (says he) si secum expenderent hi Authores, quanta sit difficultas explicandi Pag. 21. hujusmodi aëris elaterium, nisi idem aër se solo occupet majorem locum (ut paulo ante) credo eos sententiam facilè mutaturos. But this being said gratis, does not exact an Answer; and he must make it more intelligible than any man that I know of has yet done, how the same Air can adequately fill more space at one time than at another, before he perswade me to change my opinion about the Spring of the Air: Especially since he himself allows that the Air has a Spring, Pag. 11. whereby it is able, when it has been violently compress'd, to recover its due extension; the manner whereof if he will intelligibly explicate, his Adversaries will have no great difficulty to make out the spring of the Air. But whether his Hypothesis, or ours, be the more intelligible, will be more properly considered in the second part of our Discourse, to which we will therefore now proceed.

[Page]

The II. Part. Wherein the Adversaries Funicular Hypothesis is examin'd

CHAP. I. What is alledged to prove the Funiculus is consider'd; and some Difficulties are propos'd against the Hypothesis.

THE Hypothesis that the Examiner would, as a better, substitute in the place of ours, is, if I mistake it not, briefly this; That the things we ascribe to the weight or spring of the Air are really perform'd by neither, but by a certain Funiculus, or extremely thin substance, provided in such cases by Nature, ne detur vacuum, which being exceedingly rarefied by a forcible distension, does perpetually and strongly endeavour to contract it self into dimensions more agreeable to the nature of the distended body; and consequently does violently attract all the bodies whereunto it is contiguous, if they be not too heavy to be remov'd by it.

But this Hypothesis of our Authors does to me, I confess, appear liable to such Exceptions, that though I dislik'd that of his Adversaries yet I should not imbrace his, but rather wait till time and further Speculations or tryals should suggest some other Theory, fitter to be acquiesc'd in than this; which seems to be partly precarious, partly unintelligible, and partly insufficient, and besides needless: though it will not be so convenient to prove each of these apart, because divers of my Objections tend to prove the Doctrine, against which they are alledged, obnoxious to more than one of the imputed Imperfections.

First, then, the Arguments by which our Author endeavours to evince his Funiculus, are incompetent for that end. [Page] The Arguments which he proposes in his sixth Chapter, (where he undertakes to make good his Assertion) I there find to be three.

The first he sets down in these words, Constat hoc primò exjam dict is Capite praecedente: nequit enim argentum descendens sic digitum deorsum trahere, tubo (que) affigere, nisi Page 24. à tali Funiculo suspendatur, eum (que) suo pondere vehementer extendat, ut per se patet. But to this proof answer has been made already in the former Part of this Discourse: onely whereas the Author seems to refer us to the foregoing Chapter, we will look back to it, and take notice of what I find there against the Vacuists. For though I neither am bound, nor intend, in this Discourse to declare my self for, or against a Vacuum; yet since I am now writing against the Funicular Hypothesis, it will much conduce to shew that it is not firmly grounded, if I examine what he here alledges against the Assertors of a Vacuum.

In the next place therefore I consider that according to the Examiner, there can be no Vacuum; and that he makes to be the main reason why Nature in the Torricellian and our Experiments does act after so extraordinary a manner, as is requisite to the production of his Funiculus. For in the 47th. Page, having in his Adversaries name demanded what need there is at the descent of the Quicksilver, that before it falls a superficies should be separated from it, and extended; Respondeo (sayes he) ideo hoc fieri, ne detur vacuum; cum nihil aliud ibi adsit quod loco argenti descendentis possit succedere. To which he immediately subjoyns, (with what cogency I will not now examine) At (que) hinc plane confirmatur commune illud per tot jam elapsa secula usurpatum in Scholis axioma, viz. Naturam à vacuo abhorrere. And though he seem to make his Funiculus the immediate cause of the Phaenomena occurring in the Torricellian and our Experiments: yet that, if you pursue the inquiry a little higher, he resolves them into Natures abhorrency of a Vacuum, himself plainly informs us in the next page; Nam licet (sayes he) immediata ratio cur aqua v. g. ex hydria hortulana superne clausa (quo exemplo utuntur) non descendat, non sit metus va. ui,Pag. 48. [Page]sed ea quam modo diximus, nempe quod non detur sufficiens pondus ad solvendum illum nexum quo adhaereat aqua clausae hydriae summitati; ad eam tamen rationem tandem necessario veniendum est. But, though as well our Author's Funiculus, as the other scarce conceivable Hypotheses that learned men have devised, to account for the suspension of the Quicksilver otherwise than by the resistance of the external Air, seem to have been excogitated onely to shun the necessity of admitting a Vacuum: yet I see not how our Examiner cogently proves, either that there can be none in rerum naturâ, or that De facto there is none produc'd in these Experiments. For in his fifth Chapter (where he professedly undertakes that task) he has but these two incompetent Arguments. The first is drawn from the attraction, as he supposes, of the Finger into the deserted cavity of the Tube in the Torricellian Experiment: Quae quidem (sayes he) tam vehemens tractio & adhaesio, cum non nisi à reali aliquo corpore inter digitum & argentum Page. 22. constitutum queat provenire, manifestum est spatium illud vacuum non esse, sed verâ aliquâ substantiâ repletum. But to this Argument having already given an Answer, let us (without staying to urge, that the Vacuists will perhaps object, that they see not a Necessity, though they should admit of Traction in the case, that the internal substance must therefore perfectly replenish the deserted Cavity; without pressing this, I say, let us) consider his other, which he draws from the Diaphaneity of the deserted part of the Tube, which space (he sayes) were it empty, would appear like a little black Pillar, Eo quod nullae species visuales ne (que) ab eo ne (que) per illud possunt ad oculum pervenire. But (not to engage our selves in Optical Speculations and Controversies) if we grant him somewhat more than perhaps he can prove; yet as the Experiment will not demonstrate that there is nothing of body in any part of the space deserted by the Mercury, so neither will the Argument conclude (as the Proposer of it does twice in this Chapter) That space ver â aliquâ substantiâ repleri. For according to the Hypothesis of the Epicureans and other Atomists, who make Light to be a corporeal Effluvium [Page] from lucid bodies, and to consist of Atoms so minute, as freely to get in at the narrow Pores of Glass, there will be no cause to deny interspers'd Vacuities in the upper part of the Tube. For the Corpuscles of Light that permeate that space may be so numerous, as to leave no sensible part of it un-inlightned; and yet may have so many little empty Intervals betwixt them, that, if all that is corporeal in the space we speak of were united into one lump, it would not perhaps adequately fill the one half (not to say the tenth, or even the hundredth part) of the whole space: According to what we have noted in the 17. Experiment, that a Room my appear full of the smoke of a Perfume, though if all the Corpuscles that compose that smoke were re-united, they would again make up but a small Pastil. To which purpose I remember I have taken Camphire, of which a little will fill a Room with its odour, and having in well-clos'd distillatory Glasses caught the Fumes driven over by heat, I thereby reduc'd them to re-conjoyn into true Camphire, whose bulk is very inconsiderable in comparison of the space it fills as to sense, when the odorous Corpuscles are scattered through the free Air.

To which I might adde, that the Torricellian Experiment being made in a dark night, or in a Room perfectly darkn'd, if it succeed (as there is little cause to suspect it will not) it may well be doubted whether our Authors Argument will there take place. For if he endeavour to prove that the place in question was full in the dark, because upon the letting in of the Day, or the bringing in of a Candle, the light appears within it; the Vacuists may reply according to their Hypothesis, That that light is a new one, flowing from the lucid body that darts its corporeal beams quite through the Glass and Space we dispute about, which for want of such Corpuscles were not just before visible.

And supposing light not to be made by a trajection of Atoms through Diaphanous bodies, but a propagation of the impulse of lucid bodies through them; yet it will not thence necessarily follow, that the deserted part of the Tube must be full: As in our 27. Experiment (though many of those gross Aërial [Page] Particles that appear'd necessary to convey a languid sound were drawn out of our Receiver at the first and second Exsuction; yet there remain'd so many of the like Corpuscles, that those that were wanting were not miss'd by the sense, though afterwards, when a far greater number was drawn out, they were) so there may be matter enough remaining to transmit the impulse of light; though betwixt the Particles of that matter there should be store of vacuities intercepted. Whereas our Author pretends to prove, not onely that there is no coacervate Vacuity in the space so often mention'd, but absolutely that there is none. For 'tis in this last sense, as well as the other, that the Schools and our Author, who defends their Opinion, deny a V [...]cuum.

But notwithstanding what we have now discours'd, as in our 17. Experiment we declin'd determining whether there be a Vacuum or no; so now what we have said to the Examiners Argument, has not been to declare our whole sense of the Controversie, but onely to shew, that though his Hypothesis supposes there is no Vacuum, yet his Arguments do not sufficiently prove it: which may help to shew his Doctrine to be precarious; for otherwise the Cartesians, though Plenists, may plausibly enough (whether truly or no I now dispute not) decline the necessity of admitting a Vacuum in the deserted space of the Tube, by supposing it fill'd with their second and first Element, whose Particles they imagine to be minute enough freely to pass in and out through the Pores of Glass. But then they must allow the pressure of the outward Air to be the cause of the suspension of the Quicksilver: for though the materia caelestis may readily fill the spaces the Mercury deserts; yet that within the Tube cannot hinder so ponderous a liquor from subsiding as low as the restagnant Mercury; since all the parts of the Tube, as well the lowermost as the uppermost, being pervious to that subtile matter, it may with like facility succeed in whatever part of the Tube shall be forsaken by the Quicksilver.

The Examiners second Argument in the same place is, That since the Mercurial Cylinder is not sustain'd by the outward Air it must necessarily be, that it be kept suspended by his [Page] internal string. But since for the proof of this he is content to refer us to the third Chapter; our having already examin'd that, allows us to proceed to his third Argument, which is, That the Mercurial Cylinder, resting in its wonted station, does not gravitate: as may appear by applying the Finger to the immers'd or lower Orifice of the Tube. Whence he infers, that it must of necessity be suspended from within the Tube. And indeed if you dexterously apply your Finger to the open end of the Tube, when you have almost, but not quite, lifted it out of the restagnant Mercury, (which circumstance must not be neglected, though our Author have omitted it) that so you may shut up no more Quicksilver than the Mercurial Cylinder is wont to consist of, you will find the Experiment to succeed well enough: (Which makes me somewhat wonder to find it affirm'd, that the learned Maignan denies it) not but that you will feel upon your Finger a gravitation or pressure of the Glass-Tube, and the contained Mercury as of one body; but that you will not feel any sensible pressure of the Mercury apart, as if it endeavoured to thrust away your Finger from the Tube. But the reason of this is not hard to give in our Hypothesis; for according to that, the Mercurial Cylinder and the Air counterpoising one another, the Finger sustains not any sensibly-differing pressure from the ambient Air that presses against the Nail and fides of it, and from the included Quicksilver that presses against the Pulp. But if the Mercurial Cylinder should exceed the usual length, then the Finger would feel some pressure from that surplusage of Quicksilver, which the Air does not assist the Finger to sustain. So that this pleasant Phaenomenon may be as well solv'd in our Hypothesis, as in the Examiners: in which if we had time to clear an Objection, which we fore-see might be made, but might be answer'd too, we would demand why, when the Mercury included in the Tube is but of a due altitude, it should run out upon the removal of the Finger that stops it beneath, in case it be sustain'd onely by the internal Funiculus, and do, according to his Doctrine, when the Funiculus sustains it, emulate a solid body, [Page] if the pressure of the external Air has not (as our Author teaches it not to have) any thing to do in this matter.

And if some inquisitive person shall here object, That certainly the Finger must feel much pain by being squeez'd betwixt two such pressures, as that of a Pillar of thirty Inches of Quicksilver on the one side, and an equivalent pressure from the Atmospherical Pillar on the other, it may readily be represented, that in fluid bodies (such as are those concern'd in our Difficulty) a solid body has no such sense of pressure from the ambient bodies as (unless Experience had otherwise instructed us) we should perhaps imagine. For, not to mention that having inquired of a famous Diver, whether he found himself sensibly compressed by the Water at the bottom of the Sea; he agreed with the generality of Divers in the Negative: I am inform'd that the learned Maignan did purposely try, that his hand being thrust three or four Palmes deep into Quicksilver, his fingers were not sensible, either of any weight from the incumbent, or of any pressure from the ambient, Quicksilver. The reason of which (whether that inquisitive man have given it or no) is not necessary in our present Controversie to be lookt after.

To these three Arguments the Examiner addes not a fourth, unless he design to present it us in this concluding passage: Huc etiam faciunt insignes librationes quibus argentum subito descendens agitatur: Idem enim hic fit quod in aliis Pendulis Page 25. & ab alto demissis fieri solet. But of this Phaenomenon also tis easie to give an account in our Hypothesis by two several wayes; whereof the First (which is proper chiefly when the Experiment is made in a close place, as our Receiver) is, That the Quicksilver by its sudden descent acquires an impetus superadded to the pressure it has upon the score of its wonted gravity; whereby it for a while falls below its station, and thereby compresses the Air that leans upon the restagnant Mercury. Which Air by its own Spring again forcibly dilating it self to recover its former extension, and (as is usual in Springs) hastily flying open, expands it self beyond it, and thereby impells up [Page] the Quicksilver somewhat above its wonted station, in its fall from whence it again acquires somewhat (though not so much as before) of impetus or power, to force the Corpuscles of the Air to a Sub-ingression; and this reciprocation of pressure betwixt the Quicksilver and the outward Air decreasing by degrees, does at length wholly cease, when the Mercury has lost that superadded pressure, which it acquired by its falling from parts of the Tube higher than its due station. But this first way of Explicating these Vibrations is not necessary in the free Air: For if we consider the ambient Air onely as a weight, and remember what we have newly said of the impetus acquir'd by descent; this Phaenomenon may be easily enough explain'd, by taking notice of what happens in a Balance, when one of the equiponde rant Scales chancing to be depress'd, they do not till after many Vibrations settle in aequilibrio.

And on this occasion I shall adde this Experiment: I took a Glass Pipe, whose two legs (very unequal in length) were parallel enough, and both perpendicular to that part of the Pipe that connected them; (such a Syphon is describ'd in our 36. Experiment, to find the proportion of the gravity of Mercury and Water) into this Quicksilver was pour'd till 'twas some Inches high, and equally high in both legs: then the Pipe being inclin'd till the most part of the Quicksilver was fallen into one of the legs, I stopt the Orifice of the other leg with my Finger, and erecting again the Pipe, though the Quicksilver were forc'd to ascend a little in that stopt leg; yet by reason my Finger kept the Air from getting away, the Quicksilver was kept lower by a good deal in that stopt leg than in the other; but if by suddenly removing my Finger I gave passage to the included and somewhat comprest Air, the preponderant Quicksilver in the other leg would with the Mercury in this unstopt leg, make divers undulations before that liquor did in both legs come to rest in an aequilibrium. Of which the Reason may be easily deduc'd from what has been newly deliver'd; and yet in this case there is no pretence to be made of a Funiculus of violently distended Air to effect the Vibrations of the Mercury.

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CHAP. II Divers other Difficulties are objected against the Funicular Hypothesis

THirdly, But though our Examiner have not sufficiently proved his Hypothesis, yet perhaps it may be in its own nature so like to be true, as to deserve to be imbrac'd as such. Wherefore we will now take notice of some of those many things that to our apprehension render it very improbable.

And first, whereas our Author acknowledges that Quicksilver, Water, Wine, and other Liquors, will, as well one as another, descend in Tubes exactly sealed at the top, in case the Cylinder of liquor exceed the weight of a Mercurial Cylinder of 29½. Inches; and will subside no longer than till it is come to equiponderate a Cylinder of Quicksilver of that height; whereas, I say, the Examiner is by the ingenious Monsieur Paschall's, and other Experiments, induc'd to admit this; it cannot but seem strange that, whatever the liquor be, there should be just the same weight or strength to extend them into a Funiculus: though Water, for instance, and Quicksilver be near fourteen times as heavy one as the other, and be otherwise of very distant natures; and though divers other liquors, as Oyle and Water, be likewise of Textures very differing. And this may somewhat the more be wondred at, because our Author (in his Animadversions upon our 31. Experiment) is pleased to make so great a difference betwixt the disposition of bodies of various consistences, as fluid and firm, to be extenuated into a Funiculus, that he will not allow any humane force to be able to produce one, by the divulsion of two flat Marbles, in case the contact of their Surfaces were so exquisite as quite to exclude all Air; though in the same place his Ratiocination plainly enough teaches (which Experience however does) that adhering Marbles, though with extraordinary difficulty, may be forcibly sever'd, and according to him the superficial parts may be distended into a Funiculus, that prevents a Vacuum.

But now the Hypothesis of his Adversaries is not at all incumbred [Page] with this difficulty. For the weight of the outward Air being that which keeps liquors suspended in Tubes sealed at the top; it matters not of what nature or texture the suspended liquor is, provided its weight be the same with that of a Mercurial Cylinder equiponderant to the Aerial one: As if there be a pound of Lead in one Scale, it will not destroy the aequilibrium, whether what be put in the other be Gold, or Quicksilver, or Wooll, or Feathers, provided its weight be just a pound.

In the next place we may take notice, That the account our Examiner gives us of his Funiculus in the tenth Chapter, (where he takes upon him to Explicate it) is much more strange than satisfactory, and not made out by any such parallel operations of Nature, as his Adversaries will not (and may not well do it) dispute the truth of. Whereas the weight and Spring of the Air may be inferr'd from such unquestion'd Experiments as are nor concern'd in our present Controversie. For the gravity of the Air may be manifested by a pair of Scales, and the Spring of it discloses it self so clearly in wind guns and other Instruments, that our Adversary (as we have already had occasion to inculcate) does not deny it. But to consider his explication of his Funiculus, he would have us note two things: First, Argentum dum replet totum tubum, non mere tangere ejus summitatem (ut primo aspectu videtur) Pag. 38. sed eidem quo (que) firmiter adhaerere. Patet hoc (subjoyns he) experimento illo in primo argumento capitis tertii de tubo utrin (que) aperto. But what is to be answer'd to this proof may be easily gathered from what we have replyed to that Argument. And to what our Author addes to prove, That the adhesion of the Finger is to the subjacent Mercury, not to the Tube; namely, That Licet illud tubi orificium oleo, aliâve materiâ adhaesionem impediente, inungatur, non minus tamen firmiter Page. 38. adhaerebit digitus quàm priùs; an Answer may be drawn from the same place: nor perhaps will his reasoning much satisfie those who consider that bodies by trusion may easily enough be made stick together, as much as in our case the Tube [Page] and Finger do, notwithstanding one of them is anoynted with Oyle, and that this adhesion of the Finger to the Tube is to be met with in cases where the Surface of the included Quick-silver is not contiguous to the Finger, but many Inches below. As for what he addes concerning the reason why Water and Quicksilver ascend by suction, we have already taught what is to be answered to it, by ascribing that ascension to the pressure of the external Air: without any need of having recourse to a Funiculus; or imagining with him in this place, That because nothing besides the Water or Quicksilver can insuch cases succeed the Air, (which yet is not easie to be prov'd in reference to a thin AEthereal substance) therefore, Partes ipsius aëris (to use his expression) sic tubo inclusae (quae aliàs tam facile Pag. 40. separantur) nunc tam fortiter sibi invicem agglutinentur, ut validissimam (uti videmus) conficiunt catenam, qua non solum aqua, sed ponderosum illud argentum sic in altum trahatur. Which way of wreathing a little rarefied Air into so strong a rope, how probable it is, I will for a while leave the Reader to judge, and advance to our Author's second Notandum, which he thus proposes: Rarefactionem sive extensionem corporis ad occupandum majorem locum fieri non solo calore, sed etiam distensione Pag. 40, 41. seu vi divulsivâ: sicut è contra condensatio non solo frigore perficitur, sedetiam compressione, uti innumeŕa passim docent exempla. And 'tis true and obvious, that the condensation of bodies, taking that word in a large sense, may be made as well by compression as cold. But I wish he had more clearly exprest what he means in this place by that Rarefaction, which he sayes is to be made by distension, or a vis divulsiva, whereof he tells us there are innumerable instances. For, as far as may be gathered from the three Examples he subjoyns, 'tis onely the Air that is capable of being so extended as his Hypothesis requires Quicksilver and even Stones must be. And I know not how it will be proved, that even Air may be thus extended so far, as in the Magdeburg Experiment, to fill a place more than two thousand times as big as that it fill'd before. For that the [Page] same Air in this and his two foregoing Instances does adequately fill more space at one time than another, he proves but by the rushing in of water into the evacuated Glass, and filling it within a little quite full, which he sayes, is done by the distended Air that contracting it self draws up the water with it. Which Explication how much less likely it is, than that the water is in such cases impell'd up by the pressure of the Atmosphere, we shall anon (when we come to discuss his way of Rarefaction and condensation) have occasion to examine. In the mean time let us consider with him the Explication which, after having promis'd the two above recited Observations, he gives us of his Funiculus; Cum per primum Notandum argentum it a adhaereat tubi vertici, & per secundum, rarefactio Pag. 41. fiat per meram corporis distensionem, it a rem se habere, ut argentum descendens à vertice tubi affixam eirelinquat superficiem suam extimam sive supremam, eam (que) eous (que) suo pondere extendat extenuetque, donec facilius sit aliam superficiem similiter relinquere quam priorem illam ulterius extendere: Secundam igitur relinquit, eam (que) eodem modo descendendo extendit, donec facilius sit tertiam adhuc separari quam illam secundam extendere ulterius: & sic deinceps, donec tandem vires amplius non habeat superficies sic separandi & extendendi; nempe donec perveniat ad altitudinem digitorum duntaxat 29½. ubi quiescit, ut capite primo dictum est. Thus far our Examiners Explication: By which 'tis easie to discern, that he is fain to assign his Funiculus a way of being produc'd strange and unparallel'd enough. For, not to repeat our Animadversions upon the first of the two Notandum's, on which the Explication is grounded, I must demand by what force, upon the bare separation of the Quicksilver and the top of the Tube, the new body he mentions comes to be produc'd; or at least how it appears that the Mercury leaves any such thing as he speaks of behind it. For the sense perceives no such matter at the top of the Tube, nor is it necessary to explicate the Phaenomena as we have formerly seen. It may also be marvell'd at, that the bare weight of the descending Mercury should be able to extend a Surface into a Body. And besides, it seems [Page] precariously affirm'd, that there is such a successive leaving behind of one Surface after another as is here imagin'd: Nor does it at all appear how, though some of the Quicksilver were turn'd into a thin subtile substance, yet that substance comes to be contriv'd into a Funiculus of so strange a nature, that scarce any weight (for ought appears by his Doctrine) can be able to break it; that contrary to all other strings it may be stretched without being made more slender; and that it has other very odde properties, some of which we shall anon have occasion to mention. As for what our Author subjoyns in these words, Eodem ita (que) fere modo separari videntur hae superficies ab argento descendente, & in tenuissimum quendam funiculum Pag. 43, 44. per descendens pondus extendi, quo per calorem in accensa candela separantur hujusmodi superficies à subject a cera aut sevo, & in subtilissimam flammam extenuantur. Vbinotatu dignum, quemadmodum flamma illaplusquam millies sine dubio majus spatium occupat, quam antea occupaverat pars illa cerae ex qua conficitur; ita prorsus & hic existimandum Funiculum illum plusquam millies majus spatium occupare quàm prius occupaverat illa argenti particula ex qua sit exortus: Vti etiam sine dubio contingit, quando talis particula à subjecto igne in vaporem convertitur. Though it be the onely Example whereby he endeavours to illustrate the generation of his Funiculus, yet (I presume) he scarce expects we should think it an apposite one. For besides that there here intervenes a conspicuous and powerful Agent, namely, an actual Fire to sever and agitate the parts of the Candle; and besides that there is a manifest wasting of the Wax or Tallow turn'd into flame; besides these things, I say, we must not admit that the Fuel when turn'd into a flame does really fill (I say, not, with our Author) more than a thousand times, but so much as twice more of genuine space than the Wax 'twas made of. For it may be said that the flame is little or nothing else than an aggregate of those Corpuscles which before lay upon the upper superficies of the Candle, and by the violent heat were divided into minuter particles, vehemently agitated and brought from lying as it were upon a flat to beat off one another, [Page] and make up about the Wiek such a figure as is usual in the flame of Candles burning in the free Air. Nor will it necessarily follow, that the space which the flame seems to take up should contain neither Air nor AEther, nor any thing else, save the parts of that flame, because the eye cannot discern any other body there: For even the smoke ascending from the snuff of a newly-extinguish'd Candle appears a dark pillar, which to the eye at some distance seems to consist of smoke; when as yet there are so many Aerial and other invisible Corpuscles mingled with it, as if all those parts of smoke that make a great show in the Air were collected and contiguous, they would not perhaps amount to the bigness of a Pins head, as may appear by the great quantity of streams that in Chymical Vessels are wont to go to the making up of one drop of Spirit. And therefore it does not ill fall out for our turn, that the Examiner, to inforce his former Example, alledges the turning of a particle of Quicksilver into vapour, by putting fire under it: for if such be the Rarefaction of Mercury, 'tis not at all like to make such a Funiculus as he talks of, since those Mercurial Fumes appear by divers Experiments to be Mercury divided and thrown abroad into minute parts, whereby though the body obtain more of Surface than it had before, yet it really fills no more of true and genuine space, since if all the particular little spaces fill'd by these scatter'd Corpuscles were reduc'd into one, (as the Corpuscles themselves often are in Chymical Operations) they would amount but to one total space, equal to that of the whole Mercury before rarefaction. But these Objections against this Explication are not all that I have to say against our Adversaries Funiculus it self.

For I farther demand how the Funiculus comes by such hooks or graple-irons, or parts of the like shape, to take fast hold of all contiguous bodies, and even the smoothest, such as Glass, and the calm surface of Quicksilver, Water, Oyle, and other fluids: And how these slender and invisible hooks cannot onely in the tersest bodies find an innumerable company of ears or loops to take hold on, but hold so strongly that they are able not alone to lift up a tall Cylinder of that very ponderous metal [Page] of Quick-silver, but to draw inwards the sides of strong Glasses so forcibly, as to break them all to pieces. And 'tis also somewhat strange, that Water and other fluid bodies (whose parts are wont to be so easily separable) should, when the Funiculus once layes hold on the superficial Corpuscles, presently emulate the nature of consistent bodies, and be drawn up like Masses each of them of an intire piece; though even in the exhausted Receiver they appear by their undulation (when they are stir'd by Bubbles that pass freely through them) and many other signs to continue fluid bodies.

It seems also very difficult to conceive how this extenuated substance should require so strong a spring inward as the Examiner all along his books ascribes to it. Nor will it serve his turn to require of us in exchange an Explication of the Airs spring outward, since he acknowledges, as well as we, that it has such a spring. I know, that by calling this extenuated substance a Funiculus, he seems plainly to intimate that it has its spring inward, upon the same account that Lute-strings and Ropes forcibly stretch'd have theirs. But there is no small disparity betwixt them: for whereas in strings there is requir'd either wreathing, or some peculiar and artificial texture of the component parts; a rarefaction of Air (were it granted) does not include or infer any such contrivance of parts as is requisite to make bodies Elastical. And if the Cartesian Notion of the cause of Springiness be admitted, then our extenuated substance having no Pores to be pervaded by the materia subtilis (to which besides our Author also makes Glass impervious) will be destitute of Springiness. And however, since Lute-strings, Ropes, &c. must, when they shrink inwards, either fill up or lessen their Pores, and increase in thickness as they diminish in length; our Examiners Funiculus must differ very much from them, since it has no Pores to receive the shrinking parts, and contracts it self as to length, without increasing its thickness. Nor can it well be pretended that this self contraction is done ob fugam vacui, since though it should not be [Page] made, a Vacuum would not ensue. And if it be said that it is made that the preternaturally stretch'd Body might restore it self to its natural dimensions: I answer, That I am not very forward to allow acting for ends to Bodies inanimate, and consequently devoid of knowledge; and therefore should gladly see some unquestionable Examples produc'd of Operations of that nature. And however to me, who in Physical enquiries of this nature look for efficient rather than final causes, 'tis not easie to conceive how Air by being expanded (in which case its force (like that of other rarefi'd Bodies) seems principally to tend outwards, as we see in fired Gun-powder, in AEolipiles, in warm'd Weather-glasses, &c.) should acquire so prodigious a force of moving contiguous Bodies inwards. Nor does it to me seem very probable, that, when for instance part of a polish'd Marble is extended into a Funiculus, that Funiculus does so strongly aspire to turn into Marble again. I might likewise wish our Author had more clearly explicated, how it comes to pass (which he all along takes for granted) that the access of the outward Air does so much and so suddenly relax the tension of his Funiculus; since that being (according to him) a real and Poreless body, 'tis not so obvious how the presence of another can so easily and to so strange a degree make it shrink. But I will rather observe, that 'tis very unlikely that the space which our Adversary would have replenish'd with his Funicular substance, should be full of little highly-stretcht strings, that lay fast hold of the surfaces of all contiguous Bodies, and always violently endeavour to pull them inwards. For we have related in our 26. Experiment, that a Pendulum being set a moving in our exhausted Receiver, did swing to and fro as freely, and with the string stretch'd as streight, as for ought we could perceive it would have done in the common Air. Nay, the Balance of a Watch did there move freely and nimbly to and fro; which 'tis hard to conceive those Bodies could do, if they were to break through a medium consisting of innumerable exceedingly-stretched strings. On which occasion we might add, that 'tis somewhat strange that these strings, thus cut or broken by the passage [Page] of these bodies through them, could so readily have their parts re-united, and without any more ado be made intire again. And we might also take notice of this as another strange peculiarity in our Author's Funiculus, That in this case the two divided parts of each small string that is broken do not, like those of other broken strings, shrink and fly back from one another; but (as we just now said) immediately redintegrate themselves: Whereas, when in the Torricellian Experiment the Tube and contain'd Mercury is suddenly lifted up out of the restagnant Quicksilver into the Air, the Funiculus does so strangely contract it self, that it quite vanishes; insomuch that the ascending Mercury may rise to the very top of the Tube. These, I say, and divers other difficulties might on this occasion be insisted on; but that, supposing our selves to have mentioned enough of them for once, we think it now more seasonable to proceed to the remaining part of our Discourse.

CHAP. III. The Aristotelean Rarefaction (proposed by the Adversary) examin'd.

BUt this is not all that renders the Examiner's Hypothesis improbable: For, besides those already mentioned particulars, upon whose score it is very difficult to be understood; it necessarily supposes such a Rarefaction and Condensation, as is, I confess, to me, as well as to many other considering persons, unintelligible.

For the better discernment of the force of this Objection we must briefly premise, That a Body is commonly said to be rarefi'd or dilated, (for I take the word in a larger sense than, I know, many others do, for a reason that will quickly appear) when it acquires greater dimensions than the same Body had before; and to be condens'd, when it is reduc'd into less dimensions, that is, into a lesser space than it contain'd before: (as when a dry Spunge being first dipp'd in water swells to a far greater bulk, and then being strongly squeez'd and held compressed, is not only reduced into less room than it had [Page] before it was squeézed, but into less than it had even before it was wetted.) And I must further premise, That Rarefaction (as also Condensation) being amongst the most obvious Phaenomena of Nature, there are three (and for ought we know but three) ways of explicating it: For, either we must say with the Atomists and Vacuists, that the Corpuscles whereof the rarefied Body consists do so depart from each other, that no other substance comes in between them to fill up the deserted spaces that come to be left betwixt the incontiguous Corpuscles; or else we must say with divers of the ancient Philosophers, and many of the Moderns, especially the Cartesians, that these new Intervals produced betwixt the Particles of the raresied Body are but dilated Pores, replenished, in like manner as those of the tumid Spunge are by the imbibed water, by some subtile AEthereal substance, that insinuates it self betwixt the disjoyned Particles: Or, lastly, we must imagine with Aristotle and most of his followers, that the self-same Body does not only obtain a greater space in Rarefaction, and a lesser in Condensation, but adequately and exactly fill it, and so when rarefied acquires larger dimensions without either leaving any vacuities betwixt its component Corpuscles, or admitting between them any new or extraneous substance whatsoever.

Now 'tis to this last (and, as some call it, rigorous) way of Rarefaction that our Adversary has recourse in his Hypothesis: Though this, I confess, appear to me so difficult to be conceived, that I make a doubt whether any Phaenomenon can be explained by it; since to explain a thing is to deduce it from something or other in Nature more known than it self.

He that would meet with full Discussions of this Aristotelean Rarefaction, may resort to the learned writings of Gassendus, Cartesius and Maignan, who have accused it of divers great absurdities: But for my part, I shall at present content my self to make use to my purpose of two or three passages that I meet with (though not together) in our Author himself.

Let us then suppose, that in the Magdeburg Experiment he [Page] so often (though I think causlesly enough) urges to prove his Hypothesis; let us (I say) for easier considerations sake suppose, that the undilated Air, which (as he tells us) possessed about half an inch of space, consisted of a hundred Corpuscles, Pag. 42. or (if that name be in this case disliked) a hundred parts; (for it matters not what number we pitch upon) and 'twill not be denied, but that as the whole parcel of Air, or the Aggregate of this hundred Corpuscles, is adequate to the whole space it fills, so each of the hundred parts, that make it up, is likewise adequately commensurate to its peculiar space, which we here suppose to be a hundredth part of the whole space. This premised, our Author having elsewhere this passage, Corpore occupante locum verbi gratia duplo majorem, necesse est ut Pag. 160. quaelibet ejus pars locum quo (que) duplo majorem occupet; prompts us to subjoyn, that in the whole capacity of the Globe (which according to him was two thousand times as great as the room possessed by the unexpanded Air) there must likewise be two hundred thousand parts of space commensurate each of them to one of the fore-mentioned hundredth parts of Air; and consequently, when he affirms that that half Inch of Air possessed the whole cavity of the Globe, if we will not admit (as he does not) either Vacuities or some intervening subtile substance in the Interval of the Aërial parts, he must give us leave to conclude, that each part of Air does adequately fill two thousand parts of space. Now that this should be resolutely taught to be not only naturally possible, (for we dispute not here of what the Divine Omnipotence can do) but to be really and regularly done in this Magdeburg Experiment, will questionless appear very absurd to the Cartesians and those other Philosophers, who take Extension to be but notionally different from Body, and consequently impossible to be acquir'd or lost without the addition or detraction of Matter; and will, I doubt not, appear strange to those other Readers, who consider how generally Naturalists have looked upon Extension as inseparable, and as immediately flowing from matter; and upon Bodies, as having necessary relation to a commensurate space. Nor do I see, if one [Page] portion of Air may so easily be brought exactly to fill up a space two thousand times as big as that which it did but fill before without the addition of any new substance; I see not (I say) why the matter contained in every of these two thousand parts of space may not be further brought to fill two thousand more, and so onwards, since each of these newly-replenished spaces is presumed to be exactly filled with Body, and no Space, nor consequently that which the unrarefied Air replenished, can be more than adequately full. And since, according to our Adversary, not only fluid Bodies, as Air and Quicksilver, but even solid and hard ones, as Marble, are capable of such a Distension as we speak of, why may not the World be made I know not how many thousand times bigger than it is, without either admitting any thing of Vacuity betwixt its parts, or being increased with the addition of one Atome of new matter? Which to me is so difficult to conceive, that I have sometimes doubted, whether in case it could be proved, that in the exhausted Globe we speak of there were no Vacuities within, nor any subtile matter permitted to enter from without, it were not more intelligible to suppose that God had created a new matter to joyn with the Air in filling up the Cavity, than that the self-same Air should adequately fill two thousand spaces, whereof one was exactly commensurate to it even when it was uncompressed. For divers eminent Naturalists, both ancient and modern, believing upon a Physical account the Souls of men to be created and infused, will admit it as intelligible that God does frequently create substances on certain emergent occasions. But I know that many of them will not likewise think it conceivable, that without his immediate interposition an accession of new, real Dimensions should be had without either vacuities or accession of matter.

And indeed when I considered these difficulties and others, that attend the Rarefaction our Examiner throughout his whole Book supposes, and when I found that ever and anon he remits us to what he teaches concerning Rarefaction; I could not but with some greediness resort to the Chapters he addressed me to. [Page] But when I had perused them, I found the Difficulties remained such still, and that 'twas very hard even for a witty man to make more of a subject than the nature of it does bear. Which I say, that by professing my self unsatisfied with what he writes, I may not be thought to find fault with a man for not doing what perhaps is not to be done, and for not making such abstruse Notions plain, as are scarcely (if at all) so much as intelligible. And indeed as he has handled this subject modestly enough, so in some places his Expressions are to me somewhat dark; which I mention, not to impute it as a Crime in him, that he wrote in a diffident and doubtfull strain of so difficult a matter, but to excuse my self if I have not always guessed aright at his meaning.

The things he alledges in favour of the Rarefaction he would persuade are two: The one, That the Phaenomena of Rarefaction cannot be explicated either by Vacuities or the subingression of an AEthereal substance; and the other, That there are two ways of explicating the rigorous Rarefaction he contends for.

His Objections against the Epicurean and Cartesian ways of making out Rarefaction are some of them more plausible than most of those that are wont to be urged against them; yet not such as are not capable enough of Answers. But whilst some of the passages appeared easie to be replyed to by the Favourers of the Hypothesis they oppose, before I had fully examined the rest, chancing to mention these Chapters to an ingenious Man, hereafter to be further mentioned in this Treatise; he told me he had so far considered them more than the rest of the book, that he had thought upon some Hypotheses, whereby the Phaenomena of Rarefaction might be made out either according to the Vacuists, or according to the Cartesians, adding, that he had also examined the Instance our Adversary pretends to be afforded him of his Rarefaction by what happens in the Rota Aristotelica. Wherefore being sufficiently distressed by Avocations of several sorts, and being willing to reserve the Declaration of my own thoughts concerning the manner of Rarefaction and Condensation for another Treatise, I shall refer the Reader to [Page] the ingenious Conjectures about this Subject, which the Writer of them intends to annex to the present Discourse; and only add in general, That whereas the Examiner's Argument on this occasion is, That his way of Rarefaction must be admitted, because neither of the other two can be well made out, his Adversaries may with the same reason, argue that one of theirs is to be allowed, since his is incumbred with such manifest difficulties. And they may enforce what they say by representing, that the inconveniences that attend his Hypothesis about Rarefaction are insuperable, arising from the unintelligible nature of the thing it self; whereas those to which the other ways are obnoxious, may seem to spring but from mens not having yet discovered what kind of Figures and Motions of the small Particles may best qualifie them to make the Body that consists of them capable of a competent expansion.

After our Author's Objections against the two ways of Rarefaction proposed, the one by the Vacuists, and the other by the Cartesians and others, that admit the solidest Bodies, and even Glass it self, to be pervious to an AEthereal or subtile matter; he attempts to explicate the manner by which that rigorous Rarefaction he teaches is perform'd: and having premised, that the Explication of the way how each part of the rarefy'd Body becomes extended, depends upon the quality of the parts into which the Body is ultimately resolv'd; and having truly observ'd, that they must necessarily be either really indivisible, or still endlesly divisible; he endeavours to explicate the Aristotelean Rarefaction according to those two Hypotheses. But, though he thus propose two ways of making out his Rarefaction; yet besides that they are irreconcilable, he speaks of them so darkly and doubtfully, that it seems less easie to discern which of the two he would be content to stick to, than that he himself scarce acquiesces in either of them.

And, first, having told us how Rarefaction may be explain'd, in case we admit Bodies to be divisible in infinitum, he does himself make such an Objection against the infinity of parts in a continuum, as he is fain to give so obscure an Answer to, [Page] that I confess I do not understand it; and presume, that not only the most part of unprejudiced Readers will as little acquiesce in the Answer as I do; but even the Author himself will not marvel at my confession, since in the same place he acknowledges the Answer to be somewhat obscure, and endeavours to excuse its being so, because in that Hypothesis it can scarce be otherwise.

Wherefore I shall only add on this occasion, that 'tis not clear to me, that even such a divisibility of a continuum as is here supposed would make out the Rarefaction he contends for. For, let the integrant parts of a continuum be more or less finite or infinite in number, yet still each part, being a corporeal substance, must have some Particle of space commensurate to it; and if the whole Body be rarefied, for instance, to twice its former bigness, then will each part be likewise extended to double its former dimensions, and fill both the place it took up before, and another equal to it, and so two places.

The second Argument alledged to recommend the hitherto-mentioned way of explicating Rarefaction is, That many learned Men, amongst whom he names two, Aquinas and Suarez, have taught that the same corporeal thing may naturally be, and de facto often is, in the souls of Brutes really indivisible and virtually extended. But, though I pay those two Authors a just respect for their great skill in Scholastical and Metaphysical learning; yet the Examiner cannot ignore, that I could make a long Catalogue of Writers, both ancient and modern, at least as well vers'd in natural Philosophy as Saint Thomas and Suarez, who have some of them in express words denied this to be naturally possible; and others have declared themselves of the same judgment by establishing principles, with which this Conceit of the virtual extension of the indivisible Corpuscles is absolutely inconsistent. And though no Author had hitherto opposed it, yet I, that dispute not what this or that man thought, but what'tis rational to think, should nevertheless not scruple to reject it now; and should [Page] not doubt to find store of the best Naturalists of the same opinion with me, and perhaps among them the Examiner himself, who (however this acknowledgment may agree with the three following Chapters of his book) tells us, (pag. 160.) that Juxta probabiliorem sententiam hujusmodi virtualis extensio rei corporeae concedenda non est, utpote soli rei spirituali propria.

But to conclude at length this tedious Enquiry into the Aristotelean way of Rarefaction, (which is of so obscure a nature that it can scarce be either proposed or examined in few words) I will not take upon me resolutely to affirm which of the two ways of explicating it (by Atomes or by Parts infinitely divisible) our Author declares himself for. But which of them soever it be, I think I have shown that he has not intelligibly made it out: And I make the less scruple to do so, because he himself is so ingenuous as (at the close of his discourse of the two ways) to speak thus of the Opinion he prefers; Praestat communi & receptae hactenus in Scholis sententiae insistere, quae licet Pag 169. difficultates quidem non clarè solvat, iis tamen aperte non succumbit. So that in this discourse of Rarefaction, to which our Author has so often in the foregoing part of the Book referred us, as that which should make good what there seemed the most improbable; he has but instead of a probable Hypothesis needlesly rejected, substituted a Doctrine which himself dares not pretend capable of being well freed from the difficulties with which it may be charged; though I doubt not but other Readers, especially Naturalists, will think he has been very civil to this obscure Doctrine, in saying that Difficultatibus non aperte succumbit.

As for the other way of explicating Rarefaction, namely, by supposing that a body is made up of parts indivisible; he will not I presume, deny, but that the Objections we formerly made against it are weighty. For according to this Hypothesis (which one would think he prefers, since he makes use of it in the three or four last Chapters of his Book) Necessariò fatendum est (says he) unam eandem (que) partem poni Pag. 163. in duplici loco adaequate: Cum enim indivisibilis sit, locum (que) occupet majorem quam prius, necesse est ut tota sit in quolibet punato[Page]totius lici, sive ut per totum illud spatium virtualiter extendatur. So that when hein the very next Page affirms, that by this virtual extention of the parts, the Difficulties that have for so many Ages troubled Philosophers may be easily solved, he must give me leave (who love to speak intelligibly, and not to admit what I cannot understand) to desire he would explain to me what this extensto virtualis is, and how it will remove the Difficulties that I formerly charged upon the Aristotelean Rarefaction. For the easier consideration of this matter, let us resume what we lately supposed, namely, that in the Magdeburgick Experiment the half Inch of undilated Air consisted of a hundred Corpuscles; I demand how the indivisibility of these Corpuscles will qualifie them to make out such a Rarefaction as the Author imagines. For what does their being indivisible do in this case, but make it the less intelligible how they can fill above a hundred parts of space? 'Tis easie to foresee he will answer, That they are virtually extended. But not here to question how their indivisibility makes them capable of being so; I demand, whether by an Atoms being virtually extended, its corporeal substance do really (I mean adequately) fill more space than it did before, or whether it do not: (for one of the two is necessary.) If it do, then 'tis a true and real, and not barely a virtual extension. And that such an extension will not serve the turn, what we have formerly argued against the Peripatetick Rarefaction will evince; and our Adversary seems to consess as much, by devising this virtual extension to avoid the inconveniences to which he saw his Doctrine of Rarefaction would otherwise plainly appear expos'd. But if it be said, That when an Atome is virtually extended, its corporeal substance fills no more space than before: This is but a Verbal shift, that may perhaps amuse an unwary Reader, but it will scarce satisfie a considering one. For I demand how that which is not a substance can fill place; and how this improper and but Metaphorical Extension will salve the Phaenomena of Rarefaction: as how the half Inch of Air at the top of the fore-mentioned Globe shall without a corporeal [Page] extension fill the whole Globe of two thousand times its bigness when the water is suck'd out of it, and act at the lower part of the Globe. Which last Clause I therefore add, because not only our Author teaches (pag. 91. and 92.) that the whole Globe was filled with a certain thin substance, which by its contraction violently snatch'd up the water into which the neck of the Glass was immers'd; but in a parallel case he makes it his grand Argument to prove, that there is no Vacuum in the deserted part of the Tube in the Torricellian Experiment, That the attraction of the Finger cannot be performed Chap. 5. but by some real Body. Wherefore till the Examiner do intelligibly explain how a virtual Extension, as it is opposed to a corporeal, can make an Atome fill twice, nay, two thousand times more space than it did before; I suppose this device of virtual extension will appear to unbiass'd Naturalists but a very unsatisfactory evasion.

Two Arguments indeed there are which our Adversary offers as proofs of what he teaches. The first is, That they commonly teach in the Schools, that at least divinitus (as he speaks) such a thing as is pleaded for may be done, and that consequently it is not repugnant to the nature of a body. But, though they that either know me, or have read what I have written about matters Theological, will, I hope, readily believe, that none is more willing to acknowledge and venerate Divine Omnipotence; yet in some famous Schools they teach, that it is contrary to the nature of the thing. And that men who think so, and consequently look not upon it as an object of Divine Omnipotence, may (whatever he here say) without impiety be of a differing mind from him about the possibility of such a Rarefaction as he would here have, our Author may perchance think fit to grant, if he remember that he himself says a few Pages after, Cum tempus sit Ens essentialiter successivum, it a ut ne divinitus Pag. 175. quidem possint duae ejus partes simul existere, &c. But, not now to dispute of a power that I am more willing to adore than question, I say, that our Controversie is not what God can do, but about what can be done by Natural Agents, not [Page] elevated above the sphere of Nature. For though God can both create and annihilate, yet Nature can do neither: and in the judgment of true Philosophers I suppose our Hypothesis would need no other advantage to make it be preferred before our Adversaries, than that in ours things are explicated by the ordinary course of Nature, whereas in the other recourse must be had to miracles.

But though our Author's way of explicating Rarefaction be thus improbable, yet I must not here omit to take notice, that his Funiculus supposes a Condensation that to me appears incumbred with no less manifest difficulties. For, since he teaches that a body may be condens'd without either having any vacuities for the comprest parts to retire into, or having Pores filled with any subtile and yielding matter that may be squeez'd out of them; it will follow, that the parts of the Body to be condens'd do immediately touch each other: which supposed, I demand how Bodies that are already contiguous can be brought to farther Approximations without penetrating each other, at least in some of their part. So that I see not how the Examiners Condensation can be perform'd without penetration of dimensions. A thing that Philosophers of all Ages have looked upon as by no means to be admitted in Nature. And our Author himself speaks somewhere at the same rate, where to the Question, Why the walls that inclose fired Gun-powder must be blown asunder? Respondeo (says he) haec omnia inde accidere, quod pulvis ille sic accensus & in flammam conversus, Pag. 159. longe majus spatium nunc occupet quàm prius. Vnde fit, ut cum totum cubiculum antea fuerit plenissimum, disrumpantur sic parietes, ne detur corporum penetratio. In the Magdeburgick Experiment he tells us (as we have heard already) that the whole capacity of the Globe is filled with an extremely-thin body. But not now to examine how properly he calls that a rare body, which according to him intercepts neither Pores nor any heterogeneous substance, the greater or lesser absence of which makes men call a Body more or less dense; not to insist on this, I say, let us consider, that before the admission of water into [Page] the exhausted Globe there was, according to him, two thousand half Inches of a substance, which, however it was produc'd or got thither, was a true and real Body; and that after the admission of the water there remained in the same Globe, besides the water that came in, no more than one half Inch of body. Since then our Author does not pretend (which if he did, might be easily disproved) that the one thousand nine hundred ninety nine half Inches of Matter, that now appear no more, traversed the body of Water; since he will not allow that it gets away through the Pores of the Glass, I demand, what becomes of so great a quantity of Matter? For that 'tis annihilated I suppose he is too rational a man to pretend, (nor, if he should, would it be at all believ'd) and to say, that a thousand and so many hundred parts of Matter should be retir'd into that one part of space that contains the one half Inch of Air, is little less incredible: For that space was suppos'd perfectly full of body before, and how a thing can be more than perfectly full, who can conceive? To dispatch: According to our Author's way of Condensation, two, or perhaps two thousand, Bodies may be crouded into a space that is adequately fill'd by one of them apart. And if this be not penetration of Dimensions, I desire to be informed what is so; and till then I shall leave it to any unprepossess'd Naturalist to judge, whether an Hypothesis that needs suppose a thing so generally concluded to be impossible to Nature, be probable or not; and whether to tell us that the very same parcel of Air, that is now without violence contain'd in half an Inch of space, shall by and by fill two thousand times as much room, and presently after shrink again into the two thousandth part of the space it newly possess'd, be not to turn a Body into a Spirit, and, confounding their Notions, attribute to the former the discriminating and least easily conceivable properties of the later. And this Argument is, I confess, with me of that weight, that this alone would keep me from admitting the Examiners Hypothesis: Yet if any happier Contemplator shall prove so sharp-sighted, as to devise and clearly propose a way of making the Rarefaction and Condensation [Page] hitherto argued against, intelligible to me, he is not like to find me obstinate. Nor indeed is there sufficient cause why his succeeding in that attempt should make our Adversaries Hypothesis preferrable to ours, since that would not prove it either necessary, or so much as sufficient, but only answer some of the Arguments that tend to prove 'its not intelligible. And that we have other Arguments on our side than those that relate to Rarefaction and Condensation, may appear partly by what has been discours'd already, and partly by what we have now to subjoyn.

CHAP. IV. A Consideration (pertinent to the present Controversie) of what happens in trying the Torricellian and other Experiments, at the tops and feet of Hills.

THere remain then yet a couple of Considerations to be oppos'd against the Examiners Hypothesis, which, though the past Discourse may make them be look'd upon as needless, we must not pretermit, because they contain such Arguments as may not only be imployed against our Adversaries Doctrine, but will very much tend to the confirmation of ours.

I consider then further, that the Hypothesis I am opposing, being but a kind of Inversion of ours, and supposing the spring or motion of Restitution in the Air to tend inwards, as according to us it tends outwards; it cannot be, that if the supposition it self were (what I think I have prov'd it is not) true, many of the Phaenomena would be plausibly enough explicable by it: the same motions in an intermediate body being in many cases producible alike, whether we suppose it to be thrust or drawn; provided both the endeavours tend the same way. But then we may be satisfied whether the effect be to be ascribed to Pulsion or to Traction, (as they commonly speak, though indeed the later seems reducible to the former) if we can find out an Experiment wherein there is reason such an effect should follow, in case Pulsion be the cause inquired after, and not in case it be Traction. And such an Experimentum Crucis (to speak with our Illustrious[Page]Verulam) is afforded us by that noble Observation of Monsieur Paschal, mentioned by the famous Pecquet, and out of him by our Author: namely, that the Torricellian Experiment Pag. 66. being made at the foot and in divers places of a very high Mountain, (of the altitude of five hundred fathom or three thousand foot) he found, that after he had ascended a hundred and fifty Fathom, the Quicksilver was fallen two Inches and a quarter below its station at the Mountains foot; and that at the very top of the Hill it had descended above three Inches below the same wonted station. Whence it appears that the Quicksilver being carried up towards the top of the Atmosphere, falls down the lower, the higher the place is wherein the observation is made: of which the reason is plain in our Hypothesis, namely, that the nearer we come to the top of the Atmosphere, the shorter and lighter is the Cylinder of Air incumbent upon the restagnant Mercury; and consequently the less weight of Cylindrical Mercury will that Air be able to counterpoise and keep suspended. And since this notable Phaenomenon does thus clearly follow upon ours, and not upon our Adversaries Hypothesis; this Experiment seems to determine the controversie betwixt them: because in this case the Examiner cannot pretend, as he does in the seventeenth and divers other of our Experiments, that the descent of the Quicksilver in the Tube is caus'd, not by the diminution of the external Airs pressure, but from the preternatural Rarefaction or Distension of that external Air (in the Receiver) when by seeking to restore it self, it endeavours to draw up the restagnant Mercury: For in our present case there appears no such forcible Dilatation of that Air, as in many of the Phaenomena of our Engine he is pleas'd to imagine.

It need therefore be no great wonder, if his Adversaries do, as he observes, make a great account of this Experiment, to prove that the Mercury is kept up in the Tube by the resistance of the external Air. Nor do I think his Answers to the Argument drawn from hence will keep them from thinking it cogent. For to an Objection upon which he takes notice that they lay so much stress, he replies but two things; [Page] which neither singly nor together will near amount to a satisfactory Answer.

And, First, he questions the truth of the Observation it self; because having made trial in a low Hill, the event did no ways answer his expectation. But though, in stead of disapproving, I am willing to commend his Curiosity, to make the Experiment himself, and especially since 'twas both new and important; and though also I like his Modesty, in rather suspecting some mistake in the manner of the Observation, than that the Experimenters did not sincerely deliver it: yet, since there must be an Error somewhere, I must rather charge it upon the Examiners observation (I say his Observation, not his want of sincerity) than upon Monsieur Paschal's. For besides the commendations that the learned Gassendus, who relates the Experiment, gives to that ingenious Gentleman (Monsieur Paschal) by whose direction he supposes it to have been try'd: the same Gassendus relates, that the like Observation was five times repeated, partim intra sacellum, partimaëre Gassendus Tomo. 1. pag. 211. libero, & nunc quidem flante, nunc silente vento. Which circumstances sufficiently argue the Diligence where with the Experiment was try'd in Auvergne. Especially since I can confirm these Observations by two more made on distant Hills in England: the one of which I procur'd from that known Virtuoso Mr. J. Ball, whom I desir'd to make the Experiment at a Mountain in Devonshire, on the side whereof he dwelt; and the other made in Lancashire by that ingenious Gentleman Mr. Rich. Townley. Both which Observations, since I have mention'd them at large in the Appendix to the Physico Mechanical Treatise, shall not now repeat; contenting my self to observe to our present purpose, that however the proportion of the Descent of the Quicksilver may vary, according to the differing consistence and other accidents of the neighbouring Air, in the particular places and times of the Experiments being made, yet all Observations agree in this, That nearer the top of the Atmosphere the Quicksilver falls lower than it does further from it. To all this I shall add two things that will very much confirm our [Page] Hypothesis. The one is, that the freshly-nam'd Mr. Townley, and divers ingenious Persons that assisted at the Tryal, bethought themselves of so making the Torricellian Experiment at the top of the Hill, as to leave a determinate quantity of Air in the Tube, before the mouth of it was open'd under the vessell'd Mercury; and taking notice how low such a quantity of that Air depressed the Mercurial Cylinder, they likewise observ'd, that at the Mountains foot the included Air was not able to depress the Quicksilver so much. Whence we inferre, that the Cylinder of Air at the top of the Hill being shorter and lighter, did not so strongly press against the included Air, as did the ambient Air at the bottom of the Hill, where the Aëreal Cylinder was longer and heavier.

But because that though Experiments made in very elevated places are noble ones, and of great importance in the Controversies about the Air, yet there are but very few of those that are qualified to make Experiments of that Nature, who have the opportunity of making them upon high Mountains; we did with the assistance of an ingenious man attempt a Tryal, wherein we hoped to find a sensibly-differing Weight of the Atmosphere, in a far less height than that of an ordinary Hill. But in stead of a common Tube we made use of a kind of Weather-glass, that the included Air might help to make the event notable, for a reason to be mentioned ere long; and in stead of Quicksilver we employ'd common Water in the Pipe belonging to the Weather-glass, that small changes in the Weight or resistance of the Atmosphere in opposition of the included Air might be the more discernable. The Instrument we made use of consisted onely of a Glass with a broad Foot and a narrow Neck (AB) and a slender Glass-Pipe (CD) open at both ends: which Pipe was so placed, that the bottom of it did almost, but not quite, reach to the bottom of the bigger Glass (AB) within whose Neck (A) it was fastned with a close cement, that both kept the Pipe in its place, and hindred all communication betwixt the inward (II) and ou [...]ward (KK) Air, save by the cavity of the Pipe (CD). Now we chose [Page] this Glass (AB) more than ordinary capacious, that the effect of the dilatation of the included Air (II) might be the more conspicuous. Then conveying a convenient quantity of Water (HH) into this Glass, we carried it to the Leads of the lofty Abby-Church at Westminster, and there blew in a little Air to raise the Water to the upper part of the Pipe, that being above the Vessel (AB) we might more precisely mark the several stations of the Water than otherwise we could. Afterward having suffered the Glass to rest a pretty while upon the Lead, that the Air (II) within might be reduc'd to the same state, both as to coldness and as to pressure, with (KK) that without, having marked the station of the Water (F), we gently let down the Vessel by a long string to the foot of the Wall, where one attended to receive it; who having suffer'd it to rest upon the ground, cry'd to us that it was subsided about an Inch below the mark (F) we had put: whereupon having order'd him to put a mark at his second station of it (E), we drew up the Vessel again; and suffering it to rest a while, we observ'd the Water to be re-ascended to or near the first mark (F), which was indeed about an Inch above (E) the other. And this we did that Evening a second time with almost a like success: though two or three dayes after, the wind blowing strongly upon the Leads, we found not the Experiment to succeed quite so regularly as before; yet the Water alwayes manifestly fell lower at the foot of the Wall than it was at the top: which I see no cause to ascribe barely to the differing temperature of the Air above and below, as to Heat and Cold, since according to the general estimate, the more elevated Region of the Air is, caeteris paribus, colder than that below, which would rather check the greater expansion of the included Air at the top of the Leads than promote it. But the better to avoid mistakes and prevent Objections, we thought fit to try the Experiment within the Church, and got into a Galery of the same height with the Leads: but the upper part of the Pipe being casually broken off, we thought fit to order the matter so, that the surface (G) of the remaining Water in the Pipe should be about [Page] [Page]

[figure]

[Page] an Inch higher than the surface of the Water in the Vessel. And then my above-mentioned Correspondent letting down the Glass, almost as soon as it was setled upon the pavement, kneeling down to see how far it was subsided, I found that not onely it was fallen as low as the other Water, but that the outward Air deprest it so far, as whilst I was looking on, to break in beneath the bottom of the Pipe, and ascend through the Water in bubbles; after which the Glass being drawn up again, my Correspondent affirm'd, that the Water was very manifestly re-ascended. But because by the unlucky breaking of a Glass, we were hindred to observe, as we designed, what would happen as well in a Weather-glass, so contriv'd that the weight or pressure of the Atmosphere should make no change in it, as in another whose included Air was at the top, (whereas in that we imploy'd the included Air was in the lower part,) and because there happened in our Tryals a Circumstance or two that seem'd not so devoid of difficulties, but that we think it may require further examination, we design to set down a more particular account of this Experiment, (as how it succeeds with Quicksilver instead of Water, together with the capacity of the Vessel (AB) and the bore of the Pipe (CD) with some other variety of Circumstances) together with the event of the curiosity we had (which seemed very successfull) to try the Torricellian Experiment upon the above-mentioned Leads, and then let down the Tube together with the restagnant Mercury to the ground, to observe the increasing altitude of the Quicksilver, in the formerly-mentioned Appendix to the Epistle we have been defending. And it shall suffice us in the mean time that the Tryals already mentioned seem to make it evident enough that the Atmosphere gravitates more, caeteris paribus, near the surface of the Earth, than in the more elevated parts of the Air. For the Leads on which we made our Tryals were found by measure to be in perpendicular height but threescore and fifteen Foot from the ground. To which we shall onely add this at present, that once being desirous to observe what we could touching the proportions of the subsidence of the Water to the [Page] height of its several stations from the ground, purposely carrying down the Vessel so as not considerably to heat it, from the Leads down the stairs to a little window that we guest to be almost half way to the bottom, we there perceived the water to have already subsided about a Barly-Corns length, notwithstanding that probably in spite of our care, the Vessel were a little warmed by the heat of his body that carried it, since by that time we were come to the foot of the Wall, the Water stood almost at the highest mark; but after the Vessel was suffered to rest a while, it relapsed by degrees to the lowest. And thus much for the first of the things I had to represent in favour of our Doctrine.

The other Particular I shall mention for confirmation of our Hypothesis, is that Experiment (which, though it be needless, seems yet more cogent and proper to prevent Evasions) made by the same Mousieur Paschal, of carrying a weakly-blown Foot-ball from the bottom to the top of an high Mountain. For that Foot-ball swell'd more and more, the higher it was carried, so that it appeared as if it were full blown at the top of the Mountain, and gradually growing lank again, as it was carried downwards; so that at the foot of the Hill it was flaccid as before. This, I say, having thus happened, we have here an Experiment to prove our Hypothesis, wherein recourse cannot be had to any forcibly and preternaturally distended Body, such as that is pretended to be which remains in the deserted space of the Tube in the Torricellian Experiment.

The other thing which the Examiner alledges against our Argument from Monsieur Paschal's Tryals, is, that supposing it to be true, yet it cannot thence be inferr'd, that the subsidence of the Mercury at the top of the Hill proceeded from the Atmospherical Cylinder's being there lighter and less able to sustain the Quicksilver. Sed dici potest (sayes he) ideo sic in vertice Montis magis descendisse, quod ibidem esset Page 63. Aura frigidior, aut ex alio Temperamento hujusmodi descensum causante. But this solution will not serve the turn: For the coldnes, of the ambient Air (which yet the Experimenters take not [Page] notice of) would rather contract the rarefied substance within the Tube, and so draw up the Mercury higher, as our Author himself teaches us, that 'tis from the shrinking of the Funiculus occasion'd by the cold that the Water in Thermometers ascends in cold weather. And whereas the onely Pag. 50. proof he addes of so improbable an Explication is taken from our eighteenth Experiment, wherein we relate, that sometimes the Quicksilver did sensibly fall lower in colder than in far less cold weather: I answer, that this eighteenth Experiment will scarce make more for him than against him: For, as I there take notice that the Quicksilver descended in cold weather, so it sometimes descended likewise in hot weather, and rose in cold. And 'tis very strange, that in all the Observations made, in differing Countries and at diffe ing times, it should still so happen that the Mercurial Cylinder should be shorter near the top of the Atmosphere than further from it; if the resistance of the outward Air have nothing to do with the keeping it suspended. And 'tis yet more strange, that the foot-ball should in like manner grow turgid and flaccid, according as it is carried into places where it has a shorter or longer Pillar of Air incumbent on it.

I was going to proceed to what remains of this second Part of our Treatise, But that since I begun this Chapter casually meeting with an Experiment lately sent in a Letter to a very Ingenious Mr. Croon one of the learned Professors of Gresham College. Acquaintance of his and mine by a very Industrious Physician Dr. Hen. Power. (who is said to have had the curiosity to try over again many of the Experiments of our Engine) and finding it very proper to confirm our newly related Experiment made at Westminster, and to be of such a nature as we have not in this part of England the opportunity to try the like, for want of Hills high enough, I shall (according to the permission given me) insert it in this place. And the rather, that as the Mountains have by the Tryals made on them of the Torricellian Experiment, afforded us a noble proof of the weight of the Air; so they may afford us one of its Spring: [Page] wherein I hope the Phaenomenon of the Waters descent will not be ascribed to any attraction made of the Water by the violentlydistended outward Air. And because the Experiment was not made by us, but by another, we will set it down in his words, which are these: This fifteenth of October 1661. we took a Weather glass A B, of about two See the second Figure. foot in length, and carrying it to the bottom of Hallifax Hill, the Water stood in the shank at thirteen Inches above the Water in the Vessel: Thence carrying it thus fill'd, with the whole frame, immediately to the top of the said Hill, the Water fell down to the point D, viz. an Inch and a quarter lower than it was at the bottom of the said Hill; which (as he rightly inferrs) proves the Elasticity of the Air: for the internal Air A C, which was of the same power and extension with the external at the bottom of the Hill, did manifest a greater Elasticity than the Mountain-Air there Probably these or the like words, did manifest Pressure, are here omitted, for the Mountain-Air there seems to have acted rather by its Weight than Elasticity., and so extended it self further by C D.

The like Experiment, I hear, the same Ingenious Doctor has very lately repeated, and found the descent of the Water to be greater than before. And though some Virtuosi have thought it strange, that in an Hill far inferiour to the Alps and Appennines, so short a Cylinder of so light a liquor as Water should fall so much; yet I see not any reason to distrust upon this ground either His Experiment or Ours (lately mention'd to have been made at Westminster;) but rather to wonder the Water fell not more (if the Hill be considerably high:) for their suspicion seems grounded upon a mistake, as if because the Quicksilver in the Torricellian Experiment made without purposely leaving any Air in the Tube, would not, at the top of the mention'd Hill, have subsided above an Inch, if so much, the Water, that is near fourteen times lighter, should not fall above a sourteenth part of that space; whereas in the Torricellian Experiment, the upper and deserted space of the Tube has little or no Air left in it, but the Correspondent part of the Weather-glass was furnish'd with Air, whose [Page] pressure was little less than that of the Atmosphere at the bottom of the Hill; and consequently must be much greater than the pressure of the Atmosphere at the top of the Hill, where the Atmospherical Cylinder's gravity (upon whose account it presses) must be much diminish'd by its being made much shorter, and by its consisting of an Air less comprest. And thus much for the first of the two Considerations wherewith I promised to conclude this second part of the present Tract. Onely before I proceed I must in a word desire the Reader to take notice, that though I have here singled out but one of the nine Experiments which the Examiner in the 11. and 12. Chapters reckons up as urg'd by his Adversaries; yet do not thereby declare my acquiescing in his Explications of those Phaenomena, but onely leave both them and some other things he delivers about Siphons and the Magdeburg Experiments, to be discours'd by those that are more concerned to examine them, contenting my self to have sufficiently disproved the Funiculus which his Expositions suppose, and cleared the grounds of explicating such Experiments aright.

CHAP. V. Two new Experiments touching the measure of the Force of the Spring of Air compress'd and dilated.

THE other thing that I would have considered touching our Adversaries Hypothesis is, That it is needless. For whereas he denies not that the Air has some Weight and Spring, but affirms that it is very insufficient to perform Pag. 11. such great matters as the counterpoising of a Mercurial Cylinder of 29. Inches, as we teach that it may: We shall now endeavour to manifest by Experiments purposely made, that the Spring of the Air is capable of doing far more than 'tis necessary for us to ascribe to it, to salve the Phaenomena of the Torricellian Experiment.

We took then a long Glass-Tube, which by a dexterous hand and the help of a Lamp was in such a manner crooked at the bottom, that the part turned up was almost parallel to the rest [Page] of the Tube, and the Orifice of this shorter leg of the Siphon (if I may so call the whole Instrument) being Hermetically seal'd, the length of it was divided into Inches, (each of which was subdivided into eight parts) by a streight list of paper, which containing those Divisions was carefully pasted all along it: then putting in as much Quicksilver as served to fill the Arch or bended part of the Siphon, that the Mercury standing in a level might reach in the one leg to the bottom of the divided paper, and just to the same height or Horizontal line in the other; we took care, by frequently inclining the Tube, so that the Air might freely pass from one leg into the other by the sides of the Mercury, (we took (I say) care) that the Air at last included in the shorter Cylinder should be of the same laxity with the rest of the Air about it. This done, we began to pour Quicksilver into the longer leg of the Siphon, which by its weight pressing up that in the shorter leg, did by degrees streighten the included Air: and continuing this pouring in of Quicksilver till the Air in the shorter leg was by condensation reduced to take up but half the space it possess'd (I say, possess'd, not fill'd) before; we cast our eyes upon the longer leg of the Glass, on which was likewise pasted a list of paper carefully divided into Inches and parts, and we observed, not without delight and satisfaction, that the Quicksilver in that longer part of the Tube was 29. Inches higher than the other. Now that this Observation does both very well agree with and confirm our Hypothesis, will be easily discerned by him that takes notice what we teach, and Monsieur Paschal and our English friends Experiments prove, that the greater the weight is that leans upon the Air, the more forcible is its endeavour of Dilatation, and consequently its power of resistance, (as other Springs are stronger when bent by greater weights.) For this being considered, it will appear to agree rarely-well with the Hypothesis, that as according to it the Air in that degree of density and correspondent measure of resistance to which the weight of the incumbent Atmosphere had brought it, was able to counterbalance and resist the pressure of a Mercurial Cylinder of about 29. [Page] Inches, as we are taught by the Torricellian Experiment; so here the same Air being brought to a degree of density about twice as great as that it had before, obtains a Spring twice as strong as formerly. As may appear by its being able to sustain or resist a Cylinder of 29 Inches in the longer Tube, together with the weight of the Atmospherical Cylinder, that lean'd upon those 29 Inches of Mercury; and, as we just now inferr'd from the Torricellian Experiment, was equivalent to them.

We were hindered from prosecuting the trial at that time by the casual breaking of the Tube. But because an accurate Experiment of this nature would be of great importance to the Doctrine of the Spring of the Air, and has not yet been made (that I know) by any man; and because also it is more uneasie to be made than one would think, in regard of the difficulty as well of procuring crooked Tubes fit for the purpose, as of making a just estimate of the true place of the Protuberant Mercury's surface; I suppose it will not be unwelcome to the Reader, to be informed that after some other trials, one of which we made in a Tube whose longer leg was perpendicular, and the other, that contained the Air, parallel to the Horizon, we at last procured a Tube of the Figure exprest in the Scheme; which Tube, though See the 5. Figure. of a pretty bigness, was so long, that the Cylinder whereof the shorter leg of it consisted admitted a list of Paper, which had before been divided into 12 Inches and their quarters, and the longer leg admitted another list of Paper of divers foot in length, and divided after the same manner: then Quicksilver being poured in to fill up the bended part of the Glass, that the surface of it in either leg might rest in the same Horizontal line, as we lately taught, there was more and more Quicksilver poured into the longer Tube; and notice being watchfully taken how far the Mercury was risen in that longer Tube, when it appeared to have ascended to any of the divisions in the shorter Tube, the several Observations that were thus successively made, and as they were made set down, afforded us the ensuing Table.

[Page]

A Table of the Condensation of the Air

A | A | B | C | D | E
48 | 12 | 00 | Added to 29⅛ makes | 29 2/16 | 29 2/16
46 | 11½ | 01 7/16 | 30 9/16 | 30 6/16
44 | 11 | 02 13/16 | 31 15/16 | 31 12/16
42 | 10½ | 04 6/16 | 33 8/16 | 33 1/7
40 | 10 | 06 3/16 | 35 5/16 | 35--
38 | 9½ | 07 14/16 | 37-- | 36 15/19
36 | 9 | 10 2/16 | 39 5/16 | 38⅞
34 | 8½ | 12 8/16 | 41 10/16 | 41 2/17
32 | 8 | 15 1/16 | 44 3/16 | 43 11/16
30 | 7½ | 17 15/16 | 47 1/16 | 46⅗
28 | 7 | 21 3/16 | 50 5/16 | 50--
26 | 6½ | 25 3/16 | 54 5/16 | 53 10/13
24 | 6 | 29 11/16 | 58 13/16 | 58 2/8
23 | 5 ¾ | 32 3/16 | 61 5/16 | 60 18/23
22 | 5½ | 34 15/16 | 64 1/16 | 63 6/11
21 | 5 ¼ | 37 15/16 | 67 1/16 | 66 4/7
20 | 5 | 41 9/16 | 70 11/16 | 70--
19 | 4 ¾ | 45-- | 74 2/16 | 73 11/19
18 | 4½ | 48 12/16 | 77 14/16 | 77 ⅔
17 | 4 ¼ | 53 11/16 | 82 12/16 | 82 4/17
16 | 4 | 58 2/16 | 87 14/16 | 87 ⅜
15 | 3 ¾ | 63 15/16 | 93 1/16 | 93 ⅕
14 | 3 ½ | 71 5/16 | 100 7/16 | 99 6/7
13 | 3 ¼ | 78 11/16 | 107 13/16 | 107 7/13
12 | 3 | 88 7/16 | 117 9/16 | 116 4/8

AA. The number of equal spaces in the shorter leg, that contained the same parcel of Air diversly extended.

B. The height of the Mercurial Cylinder in the longer leg, that compress'd the Air into those dimensions.

C. The height of a Mercurial Cylinder that counterbalanc'd the pressure of the Atmosphere.

D. The Aggregate of the two last Columns B and C, exhibiting the pressure sustained by the included Air.

E. What that pressure should be according to the Hypothesis, that supposes the pressures and expansions to be in reciprocal proportion.

For the better understanding of this Experiment it may not be amiss to take notice of the following particulars:

1. That the Tube being so tall that we could not conveniently make use of it in a Chamber, we were fain to use it on a pair of Stairs, which yet were very lightsome, the Tube being for preservations sake by strings so suspended, that it did scarce touch the Box presently to be mentioned.

2. The lower and crooked part of the Pipe was placed in a square wooden Box, of a good largness and depth, to prevent [Page] the loss of the Quicksilver that might fall aside in the transfusion from the Vessel into the Pipe, and to receive the whole Quicksilver in case the Tube should break.

3. That we were two to make the Observation together, the one to take notice at the bottom how the Quicksilver rose in the shorter Cylinder, and the other to pour in at the top of the longer, it being very hard and troublesome for one man alone to do both accurately.

4. That the Quicksilver was poured in but by little and little, according to the direction of him that observed below, it being, far easier to pour in more, than to take out any in case too much at once had been poured in.

5. That at the beginning of the Operation, that we might the more truly discern where the Quicksilver rested from time to time, we made use of a small Looking-glass, held in a convenient posture to reflect to the eye what we desired to discern.

6. That when the Air was so compress'd, as to be crouded into less than a quarter of the space it possess'd before, we tryed whether the cold of a Linen Cloth dipp'd in Water would then condense it. And it sometimes seemed a little to shrink, but not so manifestly as that we dare build any thing upon it. We then tried likewise whether heat would notwithstanding so forcible a compressure dilate it, and approaching the flame of a Candle to that part where the Air was pent up, the heat had a more sensible operation than the cold had before; so that we scarce doubted but that the expansion of the Air would, notwithstanding the weight that opprest it, have been made conspicuous, if the fear of unseasonably breaking the Glass had not kept us from increasing the heat.

Now although we deny not but that in our Table some particulars do not so exactly answer to what our formerly-intimated Hypothesis might perchance invite the Reader to expect; yet the Variations are not so considerable, but that they may probably enough be ascribed to some such want of exactness as in such nice Experiments is scarce avoidable. But for all [Page] that, till further trial hath more clearly informed me, I shall not venture to determine whether or no the intimated Theory will hold universally and precisely, either in Condensation of Air, or Rarefaction: All that I shall now urge being, That however, the trial already made sufficiently proves the main thing for which I here alledge it; since by it 'tis evident, that as common Air when reduc'd to half its wonted extent, obtained near about twice as forcible a Spring as it had before; so this thus comprest Air being further thrust into half this narrow room, obtained thereby a Spring about as strong again as that it last had, and consequently four times as strong as that of the common Air. And there is no cause to doubt, that if we had been here furnisht with a greater quantity of Quicksilver and a very strong Tube, we might by a further compression of the included Air have made it counterbalance the pressure of a far taller and heavier Cylinder of Mercury. For no man perhaps yet knows how near to an infinite compression the Air may be capable of, if the compressing force be competently increas'd. So that here our Adversary may plainly see that the Spring of the Air, which he makes so light of, may not only be able to resist the weight of 29 Inches, but in some cases of above an hundred Inches of Quicksilver, and that without the assistance of his Funiculus, which in our present case has nothing to do. And to let you see that we did not (a little above) inconsiderately mention the weight of the incumbent Atmospherical Cylinder as a part of the weight resisted by the imprisoned Air, we will here annex, that we took care, when the Mercurial Cylinder in the longer leg of the Pipe was about an hundred Inches high, to cause one to suck at the open Orifice; whereupon (as we expected) the Mercury in the Tube did notably ascend. Which considerable Phaenomenon cannot be ascribed to our Examiners Funiculus, since by his own confession that cannot pull up the Mercury, if the Mercurial Cylinder be above 29 or 30 Inches of Mercury. And therefore we shall render this reason of it, That the pressure of the incumbent Air being in part taken off by its expanding itself [Page] into the Suckers dilated Chest; the' imprison'd Air was thereby enabled to dilate it self manifestly, and repel the Mercury that comprest it, till there was an equality of force betwixt the strong Spring of that comprest Air on the one part, and the tall Mercurial Cylinder, together with the contiguous dilated Air, on the other part.

Now, if to what we have thus delivered concerning the compression of Air we add some Observations concerning its spontaneous Expansion, it will the better appear how much the Phaenomena of these Mercurial Experiments depend upon the differing measures of strength to be met with in the Air's Spring, according to its various degrees of compression and Laxity. But, before I enter upon this subject, I shall readily acknowledge that I had not reduc'd the trials I had made about measuring the Expansion of the Air to any certain Hypothesis, when that ingenious Gentleman Mr. Richard Townley was pleased to inform me, that having by the perusal of my Physico-Mechanical Experiments been satisfied that the Spring of the Air was the cause of it, he had endeavoured (and I wish in such attempts other ingenious men would follow his example) to supply what I had omitted concerning the reducing to a precise estimate how much Air dilated of it self loses of its Elastical force, according to the measures of its Dilatation. He added, that he had begun to set down what occurred to him to this purpose in a short Discourse, whereof he afterwards did me the favour to shew me the beginning, which gives me a just Curiosity to see it perfected. But, because I neither know, nor (by reason of the great distance betwixt our places of residence) have at present the opportunity to enquire, whether he will think fit to annex his Discourse to our Appendix, or to publish it by it self, or at all; and because he hath not yet, for ought I know, met with fit Glasses to make an any-thing-accurate Table of the Decrement of the force of dilated Air; our present design invites us to present the Reader with that which follows, wherein I had the assistance of the same person that I took notice of in the former Chapter, as having written [Page] something about Rarefaction: whom I the rather make mention of on this occasion, because when he first heard me speak of Mr. Townley's suppositions about the proportion wherein Air loses of its Spring by Dilatation, he told me he had the year before (and not long after the publication of my Pneumatical Treatise) made Observations to the same purpose, which he acknowledged to agree well enough with Mr. Townley's Theory: And so did (as their Author was pleased to tell me) some Trials made about the same time by that Noble Virtuoso and eminent Mathematician the Lord Brouncker, from whose further Enquiries into this matter, if his occasions will allow him to make them, the Curious may well hope for something very accurate.

A Table of the Rarefaction of the Air.

A | B | C | D | E
1 | 00 0/0 | Subtracted from 29¾ leaves. | 29¾ | 29¾
1 ½ | 10 ⅝ | 19 ⅛ | 19 ⅚
2 | 15 ⅜ | 14 ⅜ | 14 ⅞
3 | 20 2/8 | 9 4/8 | 9 15/12
4 | 22 ⅝ | 7 ⅛ | 7 7/16
5 | 24 ⅛ | 5 ⅝ | 5 19/20
6 | 24 ⅞ | 4 ⅞ | 4 23/24
7 | 25 4/8 | 4 2/8 | 4 ¼
8 | 26 0/0 | 3 6/8 | 3 23/32
9 | 26 ⅜ | 3 ⅜ | 3 11/36
10 | 26 6/8 | 3 0/0 | 2 39/40
12 | 27 ⅛ | 2 ⅝ | 2 23/48
14 | 27 4/8 | 2 2/8 | 2 ⅛
16 | 27 6/8 | 2 0/0 | 1 55/64
18 | 27 ⅞ | 1 ⅞ | 1 47/72
20 | 28 [...] | 1 6/8 | 1 9/80
24 | 28 2/8 | 1 4/8 | 1 23/96
28 | 28 ⅜ | 1 ⅜ | 1 1/16
32 | 28 4/8 | 1 2/8 | 0 119/128

A. The number of equal spaces at the top of the Tube, that contained the same parcel of Air.

B. The height of the Mercurial Cylinder, that together with the Spring of the included Air counterbalanced the pressure of the Atmosphere.

C. The pressure of the Atmosphere.

D. The Complement of B to C, exhibiting the pressure sustained by the included Air.

E. What that pressure should be according to the Hypothesis.

To make the Experiment of the debilitated force of expanded Air the plainer, 'twill not be amiss to note some particulars, [Page] especially touching the manner of making the Trial; which (for the reasons lately mention'd) we made on a lightsome pair of Stairs, and with a Box also lin'd with Paper to receive the Mercury that might be spilt. And in regard it would require a vast and in few places procurable quantity of Quicksilver, to imploy vessels of such kind as are ordinary in the Torricellian Experiment, we made use of a Glass-Tube of about six foot long, for that being Hermetically sealed at one end, serv'd out turn as well as if we could have made the Experiment in a Tub or Pond of seventy Inches deep.

Secondly, We also provided a slender Glass-Pipe of about the bigness of a Swans Quill, and open at both ends: All along which was pasted a narrow list of Paper divided into Inches and half quarters.

Thirdly, This slender Pipe being thrust down into the greater Tube almost fill'd with Quicksilver, the Glass helpt to make it swell to the top of the Tube, and the Quicksilver getting in at the lower orifice of the Pipe, fill'd it up till the Mercury included in that was near about a level with the surface of the surrounding Mercury in the Tube.

Fourthly, there being, as near as we could guess, little more than an Inch of the slender Pipe left above the surface of the restagnant Mercury, and consequently unfill'd therewith, the prominent orifice was carefully clos'd with sealing Wax melted; after which the Pipe was let alone for a while, that the Air dilated a little by the heat of the Wax, might upon refrigeration be reduc'd to its wonted density. And then we observ'd by the help of the above-mentioned list of Paper, whether we had not included somewhat more or somewhat less than an Inch of Air, and in either case we were fain to rectifie the error by a small hole made (with a heated Pin) in the Wax, and afterwards clos'd up again.

Fifthly, Having thus included a just Inch of Air, we lifted up the slender Pipe by degrees, till the Air was dilated to an Inch, an Inch and an half, two Inches, &c. and observed in Inches and Eighths, the length of the Mercurial Cylinder, [Page] which at each degree of the Air's expansion was impell'd above the surface of the restagnant Mercury in the Tube.

Sixthly, The Observations being ended, we presently made the Torricellian Experiment with the above-mention'd great Tube of six foot long, that we might know the height of the Mercurial Cylinder, for that particular day and hour; which height we found to be 29¾ Inches.

Seventhly, Our Observations made after this manner furnish'd us with the preceding Table, in which there would not probably have been found the difference here set down betwixt the force of the Air when expanded to double its former dimensions, and what that force should have been precisely according to the Theory, but that the included Inch of Air receiv'd some little accession during the Trial; which this newly-mention'd difference making us suspect, we found by replunging the Pipe into the Quicksilver, that the included Air had gain'd about half an eighth, which we guest to have come from some little Aëreal bubbles in the Quicksilver, contain'd in the Pipe (so easie is it in such nice Experiments to miss of exactness.) We try'd also with 12 Inches of Air shut up to be dilated; but being then hindred by some unwelcome avocations to prosecute those Experiments, we shall elsewhere, out of other Notes and Trials (God permitting) set down some other accurate Tables concerning this matter. By which possibly we may be assisted to resolve whether the Atmosphere should be look'd upon (as it usually is) as a limited and bounded Portion of the Air; or whether we should in a stricter sense than we did before, use the Atmosphere and Aëreal part of the World for almost equivalent terms; or else whether we should allow the word Atmosphere some other notion in relation to its Extent and Limits; (for as to its Spring and Weight, these Experiments do not question, but evince them.) But we are willing, as we said, to refer these matters to our Appendix, and till then to retain our wonted manner of speaking of the Air and Atmosphere. In the mean time (to return to our last-mention'd Experiments) besides that so little a variation may be in great [Page] part imputed to the difficulty of making Experiments of this nature exactly, and perhaps a good part of it to something of inequality in the cavity of the Pipe, or even in the thickness of the Glass; besides this, I say, the proportion betwixt the several pressures of the included Air undilated and expanded, especially when the Dilatation was great (for when the Air swell'd but to four times its first extent, the Mercurial Cylinder, though of near 23 Inches, differ'd not a quarter of an Inch from what it should have been according to Mathematical exactness) the proportion, I say, was sutable enough to what might be expected, to allow us to make this reflexion upon the whole, That whether or no the intimated Theory will hold exactly, (for about that, as I said above, I dare determine nothing resolutely till I have further considered the matter) yet since the Inch of Air when it was first included was shut up with no other pressure than that which it had from the weight of the incumbent Air, and was no more comprest than the rest of the Air we breathed and moved in; and since also this Inch of Air, when expanded to twice its former dimensions, was able with the help of a Mercurial Cylinder of about 15 Inches to counterpoise the weight of the Atmosphere, which the weight of the external Air gravitating upon the restagnant Mercury was able to impell up into the Pipe, and sustain above twenty eight Inches of Mercury when the internal Air by its great expansion had its Spring too far debilitated to make any considerable (I say considerable, for it was not yet so dilated as not to make some) resistance: Since, I say, these things are so, the free Air here below appears to be almost as strongly comprest by the weight of the incumbent Air as it would be by the Weight of a Mercurial Cylinder of twenty eight or thirty Inches; and consequently is not in such a state of laxity and freedom as men are wont to imagine; and acts like some mechanical Agent, the decrement of whose force holds a stricter proportion to its increase of dimension, than has been hitherto taken notice of.

[Page]I must not now stand to propose the several reflexions that may be made upon the foregoing Observations touching the Compression and Expansion of Air; partly because we could scarce avoid making the Historical part somewhat prolix; and partly because I suppose we have already said enough to shew what was intended, namely, that to solve the Phaenomena there is not of our Adversaries Hypothesis any need: the evincing of which will appear to be of no small moment in our present Controversie, to him that considers, that the two main things that induced the Learned Examiner to reject our Hypothesis are, that Nature abhors a Vacuum, and that though the Air have some Weight and Spring, yet these are insufficient to make out the known Phaenomena; for which we must therefore have recourse to his Funiculus. Now as we have formerly seen, that he has not so satisfactorily disproved as resolutely rejected a Vacuum, so we have now manifested that the Spring of the Air may suffice to perform greater things than what our Explication of the Torricellian Experiments and those of our Engine obliges us to ascribe to it. Wherefore since besides the several difficulties that incumber the Hypothesis we oppose, and especially its being scarce, if at all, intelligible, we can add that it is unnecessary; we dare expect that such Readers as are not byass'd by their reverence for Aristotle or the Peripatetick Schools, will hardly reject an Hypothesis which, besides that it is very intelligible, is now prov'd to be sufficient, only to imbrace a Doctrine that supposes such a rarefaction and condensation, as many famous Naturalists rejected for its not being comprehensible, even when they knew of no other way (that was probable) of solving the Phaenomena wont to be explicated by it.

[Page]

The III. Part. Wherein what is objected against Mr. Boyle's Explications of particular Experiments, is answered.

AND now we are come to the third and last Part of our Defence; wherein we are to consider what our Examiner is pleas'd to object against some passages of our Physico-Mechanical Treatise. But though this may seem the only part wherein I am particularly concern'd; yet perhaps we shall find it, if not the shortest, at least the easiest, part of our Task. Partly, because our Author takes no exceptions at the Experiments themselves, as we have recorded them (which from an Adversary, who in some places speaks of them as an Eye-witness, is no contemptible testimony that the matters of fact have been rightly delivered:) and partly, because there are divers Experiments which, together with their Explications, the Examiner has thought fit to leave untoucht, and thereby allows us to do so too: and partly also, because that (as to divers of those Experiments upon which he animadverts) he does not pretend to shew that our Explications are ill deduc'd or incongruous to our Principles; but only that the Phaenomena may be explain'd either better or as well by his Hypothesis, whereof he supposes himself to have demonstrated the truth, together with the erroneousness of ours, in the other parts of his Book, especially the third, fourth and fifth Chapters. So that after what we have said to vindicate the Hypothesis we maintain, and take away our Author's imaginary Funiculus; it will not be requisite for us on such occasions to examine his particular Assertions and Explications. Which Advertisement we hope the Reader will be pleased to bear in mind, and thereby save himself and us the trouble of a great deal of unnecessary repetition. Wherefore presuming he will do so, we shall not stay to examine the first and second Corollaries, which in his [Page] 17 Chapter he annexes to the manner of emptying our Receiver by our Pump. Neither should we say any thing as to his third and last Corollary, but that we think fit to desire the Reader to take notice, that according to what he teaches in that place, the more the Air is rarefied, the more forcibly it is able to contract it self.

A defence of our 1. and 2. Experiments.

And to proceed now to his 18 Chapter, which he intitles De Experimentis Boylianis, we shall find according to what we lately noted, that against the first Experiment he objects nothing save that, if one of the Fingers be applied to the Orifice of the Valve when the Pump is freed from Air, the Experimenter shall feel to his pain that the Sucker is not thrust inward by the external Air, but, as the Finger, drawn inward by the internal. But this Phaenomenon of the intrusion of the Finger into a Cavity, where it finds no resistance, having been formerly accounted for according to our Hypothesis, we shall not need to repeat our Explication of it; though this mistaken Phaenomenon supplies our Adversary with divers of his following Animadversions, and indeed with a great part of his Book. And accordingly his Objection against our Second Experiment being of the same nature with that against the first, requires but the same Answer: For it will not alter the case that he adds upon this Experiment, Hoc esse discrimen manifestum inter pressionem & suctionem, quod suctio efficiat hujusmodi adhaesionem, pressio autem minimè; since to say so is but to affirm, not to prove.

The 3. Experiment.

What our Author would except against the 3. Experiment he ought to have more intelligibly exprest: For whereas of a Discourse wherein I deliver several particulars, he only says that Nullatenus satisfacit, ut legenti constabit; I would not do the Reader the injury to suspect him of taking this proofless Assertion for a rational Confutation; especially since upon the review [Page] of that third Experiment I find nothing that agrees not with my Hypothesis, however it may disagree with the Examiners. But, to consider the Explication he substitutes in the room of our Doctrine, which he rejects, he gives it us in these words; Hoc quo (que) Experimentum principiis nostris optimè convenit: Cum enim per illam Emboli depressionem aër in cavitate brachii inclusus separetur ab eodem brachio, descendat (que) simul cum Embolo (uti de aqua simul cum argento vivo descendente capite decimo tertio vidimus) fit ut in tota illa depressione, novae semper ab aëre illo descendente superficies deripiantur simul & extendantur, ut ibidem de aqua est explicatum: cum ita (que) aeque facile diripiantur & extendantur hujusmodi superficies in fine depressionis ac initio, mirum non est quod eadem utrobi (que) sentiatur deprimendi difficultas.

By which though he seems to intend an Opposition to that part of the third Experiment which I oppos'd not against his Opinion, but that of some learned Vacuists: Yet (not to mention that he seems to have somewhat mistaken my sense) he offers nothing at all to invalidate my inference against them; but instead of that proposes a defence of his own Opinion, which supposes the truth of his disproved Hypothesis, and is either unsatisfactory even according to that, or else disagrees with what himself hath taught us but a little before. For 'tis evident that the more the Sucker is depress'd, the more the Cylinder is exhausted of Air. And in his third Corollary (which we lately desired the Reader to observe) speaking of the Air in the Receiver (and the case is the same with the Air in the Cylinder) he affirms more than once, Eo magis extendi ac rarefieri aërem relictum, quo plus inde exhauritur, majoremque proinde acquirere vim sese contrahendi. Whereas here he would have us believe, that the little internal Air that was in the Cavity of the shank of the Stop-cock, does as strongly retract the Sucker, or, which in our case is all one, resist its depression, when the Sucker is yet near the top of the Cylinder, (and consequently when the included Air is but a little dilated) as when the same Sucker being forced down to the lower part of the [Page] Cylinder, the same portion of remaining Air must be exceedingly more distended.

The 4. Experiment.

In the Fourth Experiment, touching the swelling of a Bladder upon the removal of the ambient Air; and proportionably to that removal: Our Author objects nothing against the Explication we give of it by the Spring of the Air included in the Bladder, and distending it according as the pressure of the ambient Air is weakned. But he endeavours also to explicate it his way, to which he says this circumstance does excellently agree, that upon the regress of the external Air into the Receiver, the tumid Bladder immediately shrinks, because (saith he) by such ingress of the external Air, the Air in the Receiver, which drew the sides of the Bladder outward from the middle of it, is relax'd. Which Explication whether it be more natural than ours (that ascribes the shrinking of the Bladder to the pressure of the Air that is let into the Receiver) let the Reader judge, who has considered what we have formerly objected against the Examiners Funiculus, and the Relaxation of it upon the admission of Air.

As for the reason likewise he adds, why a perforated Bladder does not also swell, namely, that by the hole, how little soever, the included Air is suck'd out by the rarefi'd ambient, we leave it to the impartial Reader to consider whether is the more genuine Explication, either ours (against which he has nothing to object) or his, which to make clearly out he ought (according to what we formerly noted disputing against his Funiculus) to shew us what kind of strings they are; which though, according to him, strongly fastned to the inside of the Receiver and the superficies of the Bladder, must draw just as forcibly one as another, how long soever they be without the Bladder in comparison of those that within the Bladder draw so as to hinder the diduction of its sides. For Experience shews, that in a perforated Bladder the wrinkles continue as if there were no drawing at all.

[Page]And though he could describe how such a string may be context, yet our Explication will have this advantage in point of probability above his, That whereas he denies not that the Air has Spring and Weight, as we deny his Funiculus to have any other than an imaginary existence; and whereas he acknowledges that by the Instrument the Air about the Bladder is exhausted; to shew that there needs no more than that, and consequently no Funiculus, to draw asunder the sides of the Bladder, we can confirm our Explication by the formerlymentioned Experiment of the ingenious Paschal, who carrying a flaccid Foot-ball from the bottom to the top of an high Mountain, found it to swell proportionably as he ascended, and as the weight and pressure of the ambient Air decreased, and likewise to shrink again as he descended. And yet in this case there is no recourse to be had to a Funiculus of violently-rarefi'd Air to draw asunder every way the sides of the Foot-ball. But however the Examiner will be able to defend his Explication, it may suffice us that he has objected nothing against ours.

The 5. Experiment.

Against the cause we assign of the fifth Experiment he likewise objects nothing, but only ascribes the breaking of the Bladder to the self-contraction of the rarefi'd Air in the Receiver. And therefore referring the Reader to what we have newly said about the last Experiment, we will with our Author pass over the sixth and seventh, to which he has no quarrel, and proceed to the eighth.

The 8. Experiment.

This is that wherein we mention our having broke a GlassReceiver, which was not globular, by the exhaustion of most of the inward Air, whereby its debilitated pressure became unable to resist the unweakned pressure of the outward Air. But this Explication the Examiner confidently rejects in these words, At profect non videtur credibile, mollissimum hunc aërem tam vehementer[Page]vitrum (tantae praesertim crassitudinis quantae ibidem dicitur) undi (que) sic comprimere ut illud perfringat: as if it were more credible that the little Air within (which, according to him, is so much thinner than common Air) should be able to act more powerfully upon the Glass than the Air without, which himself confesses to be a heavy body, and which not only reaches from the surface of the Earth to the top of the highest Mountains, but which (as may not improbably be argued from what we have elsewhere delivered) may, for ought we know to the contrary, be heaped upon the Receiver to the height of some hundreds of Miles, nay, to I know not how many thousands, in case the Atmosphere See Part 2. C. 5. be not a bounded portion of the Air, but reach as high as It.

As for the Explication he substitutes in these words, Verius ita (que) respondetur, ideo sic fractum esse illud vitrum, quia per exhaustionem illam later a ejus vehementiùs introrsum sint attracta, quam ut (ob figuram illam resistendo minus idoneam) resistere potuerint. Cum enim inclusus aër lateribus vitri firmissimè adhaereat, nihil aliud erit aërem illum sic exhaurire, quam satagere latera vitri introrsum flectere: By what we have already discoursed about the Funiculus, the Reader may easily discern what is to be answered. Nor does our Author here shew us any way by which his imaginary strings should take such fast hold of the sides of the Glass, as to be able to draw them together notwithstanding the resistance they find from the close texture of the Body to be broken.

The 9. Experiment.

Our Explication of the ninth Experiment he handles very severely: for having briefly recited it, he proposes his Objection against it thus, Sed profecto nimis longè videtur hoc à veritate recedere: potest (que) vel inde solum satis refutari; quia si tanta sit pressura aëris sic per tubum illum in phialam descendentis, ut ipsam phialam perfringat, deberet profecto inclusam aquam, cui immergitur[Page]ille tubus, valde quo (que) ante fractionem phialae commovere, bullulas (que) in eadem excitare, &c. ut constat, siquis, insufflando per illum tubulum, aquam vel mediocriter sic premat. At certum est aquam, antequam frangatur sic phiala, nec tantillum moveri: ut experienti constabit.

But, I do confess, I do for all this think our Explication more true, than well considered by our Author. For the putting of water into the Vial that was broken, was done (as is clearly intimated in the beginning of our Narrative) upon a particular design (as indeed we tryed divers other things with our Engine, not so much with immediate reference to the Spring of the Air, as to make use of such Tryals in some other of our Writings.) And accordingly in the second Tryal mentioned in the same Experiment the water was omitted. But, notwithstanding this water, the sides of the Glass being exposed to the pressure of the Atmosphere, had that whole pressure against them before the exhaustion of the Receiver; so that there needed no such blowing in of the Air afresh as our Author imagines, to effect the breaking of the Vial, it being sufficient for that purpose, that the pressure against the convex superficies of it was taken off by the exhaustion of the Receiver, the pressure against the concave superficies remaining as great as ever. And therefore we need not altogether deny what the Examiner sayes that Licet clausus superne fuisset tubulus ille, eodem tamen modo fract a sine dubio fuisset phiala. For, since in such cases the Air (as we have often taught) is shut up with the whole pressure of the Atmosphere upon it, it may almost as easily break the Glass as if it were unstopt. And accordingly we mention in the 36. Experiment the breaking of a thin Glass Hermetically seal'd upon the recess of the ambient Air. But, how confidently soever our Author speaks, I thought fit to adde the word almost, because we observed in the 39 Experiment, that such thin Vials (and thick ones will not break) are subject upon the withdrawing of the ambient, Air to retch a little, whereby the Spring of the Air within the Vial might in some cases (I say, in some) be so far weakned as not to be able to break it, unless [Page] assisted by the pressure of the Atmosphere wherewith it communicates, and which leans upon it. And when the Vial does actually begin to break, then the pursuing pressure of the outward Air upon the yielding Air within the Vial may help to throw the parts of the Glass more forcibly asunder.

All the Experiments from the 9. to the 17. exclusively our Examiner leaving uncensured, we may with him advance to the consideration of the 17.

The 17 Experiment defended.

In this we relate how, when we made the Torricellian Experiment, we shut up the restagnant Mercury together with the Tube and the suspended Mercurial Cylinder (of about 29. Inches) in our Receiver, that by drawing off and letting in the Air at pleasure upon the restagnant Mercury, and consequently weakning and increasing its pressure, we might make it more clearly appear than hitherto had been done by Experiment, that the suspension of the Mercurial Cylinder, and the height of it, depended upon the greater or lesser pressure of the Air. But against our Explication of this Experiment (which has had the good fortune to convince and satisfie many ingenious men) the Examiner objects nothing in particular, contenting himself to have recourse here also to his Funiculus. Yet two observations of ours he is pleased to take notice of.

The first is, that though the Quicksilver were exactly shut up into our Receiver after the manner newly declared, yet the suspended Quicksilver did not descend: whence having said that I argue, that it is now sustained not by the Counterpoise of the Atmosphere, but by the Spring of the Air shut up in the Receiver, he subjoyns onely this, Sed rectius sane infertur, Cylindrum illum nihil ibidem antea praestitisse. But whether this be not gratis dictum we leave the Reader to collect from what we have formerly discourst in the second Part of this Defence of the Spring of the Air; especially from that Experiment; by which it appears, that Spring may sustain a far higher Cylinder of Quicksilver.

[Page]In the second Observation he mentions of ours, he summarily recites our Explication of the descent and ascent of the Mercury in the Tube, by the debilitated and strengthned Spring of the Air. But without finding fault with our application of that principle to the Phaenomena, he sayes that he has sufficiently refuted the principle it self in the fourth Chapter, (which how well he has done we have already seen) and therefore explicates the matter thus; Dico igitur (sayes he) argentum per illam exhaustionem sic in tubo descendere, quod deorsum trahatur ab aëre qui incumbit argento restagnanti: siquidem incumbens ille aër jam per exhaustionem valde rarefact us & extensus, sese vehementer contrahit, & contrahendo conatur etiam subjectum sibi argentum restagnans è suo vasculo elevare, unde fit ut (argento illo restagnante minus. jam gravitante in fundum sui vasculi) argentum quod est in tubo descendat; ut per se patet. Adeo (que) mirum non est, quod, ingrediente postea aëre externo, rursum argentum ascendat, cum per illum ingressum vis illa sic elevans argentum restagnans debilitetur. But this Explication supposing such a Funiculus as we have already shewn to be but fictitious, the Reader will easily gather what is to be judged of it from what has been already delivered. Wherefore I shall onely subjoyn, that by this Explication, were it admitted, there is onely an account given of that part of our seventeenth Experiment which relates to the descent of the Mercury below its wonted height, and its re-ascent to it. But as for our having by the forcing in some more Air into the Receiver, impell'd the Quicksilver to a considerably-greater height than 'tis wont to be sustain'd at in the Torricellian Experiment, I confess I understand not how the Examiner gives an account of it in the following words, (which are immediately annex'd to those we last recited of his, and which are all that he employes to explicate this notable Phaenomenon) At (que) hinc etiam redditur ratio alterius quod ibidem quo (que) notatur, nempe quod per violentam intrusionem aëris externi in Recipientem, ascenderit argentum notabiliter supra digitos 29½. Nam sicut per extractionem aëris argentum infra stationem detrahitur, sic etiam per intrusionem [Page]novi supra eandem elevabitur. For in this passage I see not how he himself does not rather repeat the matter of fact, than give any account how it is perform'd. And if it be alledged on his behalf, That according to his principles it may be said that, upon the pressure of adventitious Air upon the restagnant Mercury, the Funiculus in the Tube, that was not able before to draw it up above 29½ Inches, is now enabled to draw it up higher; I demand upon what account this new Air does thus press against the restagnant Mercury, and impell up and sustain that in the Tube. It will not be said that 'tis by its weight; for as much Mercury as may be thus impell'd up above the usual station will weigh a great many times more than the Air forc'd into the Receiver. And therefore it remains that the additional Air counterpoises the additional Mercury by its Spring. And if we consider withall, that there's no reason to doubt, (especially considering what we have formerly delivered upon tryal touching the power of comprest Air to impell up Quicksilver) but that, had we not been afraid of breaking our Vessel we might by forcing more Air into the Receiver have impell'd it up to the top of the Tube, and kept it there; we shall scarce deny but that, supposing there could be no such Funiculus as our Examiner's in rerum natura, the pressure of the incumbent Air alone might suffice to keep a correspondent Cylinder of Mercury suspended: and that without any attraction of the restagnant Mercury by a Funiculus of violently-distended Air in the Receiver, the Quicksilver in the Tube may be made to rest at any height greater or lesser, provided it exceed 30 Inches, onely because its weight is just able to counterbalance the pressure of the contiguous Air.

I know not whether I may not adde (to express an unwillingness to omit what some may think proper to do my Adversary right) that it may be said for the Examiner, that he in the 11 page acknowledging with us a power in the Air to recover its due extension if it be crouded into less room than its disposition requires; a man may from that principle solve the Phaenomena in question by saying, that the Air in the Receiver [Page] being forcibly comprest by the intrusion of fresh Air into the same vessel, does by its endeavour to recover its due expansion press upon the restagnant Mercury, and force up some of it into the Tube. But this Explication, though it agree with what the Author teaches in a place very distant from his Notes upon our 17 Experiment, now under debate; yet still 'tis not clear to me how, by what he sayes in these Notes, the Phaenomenon is accounted for as the word Hinc imports it to be. But otherwise I need not quarrel with the Explication, since without recurring to the Funiculus for the sustaining of the additional Mercury, the solution of the Phaenomenon is given upon the same principle that I employ.

The 18 Experiment.

Our Examiner in his Animadversion upon the 18 Experiment, having recited my Conjecture as the cause why a Cylinder of Mercury did in Winter rise and fall in the Tube, sometimes as Water is wont to do in a Weather-glass, according to the laws of heat and cold, and sometimes quite contrary thereunto; adds, that this Experiment does strongly enough overthrow our Hypothesis of the Atmospherical Cylinder, and clearly shew that the Quicksilver is not sustained by it: Nam (sayes he) si hic ab eo sustentatum fuisset, debuisset potius frigidiore tempore ascendere quam descendere, eo quod aër tunc multo densior esset & gravior. Ita (que) non sustentatur argentum ab aëris aequipondio, ut asseritur. And by the same Argument he concludes against the Mercury's being sustained by the Spring of the Air. But in his Animadversions upon this Experiment he seems to have been too forward to reprehend; for he neither well confutes my Conjecture, nor substitutes so much as a plausible one in the stead of it. And as to his Objection I answer,

First, That it doth not conclude: because that as sometimes the Quicksilver in the Tube did rise in warmer, and fall in colder, weather; so at other times it did rather emulate the ascent and descent of water in a Weather-glass.

[Page]Secondly, Though it be true, that Cold is wont to condense this or that parcel of Air, and that a parcel of Air may be made heavier by Condensation; yet that is in regard of the ambient Air that retains its wonted laxity, in which the condensed Air is weighed. But our Author has not yet proved, that in case the cold of the Winter should condense the whole incumbent Atmosphere, it would then gravitate sensibly more upon the restagnant Quicksilver than before. As a Pound of Wooll will not sensibly vary its weight, though the hairs whereof it is composed be made to lie sometimes in a looser, sometimes in a closer, order.

And, thirdly, this Objection does as little agree with his Doctrine as with my Conjecture: For in the 50. page, where he gives us an account according to his principles of the rising and falling of water in a Weather-glass, and compares it with the suspension of Quicksilver, he tells us, Hinc fit quod, contracto hoc funiculo per frigus, aqua illa tempore frigido ascendat, descendat autem tempore calido, eo quod per calorem funiculus ille dilatetur. So that, according to the Examiner himself, the Quicksilver ought to have ascended in colder, and descended in warmer, weather. Now, although I proposed my thoughts of the difficult Phaenomenon under consideration but as a Conjecture, and therefore shall be ready to alter them, either upon further discovery, or better information; yet I see not why it should be post-posed to the Examiner's, who, though he rejects our Explication, substitutes no other than what may be gathered from these words, Ego certe non dubito quin dentur hujusmodi occultae causae, quibus funiculus ille subtilis, quo in tubo suspenditur argentum (ut dictum est capite decimo) modo producatur, modo abbrevietur, &c. sic (que) argentum nunc demittat, nunc elevet. For, since we have made it probable that the copious Fumes sometimes suddenly ascending into the Air, and rolling up and down in it, sometimes sensibly altering (if good Authors may be credited) the refraction of it, and since some other causes, mentioned in our eighteenth Experiment, may alter the density and gravity of the Air that leans upon the restagnant Mercury; I [Page] suppose the Reader will think it more intelligible, and probable that alterations, other than those produced by heat and cold may happen to the incumbent Atmosphere, which freely communicates with the neighbouring Air, and may thereby become sometimes more stufft, and sometimes more destitute of adventitious Exhalations; than that such changes should happen to a Funiculus included in Glass, which according to our Author is impervious to the subtilest steams that are, and concerning which he offers not so much as a Conjecture upon what other account it can happen to be sometimes contracted, and sometimes stretch'd.

The 19 Experiment.

Upon this the Examiner has onely this short Animadversion, In decimo nono ostendit aquam eodem modo per exhaustionem Recipientis descendere, quo in praecedente descendere ostenderat argentum vivum; cujus cum eadem sit ratio, non est cur amplius ei insistamus. In which words since he offers nothing new or peculiar to shew any incongruity in our Explication to our principles, which agree very well with the new Phaenomena of the Experiment; we are content to leave the Reader to judge of the Hypotheses themselves, which of the two is the more probable, either ours, that onely requires that the Air in the Receiver should equally resist a Cylinder of Water and of Quicksilver, when their weight is but the same, though their altitudes be not; or the Examiner's, which exacts that (according to what we formerly elsewhere noted) Bodies of such differing nature and texture as Quicksilver and Water should need but just the same weight or strength to rarefie them into a Funiculus.

The 20 Experiment.

In his Examen of this Experiment our Author makes me infer from the Phaenomena he repeats, that not onely the Air, but the Water also has a Spring. But though I suspect not that he does wilfully mistake my sense, yet by what I write in this and the following Experiments the Reader may well enough [Page] perceive, that I spoke but very doubtfully of a Spring in the water; nay, and that I did in the 154 page expresly teach, That the intumescence of it might (at least in great part) proceed from that of the small parcels of Air, which I thought to be usually harboured in the body of that liquor.

But whereas I ascribe the appearance of the Bubbles in the water to this, that upon the exhaustion of some of the Air incumbent on the water, the pressure of what remains is much debilitated, whereby the little Particles of Air lurking in the Water are allowed to expand themselves into bubbles; he rejects this Explication as manifestly false: Nam Sed contra manifeste. (sayes he) si ita fieret, deberent profecto hujusmodi bullulae non è fundo vasis sic ascendere, (uti tam in hoc quam in sequentibus experimentis in quibus de istis bullis agitur semper asseritur) sed è superiore parte aquae, ubi minus premuntur, ut per se est manifestum. But why he should be here so peremptory I confess I do not, for all this Objection, yet see: For in the bottom of the next page he sayes, he will not deny but that Aërial Particles latitant in the other parts of the water (he had before spoken of the bottom of it) may be extended into bubbles by his way of Rarefaction. And that we particularly mentioned the rising of bubbles, even from the bottom of the water, was because that circumstance seem'd to deserve a peculiar note; and not (as he seems to imagine) as if the bubbles did not also rise from the superior parts of the liquor, since we did take notice of it about the middle of the 149 page. And we often in this and the following See also in the 43 Experim. these passages, — And this Effervescence was so great in the upper part of the water, &c. As also, — The Effervescence was confin'd to the upper part of the water, unless, &c. Experiments observ'd, that the ascending bubbles grew bigger the nearer they came to the top. Which agrees more clearly with our Hypothesis wherein their conspicuous swelling as they ascend is attributed more to the lessening of the pressure of the incumbent Air than to the decrement of the weight of the incumbent water, (since when the surface of this liquor is lean'd upon by the Atmosphere, the ascending bubbles scarce sensibly increase [Page] in Vessels no deeper than ours) then with the Explication which the Examiner gives in these words, Respondeo, aquam per illant aëris exhaustionem non sponte sic ascendere, sed sursum violenter trahi, ac elevari à rare facto illo aëre sese contrahente. Quemadmodum enim aqua aliqualem patitur compressionem (ut experientiâ constat) it a & aliqualem quo (que) hic patitur distentionem. At (que) hinc clarè patet, cur potius à fundo vasts quam à parte aquae superiore oriantur hujusmodi bullae. Cum enim vehemens illa suctio conetur aquam à fundo phialae elevare, nascitur ibidem subtilis quaedam materia quae in bullas conversa sic ascendit, uti capite decimo quinto in quarto Experimento dictum est. For, whatever he may think, it does not hence so clearly appear how the endeavour only of the Funiculus to draw up the Water from the bottom of the Vial, to which, that endeavour notwithstanding, it remains contiguous, should generate in some parts of the bottom of the Glass, and not in others, such a subtile matter as he tells us of. And I suppose the Reader will, as well as I, wish he had more intelligibly declared how this strange generation of subtile matter comes to be effected. And I presume it will likewise be expected that he also declare, why both in our case and in the Torricellian Experiment the bubbles grow so much larger by being nearer the top of the liquor; if, as he rejects our Explication of this Circumstance, the effect of the suction he speaks of be greater upon the lower part of the liquor than the upper, to which alone nevertheless his Funiculus, that is said so to draw the liquor, is contiguous.

Our Author making no particular Objection against the 10 following Experiments, we also shall pass them by, and fall with him upon the consideration of the 31 Experiment.

The 31 Experiment.

Upon this our Author having recited our Conjecture as the cause why two very flat and smooth Marbles stick so closely together, that by lifting up the uppermost you may take up also the lowermost, approves my way of examining that Conjecture. But whereas I say that the reason why, though the Marbles [Page] were kept together by the pressure of the ambient Air, yet they did not fall asunder in our exhausted Receiver, no not though a weight of 4 Ounces were hung at the lower stone, might be, that by reason of some small leak in the Receiver the Air could not be sufficiently drawn out: yet he tells us with his wonted confidence, Certum esse, sententiam illam vel hoc solo Experimento satis refelli. But possibly he would have spoken less resolutely, if he had made all the trials about the adhesion of Maibles that we relate our selves to have made in the short History we have publish'd of Fluidity and Firmness. For our Examiner speaks as if all that we ascribe to the Air in such Experiments were to sustain the lower Marble with the weight perhaps of a few Ounces: Whereas in case the Air be kept from getting in at all between the stones, it may (according to our Hypothesis) sustain a Weight either altogether or well-nigh equal to that of a pillar of Air as broad as the Basis of thelower Marble, and as long as the Atmosphere is high, or to the weight of a pillar of Quicksilver of the same thickness, and about 30 Inches long; these two pillars appearing by the Torricellian Experiment to counterpoise each other. And therefore since in the seventeenth Experiment, when we had exhausted our Receiver as far as we could, there remain'd Air enough to keep up in the Tube a Cylinder of about an Inch long of Quicksilver; and since the broader the contiguous Marbles are, the greater weight fastned to the lowermost may be sustain'd by the resistance of the Air, (as is obvious to him that considers the Hypothesis, and as we have proved by Experiment in the forementioned Tract) it need be no wonder that the Air remaining in the Receiver should be able to support the lowermost Marble, whose Diameter was near two Inches, and a weight of four Ounces, those two Weights being inferior to that of a Mercurial Cylinder of that Diameter and an Inch in length. And though it were not, yet we are not sure that the Receiver was as well emptied when we made the 31 Experiment, as when we made the 17. And (if my Memory does not much misinform me) 'twas with the same pair of Marbles that in the [Page] presence of an illustrious Assembly of Virtuosi (who were Spectators of the Experiment) the uppermost Marble drew up the lowermost, though that were clogg'd with a weight of above 430 Ounces.

As for the account the Examiner substitutes of our Phaenomenon, I know not whether many Readers will acquiesce in it: For, not to insist upon the Objection which himself takes notice of, that according to him the distended Air in the Receiver should draw asunder the adhering Marbles; his Explication supposes that there cannot naturally be a Vacuum, whence he infers that, Necesse erat ut lapis ille non aliter descenderet, quàm relinquendo post se tenuem bujusmodi substantiam, qualis ab argento vivo aut aquâ sic descendentibus relinqui solet. But whereas he adds, that the cause of the obstinate adhesion we meet with in our case is, that such a substance is far more difficult to be separated from Marble than from Qucksilver or any other kind of Body; that Assertion is precarious. And though I have tried Experiments of this nature with stones of several sizes, perhaps an hundred times, yet I never could find that by their cohesion they would sustain a weight greater than that of a Pillar of the Atmosphere that prest against the lowermost: Which is a considerable Circumstance, that much better agrees with our Explication than our Adversaries. And whereas he further says, Vnde existimo planè, si perfectè complan at a fuerint duo marmora sic conjunct a, it a ut nullus omnino aër inter utrum (que) mediaret, non posse ea ullis humanis viribus ab invicem divelli: I hope I need not tell the Reader, that whether or no this agree with what he had immediately before taught of the separableness of a subtile substance even from Marble, so bold and improbable an Assertion requires the being countenanc'd with a much better proof than the only one he subjoyns in these words, Vti etiam confirmat exemplum quod ibidem adducit Author de lamina aenea, tabulae cuidam marmoreae it a adhaerente, ut à lacertoso juvene, de suis viribus gloriante, non potuerit per annulum centro ejus affixum inde elevari. For sure there is great odds betwixt the strength of a man unassisted by any Engine, [Page] and the utmost extent of Humane Power. And indeed accor ing to our Hypothesis, and without having recourse to Natures dreading of a Vacuum, the case is clear enough: For, supposing the Plate to be of any considerable breadth, the Pillar of the Atmosphere that lean'd upon it, and must at the instant of its deserting the superficies of the Table all at once be lifted up with it, may well exceed the force of a single man, especially in an inconvenient posture; since by the cohesion of a pair of Marbles of about three Inches Diameter, I did with my own hands take up above a thousand and three hundred Ounces.

The 32 and 33 Experiments.

Against our Explication of these two, which our Author examines together, he objects nothing peculiar, but contents himself to explicate them by his Funiculus: Wherefore neither shall we need to frame any peculiar defence for it, especially if the Reader will be pleased to refer hither as much of what we oppos'd to his Animadversion on the third Experiment as is justly applicable to our present Controversie. Our Author indeed endeavours to prove his Explication by saying, that the distended Air in the exhausted Cylinder draws up the Sucker with the annexed weight, Eodem fere modo quo videmus in cueurbitulis dorso aegrotantis applicatis, in quibus, extincta jam flamma, rarefact us aër se contrahens carnem tam vehementer, uti videmus, elevat attrahit (que) intra cucurbitulam. But that Phaenomenon is easily enough explicable in our Hypothesis, by saying, that upon the vanishing of that heat which strengthned the pressure of the included Air, the Spring of it grows too weak to resist any longer the pressure of the ambient Air; which thereupon thrusts the flesh and neighbouring blood of the Patient into the Cupping-glass, almost after the same manner as we formerly taught the Pulp of the Finger to be thrust into the deserted Cavity of the Glass-Tube in the Torricellian Experiment.

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The 34, 35 and 36 Experiments.

To these our Author saying nothing but this, In his tribus nihil peculiariter occurrit hic explicandum, cujus ratio ex jam dictis non facile pateat; we also may be allow'd to pretermit them, and pass on to

The 37 Experiment.

Of the appearance of Light or Whiteness, mentioned in this Experiment, the Examiner confesses that we have assigned a cause probable enough, by referring it to the vehement and sudden commotion of the included Air. And indeed though I do still look upon some of the things that I hesitantly propos'd about this difficult Phaenomenon but as mere Conjectures, and though he annexes his Explication of it; yet I see not but that it is coincident with ours, or not better than it. For, to what I had said of the Commotion of the parts of the Air, he adds only in two or three several places their being violently distended; which how it improves the Explication of the Phaenomenon I do not readily see. And whereas he subjoyns, Existimo autem dicendum potius candorem illum esse lumen quoddam reflexum, quam innatum, eo quòd (ut testatur Author) in tenebris non appareat, sed solum de die aut accensa candela: I presume the attentive Reader will easily discern that his Opinion is much-what the same that I propos'd and grounded on the same reason. But the chief difficulty in this abstruse Phaenomenon, namely why we meet with it but sometimes, our Examiner's Explication leaves untouch'd.

The 38 and 39 Experiments.

Against these our Author makes no peculiar Objections.

The 40 and 41 Experiments.

But in his Animadversions upon these, having told the Reader that I seem to ascribe the sudden extinction of the included Animals to the excessive thinness of the Air remaining [Page] in the Receiver, made by the recess of what was drawn out, unfit for Respiration; he adds resolutely enough, Verum impossible videtur, ut hujusmodi animalcula ob solum defectum crassioris aëris tam cito moriantur: But gives no other reason than that they dye so soon, which is no more than what he said in the newly-cited words, and besides is grounded upon something of mistake. For the Creatures he mentions were a Bee, a Fly, and a Caterpillar, and those included too in a small Receiver, which could be suddenly exhausted: and these indeed became moveless within a minute of an hour; but that minute was not (as the word is often us'd to signifie in English) a Moment, but the Sixtieth part of an Hour. And though these Insects did in so short a time grow moveless, yet they were not so soon kill'd; as appears by the Narrative. The sanguineous Animals that did indeed dye, were kill'd more slowly. And I remember that having purposely enquir'd of a man (us'd to go under water by the help of an Engine wherein he could carry Air with him to the bottom of the Sea) how long he could endure, before he was accustomed to dive, without breathing or the use of a Spunge; See more concerning this Objection in the Answer to it as 'tis propos'd by Mr. Hobbs. he told me, that at first he could hold out about two or three Minutes at a time: Which made me think that Divers become able to continue under Water so long, either by a peculiarly-convenient Constitution of body, or by a gradual exercise. And I am apt to think that he did, as men are wont to do, when he said two or three Minutes, mean what is indeed a much shorter time than that when exactly measured amounts to. For, having purposely made trial upon a couple of Moles that were brought me together alive, one of them included in a small, though not very small, Receiver was between two and three Minutes in killing; whereas the other being immediately after detain'd under Water did not there continue full a Minute and a quarter, before it finally ceas'd from giving any sign at all of life. By which trial it may appear, that 'tis not impossible that the want of Respiration should dispatch an Animal in as little [Page] time as is mentioned in the Experiment I am now defending. And indeed our Author either should have proved that 'tis not possible for the want of Air to destroy Animals so soon, or should have given us some better account of the Phaenomenon. For whereas he teaches us, that according to his Doctrine the little Animals above mentioned were so soon kill'd, quia per rarefactumillum aërem sese contrahentem extractus sit corum halitus: I see not that hereby, if he explicate the Phaenomenon otherwise than we, he explains it better; for he seems to speak as if he thought this halitus to be some peculiar part of the Animal in which his life resides. And besides he seems not to consider, that whereas, according to me as well as according to him, the Air contained in the Lungs (supposing these Animalcula have any) must in great part pass thence into the Receiver, (for whether that be done by the Spring of the Air it self, that was harboured in the Lungs, or the traction of the more rarefi'd Air in the Receiver, is not material in our present case) the Examiner must, as well as I, render a reason why the extenuation or recess of the halitus should cause the hasty death of the included Animals; and condemning my Conjecture he ought to have substituted another reason: and though he subjoyns these words, and concludes with them, At (que) hinc quo (que) ortae sunt vehementes illae convulsiones, quas ante mortem passas esse aviculas quasdam memorat ibidem Author; yet I doubt not but the Reader will think it had not been amiss that the Author had more intelligibly reduc'd these Tragick Symptoms from his Assumption, for the sake of those that are not Anatomists and Physicians enough to discern how his Funiculus could produce these effects.

For my part, as in the 41 Experiment I tender'd my thoughts concerning Respiration but doubtingly, so I am yet unwilling to determine resolvedly in a matter of that difficulty.

The 42 and 43 Experiments.

In his Examen of these two last of our Physico-Mechanical Experiments, the Author contents himself to endeavour to explicate [Page] the Phaenomena recited in them by the contraction of the rarefi'd Air; which, according to him, endeavours to draw up the subjacent water out of the Vial, whereby it vehemently distends the parts of that water, as he taught in the like case upon the 20 Experiment. But since we have already consider'd his Animadversion upon that, although this presumed distension of the water is not visible that we have observ'd, when cold water, that has been first freed from his interspers'd Air, is put into the Receiver, notwithstanding that the Funiculus should in that case also distend it; we are so afraid of tiring out the Readers patience by the frequent repetition of the same things, that we will leave it to him to judge which of the two Explications, the Examiner's or ours, is to be preferred, without troubling him and our selves with defence of Accounts against which our Adversary does not here make any peculiar Objections.

And thus have we by God's assistance considered what the Examiner hath been pleased to oppose either against our particular Explications, or against the Hypotheses that divers of them suppose: Wherein I have been the more particular and prolix, because I would willingly excuse my self and others from the trouble of any more Disputes of this kind. I hope there is not in my Answers any thing of Asperity to be met with; for I have no quarrel to the Person of the Author, or his just reputation; nor did I intend to use any more freedom of Speech in the answering his Objections, than his resolute way of proposing divers of them made it on those occasions needfull for the Caution of those Readers who are not acquainted with our differing ways of writing, and perhaps have not observed that some men are wont to consider as much what they propose but with a Perhaps, or some such expression of diffidence, as others do what they deliver far more resolutely. And though being very far from being wedded to my Opinions, I am still ready to exchange them for better, if they shall be duly made out to me, (which I think it possible enough they may hereafter be;) yet peradventure the Reader will think with me, that the Examiner [Page] has not given me cause to renounce any of them, since the Objections he has propos'd against me have been sufficiently answered, and since the Hypothesis he would substitute in the room of ours (besides that it is partly precarious) supposes things which divers of the eminentest Wits of our Age (otherwise of differing Opinions) profess they cannot admit or so much as understand: Whereas the Weight and Spring of the Air are not denied by our Author himself, and are demonstrable by Experiments that are not controverted betwixt us. Which things I represent for the defence of what I think the Truth, and not to offend my learned Adversary, who shall have my free consent to be thought to have fail'd rather in the Choice than in the Management of the Controversie. Though since this passes for his first Book, and since consequently he is not like to have been provoked, or engaged in point of Reputation, to challenge me or any of those far more eminent Persons he has nam'd among his Adversaries, I am induc'd by the severity wherewith I have known eminent Virtuosi speak of his Attempts, and particularly of his Funiculus, to fear that some of those he has needlesly oppos'd, will be apt to apply to him that of St. Austin against some of his Adversaries, that had disputed against him with much more Subtilty than Reason, In mala causa non possunt aliter, at malam causam quis eos coegit habere? But this notwithstanding I am, as I was going to say, content my Adversary should be thought to have said for his Principles as much as the Subject will bear; nor would I have it made his Disparagement, that I have declared that his whole Book has not made me depart from any of my Opinions or Explications, since his Hypothesis and mine being inconsistent, it may be looked upon as a sign rather that each of us have, than that either of us have not, reason'd closely to his own Principles, that the things we infer from our contrary Suppositions do so generally disagree.

FINIS.

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AN EXPLICATION OF RAREFACTION.

THE chief Arguments of the Author of a certain Treatise De Corporum inseparabilitate, whereby he endeavours to invalidate the Hypothesis of the Weight and Spring of the Air, and to set up and establish instead thereof an unintelligible Hypothesis of Attraction, performed by I know not what strange imaginary Funiculus, are only Five, two against the former, and three for the later. The first of which is, That the Weight and Spring of the Air are not sufficient to perform the Effects ascribed to them: The second, that could they be performed by that Hypothesis granted, yet the way of this strange Spring it self is not intelligibly explained or explicable by the Defenders of it. Now the former of these being little else but a bare Affirmation, and the later bearing some shew of Demonstration, I shall endeavour to examine it as I find it set down in his 20, 21, 22, 23 and 24 Chapters, to which (especially the 23) he very often in his Book refers the Reader for satisfaction, pretending there to evince that Rarefaction cannot be made out any otherwise than by supposing a body to be in 2, 3, 4, 10, 100, 1000, 1000000 of places at the same instant, and adequately to fill all and every one of those places.

First therefore, we will examine his Negative, and next his Affirmative, Arguments for this strange Hypothesis.

His Negative I find in the 20 Chapter, where he endeavours to confute the two ways of explicating the Rarefaction and Spring of the Air, namely, that of the Vacuists and that of the Plenists.

Concerning the first of these we find him conclude it impossible, [Page] first, because he had before proved that there can be no Vacuum, which being done by a Circle (viz. There is no Vacuum in the Tube because Nature abhors a Vacuum, and we see Nature abhors a Vacuum because she will not suffer a Vacuum in the Tube above the Mercury, but to prevent it will continually spin the Quicksilver into superficies, and never diminish the body of it) will suffer me to pass to his next, which is, That this way is false, because in the Experiment of the Carp's Bladder the Air is rarefi'd a 1000 times bigger; nay, in respect of the body of Gold it has 1000000 times less matter in equal spaces. And this, says he, is a Phaenomenon that is impossible ever to be made out by interspers'd Vacuities. Now that the Vacuists cannot presently, by so bold an assertion as this, be made to forsake their Principles, he may perceive by these following Solutions which I shall give of all the Phaenomena he recites, flowing naturally from an Hypothesis that I shall for the present assume. Let us suppose then the Particles of Bodies, at least those of the Air, to be of the form of a piece of Ribond, that is, to be very long, slender, thin and flexible laminae, coyled or wound up together as a Cable, piece of Ribond, Spring of a Watch, Hoop, or the like, are: We will suppose these to have all of them the same length, but some to have a stronger, others a weaker Spring: We will further suppose each of these so coyled up to have such an innate circular motion, as that thereby they may describe a Sphere equal in Diameter to their own, much after the manner that a Meridian turn'd about the Poles of a Globe will describe by its revolution a Sphere of the same Diameter with its own in the Air. By this Circular motion the parts of the laminae endeavouring to recede from the Centre or Axis of their motion, acquire a Springiness outward like that of a Watch-Spring, and would naturally flie abroad until they were stretch'd out at length, but that being incompast with the like on every side, they cannot do it without the removal of them, as not having room sufficient for such a motion. And the faster this circular motion is, the more do the parts endeavour to recede [Page] from the Axis, and consequently the stronger is their Spring or endeavour outward. These springy Bodies thus shap'd and thus moved are sufficient to produce all the Phaenomena he names as impossible to be explicated. And, first, for the business of Expansion, it will very naturally be explained by it: As let us suppose for instance the Diameter of these small coyled Particles of the Air (which being next the Earth are press'd upon by all those numerous incumbent Particles that make up the Atmosphere, and are thereby so crouded that they can but very little untwist themselves; let us suppose, I say, the Diameter of these Particles) to be 1/1000000000000 of an Inch; and then to be much of the form of those represented in the 4 Figure by ABCD: and that these Particles, when a considerable quantity of the pressure of the ambient parts is taken away, will flie abroad into a Coyle or Zone ten times as big in Diameter as before; that is, they will now be 10/1000000000000 of an Inch in Diameter, and appear in the form of those in the Figure exprest by EFGH: these Zones whirl'd round as the former will describe a Sphere 1000 times as big in bulk, and thereby fence that space from being entred by any of the like Zones: this it would doe, supposing. those Spheres did immediately always touch each other; but because of their circular motion, whenever they meet they must necessarily be beaten, and flie off from one another, and so require a yet greater space to perform their motion in. This suppos'd, there are no Phaenomena of Rarefaction (which is enough at present to answer what he objects) but may be naturally and intelligibly made out. As first, for that of the swelling of a Carp's Bladder, if we suppose some small parcels of the former comprest laminae to lie latitant within the folds of it, and being much coyled up together scarce to take any sensible room, this Bladder in the Air will appear to contain very little or nothing within it; whereas when the pressure of the Air is taken off in good part from the outsides of it, then those formerly latitant Particles disclose themselves by flying open into much bigger Zones, so as perhaps to be able to defend a [Page] thousand times bigger space from being entred into by their like or any other gross Particles, such as those of the Bladder. Now because the Pores of a Bladder are such as are not easily permeable by the Particles of Air, therefore these lurking Particles so expanding themselves must necessarily plump out the sides of the Bladder, and so keep them turgid until the pressure of the Air that at first coyled them be re-admitted to doe the same thing for them again.

Next, as for Rarefaction by heat, that will as naturally follow as the former from this Hypothesis. For the Atoms of fire flowing in in great numbers, and passing through with a very rapid motion, must needs accelerate the motion of these Particles, from which acceleration their Spring or endeavour outward will be augmented, that is, those Zones will have a strong nitency to flie wider open, (for we know that the swifter any body is moved circularly, the more do the parts of it endeavour to recede from the Centre of that motion) from whence if it has room will follow a Rarefaction. As for the conveyance of Light, that being according to Epicurus performed by the local motion of peculiar Atoms, their motions to and fro through this medium will be less impeded by the rarefi'd Air than by the condens'd; as indeed upon Experiment we shall really find them.

As for his third Objection drawn from his supposed attractive virtue of the thus-rarefi'd Air, that is quickly answered, by denying it to have any power at all of attraction; and by shewing (which is already done) that what effects he would have to be performed by the attraction of the included, is really done by the pressure of the ambient, Air.

And, lastly, the Phaenomena of my Lord Bacon's Experiment are sufficiently obvious and easie to be deduc'd.

So then, by granting Epicurus his Principles, that the Atoms or Particles of bodies have an innate motion; and granting our Supposition of the determinate motion and figure of the Aërial Particles, all the Phaenomena of Rarefaction and Condensation, of Light, Sound, Heat, &c. will naturally and necessarily follow: [Page] and the Author's Objections against this first way of Rarefaction will signifie very little.

As to the second way of Rarefactiore by the intrusion or intervention of some subtile matter or AEther into the spaces deserted by the rarefying Particles, which is that propos'd by the Assertors of a Plenum, this also is by the Author condemned, and branded with Impossibility. And why? First, because 'tis (he says) impossible that the above-mentioned Phaenomena of the Carp's Bladder can be explained by it. Secondly, because 'tis impossible to give a reason from it of the impetuous ascent of Water admitted into an exhausted Receiver. And, Thirdly, because 'tis impossible to explicate the Phaenomena of Gun-powder. His Reasons to confirm which three Impossibilities, because drawn from a mere mistake, or ignorance of those Hypotheses which have been invented by the Assertors of that Opinion, I shall pass over, and content my self to explain a way how these Impossibilities may become Possibilities, if not Probabilities.

And the way that I shall take, shall be that of the most acute Modern Philosopher Monsieur Des Cartes, published in his Philosophical Works: Which is this, That the Air is a Body consisting of long, slender, flexible Particles, agitated or whirl'd round by the rapid motion of the Globuli Caelestes, and the subtile Matter of his first Element, whereby they are each of them enabled to drive or force out of their Vortice all such other agitated Particles. Now the swifter these Bodies are whirl'd round, the more do their flexible parts flie asunder and stretch themselves out, and the more forcibly do they resist the ingress of any other so agitated particles into their Vortice, and consequently the slower their motion is, the less will be their resistance. And because there is a vast number of these whirled Particles lying one above another, and each Particle having its peculiar gravity; it will necessarily follow that the undermost (which to maintain their Vortice must resist so great a pressure) must very much be hindred from expanding themselves so far as otherwise they would, were there none of those [Page] incompassing agitated Particles that lay in their way: And that those being by any means removed, or they themselves by a more rapid motion of the Particles of their Vehicles, the first and second Element, (which is according to that Hypothesis an effect of Heat) more swiftly and strongly whirled round, they presently begin to expand themselves, and maintain a bigger Vortice than before. Now to perform what I just now promised, I shall endeavour to give a possible, if not a probable, cause of the objected Phaenomena. And, First, for that of the Carp's Bladder, where the Air is rarefi'd (says the Author) 1000 times, it will easily be explained by supposing the few Particles of the Air, which (whilst they sustain the pressure of all the incumbent Atmosphere) inconspicuously lurk within the Bladder, (each of them being able to maintain but a very small Vortice) to be by the subsiding Mercury in the Torricellian Experiment freed from the pressure of the Air, and their motion continuing the same (by reason that the Transcursion of their Vehicles is not at all or very little hindered either by the Glass or Bladder) their parts having room to expand themselves, will flie abroad to such Extensions as may perhaps make a Vortice 1000 times as big in bulk as what they were not able just before to exceed. Hence the Particles of the Air (being so gross as not easily to pervade the Pores of the Bladder) must necessarily drive out the sides of the Bladder to its utmost extent, and serve to fill the Receiver in the Magdeburgick Experiment. Now, whereas these Particles will by the same pressure of the Air be reduc'd to the same state they were in at first, that is, to be thronged into a very little room, and thereby be able to maintain a very small Vortice; the Air let in in the Torricellian Experiment reduces the Air in the Bladder to its former inconspicuousness, as the admission of the Water in the Magdeburg Experiment does that Receiver full of rarefi'd Air into the bigness of a Hazel Nut. Now the Water in this last-mention'd Experiment enters with a great impetuosity, because driven on with the whole pressure of the Atmosphere, and resisted only by the small force of the so-far. rarefi'd Air.

[Page]As for the Author's Objection against this way of Rarefaction drawn from the Phaenomena of Gun-powder, I shall endeavour to answer it by shewing them possibly explicable by a Cartesian Hypothesis. For supposing those Terrestrial parts of the Gun-powder to be first at rest, and afterwards agitated by the rapid motion of his first Element, there will be sufficient difference of the former and later condition in respect of Extension; and supposing the particular constitution of Gun-powder (arising partly from the Specifick forms of the Particles of its ingredients, Nitre, Sulphure and Char-coal, and partly from their proportionate commistion) to be such as will readily yield to the motion of his Materia subtilis, so soon as an ingress is admitted to it by the firing of any particular parcel of it, the Expansion will be speedy enough.

So then let us suppose a Barrel of Gun-powder placed in some close room, to some grains of which we will suppose some actual fire to be applied, by which actual fire (the Texture of the Powder being such) those grains are suddenly fired, that is, many Millions of parts, which before lay still and at rest, are by the action of the burning Coals shatter'd, as it were, and put into a posture ready to be agitated by the rapid motion of the Materia subtilis: into which posture they are no sooner put, than agitated and whirled sufficiently by it; whence follows a vast Expansion of that part of Gun-powder so fired. For each of its parts being thus whirl'd and hurried round, expel and beat off with great violence all the contiguous Particles, so as that each Particle takes up now 1000 times as much Elbow-room (if I may so speak) as just before serv'd its turn, and consequently those that are outermost take every one their way directly from the parcel or Corn they had lain quiet in, being hurried away by the sudden Expansion of the Particles that lay next within them; so that whatever grain or parcel of Gun-powder they chance to meet with, before they have lost their motion, they presently shiver and put into such a motion as makes them fit to receive the action of the Materia subtilis. Which subtile Matter being every where present, [Page] and nothing slow in performing its office, immediately agitates those also like the former; so that in a trice the Particles of the whole Barrel of Gun-powder are thus disordered, and by the motion the Materia subtilis must needs be hurried away with so great an impetuosity on all sides, as not only to break in pieces its slight wooden prison, and remove the lighter Particles of the ambient Air, but huge Beams, nay, vast accumulated Masses of the most compacted Structures of Stone, and even shake the very Earth it self, or whatever else stands in its way, whose Texture is so close as not to give its Particles free passage through its Pores. This understood, I see not, first, what the Author's three Arguments brought to prove his Objection signifie, for there are no more Corpuscles in the room before the Gun-powder is fired than after, nor is there any more matter or substance before the sides of the room by yielding give place for the external fluid Bodies to succeed, and the only change is this, that the Globuli secundi Elementi (as he calls them) are expell'd out of the room, and the Materia primi Elementi succeeds in the place of it. Nor do I see, secondly, what great reason he had for his grand Conclusion, Haeo abundè demonstrant, rarefactionem per hujusmodi corpuscula nullatenus posse explicari.

Having thus examined the Author's first Arguments, that Rarefaction cannot be made out by any other way than his; we shall find his other, which he brings to establish his own Hypothesis, much of the same kind. As, First, that his way of Rarefaction implies no Contradiction: For if the affirming a body to be really and totally in this place, and at the same time to be really and wholly in another, that is, to be in this place, and not to be in this place, be not a Contradiction, I know not what is. Next, that some learned School-men have thought so; to which I answer, more learned men have thought otherwise. And, lastly, that there are very plain Examples of the like nature to be found in other things; of which he only brings one, viz. that of the Rota Aristotelica, which upon [Page] examination we shall find to make as little to the purpose as any of the other.

An Explication of the Rota Aristotelica.

THe great Problem of the Rota Aristotelica, by his explication of which he pretends not only to solve all the difficulties concerning Local motion, quae Philosophorum ingenia bactenus valde exercuerunt, but to give an instance for the confirmation of his unintelligible Hypothesis of Rarefaction, wherein there is extensio seu correspondentia ejusdem rei ad locum nunc majorem, nunc minorem; we may upon examination find to be either a Paralogism, or else nothing but what those Philosophers said whom he accounts gravel'd with it. Of this Subject he begins in his 25th Chapter, where after he has set down a description of it, he makes an instance in a Cart-wheel; Rem ante oculos ponit rota alicujus currus, ejus (que) umbo seu lignum illudcrassum & rotundum cui infiguntur radii; siquidem dum progrediente curru ipsa rota circumduct a describit in subject a terra orbitam sibi aequalem, umbo ille describit in subjecto aëre orbitam (I suppose both here and before he means Lineam) se multo longiorem, utpote aequalem orbitae totius rotae, licet ipse non nist semel quo (que) fuerit circumvolutus. (Asfor what he says, that the Nave must be suppos'd to pass through the Air, and not to touch a solid Plain, I do not yet understand the force of his Reason, nor why he fets it down, making nothing to his present purpose, unless it were because he did not well understand the thing) In which, says he, the great difficulty is to explain how the Nave should be so turned about its Axis, ut partes suas successivè applicet lineae duplo plures partes habenti, id (que) motu perpetuo ac uniformi nè vel ad oculum instar interrupto. Which how true, and what great occasion he had to wonder at the solution of that Problem by the Example of a man standing still and another walking, we shall find by and by, when we come to explain the Problem: But first I shall examine his Hypothesis and Explication. [Page] And First, he supposes Time to consist of a determinate number of Indivisibles, (that is, such as have neither prius nor posterius included in them) which he calls Instants. And next he supposes the praesentiam localem seu ubicationem cujuslibet partis indivisibilis & virtualiter extensae esse quo (que) indivisibilem & virtualiter extensam: Which supposition so strangely exprest is no more than this, that the extension or space of his Indivisibles is also indivisible. But as for his Virtual Extension, I confess I understand as little what it is as I verily believe he did; and therefore I will proceed to his following supposition. His Third therefore is, That by how much more rare a body is, by so much the more are its Indivisibles virtually extended. Hence his Fourth is, That though these Indivisibles be really indisivible, yet they are virtually in quotvis partes divisibiles. Whence he deduces his Fifth Principle, That since these Indivisibles are really indivisible and virtually extended, they must necessarily be moved after the same manner that other indivisible and virtually-extended things are. His Instances are in the motions of an Angel and an indivisible piece of wood, which, he says, are both of the same kind. As for that of Angels, having no immediate Revelation, and a Spirit and its actions not falling under sense, and not having any third way by which to be inform'd, I shall leave him there to enjoy his fancies. But as for that of his piece of wood, we shall find it sufficiently full of absurdities and contradictions. And first, he calls it indivisible, but why I know not; for 'tis neither really nor yet mentally so: not mentally so by his fourth Principle, where he says that'tis virtualiter in quotvis partes divisibiles, by which word virtualiter he means the same thing with mentaliter, or nothing. Nor, secondly, is it really so: for then (according to the main business of his Book, as may be gathered from the first words of his Title Page. Tractatus de Corporum Inseparabilitate) it would be impossible that any thing in the world should be divisible; for he making an inseparable continuity, and that Bodies will rather be (I can't tell how) stretch'd beyond their own dimension in infinitum, than part from one another; [Page] a body may as soon pass through the dimensions of any one Indivisible, as pass between two. Next, he grants in the strange stretching or rarefaction of these Indivisibles a temporary motion of the condens'd Dimension; whence there will follow that there must be distinct places or Ubi's, it must be terminus à quo, terminus ad quem, & medium. And next, it were impossible to divide a line into two parts, supposing it consisted of an unequal number of Indivisibles; as if 101 Indivisibles of exceedingly-rarefi'd Air should be extended in length an Inch, it were impossible to divide that Inch into two equal parts. I might run over many more, but it would be too tedious to be here recited. As for his indivisible parts of Time, those also must necessarily be in quotvis partes divisibiles; for else the same body or Indivisible must necessarily be in divers places at the same instant. But because he can swallow, nay confidently affirm, this and many other such like contradictions and absurdities, I am not willing to mention them; and I think it would have made more for the Author's reputation if he had done so too. As for his last Chapter, where he applies these Principles to the Explication of the Rota Aristotelica, I have not here time to set down all the absurdities that any one that has but a smattering in the Mathematicks may observe: as, sometimes half an indivisible part of a Circumference may touch an indivisible of a Line; sometimes one may touch half, a quarter, a hundredth part, a whole one, two, ten, a hundred, &c. at the same instant; nay, an indivisible of a Circle may be all of it in a thousand places together, and the like. And this he brings as a great Argument to establish his Hypothesis of Rarefaction, pretending it to comprise many AEnigma's and very great difficulties; whereas the thing is very plain and easie, and contains no such obscurities. For if, for example, we suppose a Wheel ABCD to be moved in a direct motion from AIC to KLM, every point of it retaining the same position to that line that they had at the beginning of their motion, each of the points AEIGC will on a Plain, or in the Medium it pervades, pass through or describe a line equal to the line IL, and not only [Page] all the points lying in the line AIC, but all and every point of the whole Area of the Circle; this must necessarily happen if the Diameter AIC be moved parallel to it self: But if whilst it be thus moved with an equal progression, it be likewise moved with an equal circulation, the case will be altered. For then, first, each point will by this compound motion describe on the Plain or Medium either a perfect Cyclorid, as when the Wheel makes one perfect revolution, whilst the whole is progressively moved from I to L; or some Piece, as when the Wheel has not perfected its revolution; or more than a whole one, as when the Circle has made more than one whole revolution whilst it is moved in its determinate length. I shall here only consider the first, as pertaining more especially to my present purpose, and in regard the two later on occasion may be easily explicated by it. Next, each point of this Circle acquires from its compounded motion various degrees of Celerity as to its progression, according to its various position to a point which is always found in some part of the line drawn through the Centre of the circular motion perpendicular to the progressive. And it is found thus, as the Circumference to the Radius, so is the line of the progressive motion to the distance of the point from the Centre. And this happens because the line of Progression is equal to the Circle described on that distance as Radius; each point therefore of this smaller Circle, when it comes to touch the Perpendicular, must, as to its progressive motion, stand still: This point therefore will be the Centre of this compounded motion. Now because for the explication of the Rota Aristotelica we need not consider any other than those Points which are transient through or cross the Perpendicular line, we shall only examine them. Let then in our Example A be the Centre or immoveable point, the Circumference therefore ABCD will be equal to IL or AK by our Hypothesis. Now because the point I, which is the Centre of the Rotation, has only one motion, viz. that of Lation, its celerity will be equal to the single celerity of the Lation; we will therefore put it to have one degree, C, because it is moved with two motions, both tending the same [Page] way, and each equal to the velocity of I, must needs have two degrees of velocity. The point F, because moved with two motions, both tending the same way, the one (viz. its Lation) being equal to that of I, and the other (because it is but half as far distant from the Centre of Rotation as C, and therefore is moved but with half the celerity of C, which was equal to that of I) but half as quick, we will put to have one degree and an half. By the like method we might find the velocity of all the points in the Perpendicular, viz. such as we have there marked some of them; but it would be too tedious, we needing not to consider more than the two points A and E. The point at E being moved forward by its progression with the same velocity that I, but by its rotation (which is but half as swift as that of the Circle ABCD, that is double the Circle EFGH) being moved the contrary way or backwards with half the velocity, loseth half of its progression forwards. The point in A being by its progression moved forwards equally swift with I, and by its rotation (the Circle ABCD being equal to the line IL) being carried backwards with equal velocity, must necessarily stand still as to its progression. Now having shewn that the point A (being by reason of its two equal opposite motions at rest) does only touch a point of the line AK, and is not at all moved on it; and that the point E (being carried forward twice as fast by its progression as it is carried backward by its rotation, and thereby moved half as fast as the point I) does not only touch the line EK, but whilst it touches it is moved on it with a progressive motion half as swift as that of I: It will necessarily follow, that each point situate in E must necessarily describe a small line, which is a part of the whole EC. Now both the contact of the former, and the contact and progression of the later, being performed by an infinite succession of points in the space of an infinite succession of Instants; I see not any one difficulty of this Problem but may satisfactorily be given an account of by it, without having recourse to the Hypothesis of the determinate number of indivisibles of space and time, which at best will only come to this, that In such a determinate[Page]moment or minute space of time, (which consists of an infinite consecution of Instants, and has prius and posterius in it; though yet he will call it an Instant, and have it to have the same proprieties with an Instant used in the common Philosophical sense) such a determinate minute Corpuscle (which, though it have extension in length, breadth and thickness, yet will he not admit it to be divisible or have parts, no not though, according to his Hypothesis, the indivisible of one body may be rarefied to be as big in bulk as a million of the indivisibles of another, but will have it to be called and to be a real indivisible) will successively pass over such a determinate space or length (which yet he will not admit to be divisible, though according to his Principles it may equalize the length of millions of his other Indivisibles, nor admit a successive motion, but instantaneous, though that does necessarily put a body into two, three, ten, a hundred, &c. places at once; but will have these also to be indivisible.) Haste makes me pass over the absurdities about the contact of a Circle and a Line, and to comprise in short all that great Explication he has given of this and other intricate (as he calls them) Problems, which is this, That the reason of the celerity of the motion of some one of these indivisibles above another is, that it passes through a greater part of an Indivisible in the same instant than the slower; that is in plain sense no more than this, One body is swifter than another because it is moved faster. From whence he draws several Corollaries, as that Hence may be given a reason why an Eagle is swifter than a Tortoise, viz. because it moves saster. I should have solved several Objections which may be brought against the divisibility of Quantity in infinitum; but that as all the Scholastick Writers are full of them, so it is a Subject which we are least able to dispute of having very little information of the nature of Infinity from the Senses.

FINIS.

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The Citations Englished.

CHap. 2. Pag. 3. Cum tota vis, &c. Being the whole power of the Spring of the Air depends upon the AEquilibrium of its weight with twenty nine Inches and an half of Quicksilver, so that this Spring doth neither more nor less in a shut place, than is done by that AEquilibrium in an open place: It is manifest, seeing we have shewed the AEquilibrium to be plainly fictitious and imaginary, that the Spring ascribed to the Air is so likewise.

P. 4. Nam si Tubus, &c. For if a Tube but twenty Inches long (such as we used in our first Argument) be not quite filled with Quicksilver, as before, but a little space be left betwixt the Mercury and the Finger on the top of the Tube, in which Air only may abide: We shall find that the Finger below being removed, the Finger on the top will not only be drawn downwards, as before, but the Quicksilver shall descend also, and that notably, viz. as much as so small a parcel of Air can be extended by such a descending weight. So that if instead of Air, Water or any other Liquor which is not so easily extended be put in its place, there will be no descent at all.

Hence, I say, against this Opinion an Argument is framed: For if the external Air cannot keep up those twenty Inches of Quicksilver from descending, as we have proved; how shall it keep up twenty nine Inches and an half? Assuredly these can no way be reconciled.

Ibid. Dices fortè, &c. You will perchance say, that the Quicksilver therefore doth in the alledged case descend, because it is thrust down by that parcel of Air which dilates its self by its own Spring.

Ibid. Sic deberet, &c. So should the Finger be rather thrust from the top of the Tube, than thereby fastned to it; because this Dilatation must be made as well upwards as downwards.

P. 6. Concipi, &c. It cannot be conceived how that Air should dilate it self, or thrust down the Mercury, unless by taking up a greater place; which thing these Authors are much against, asserting that Rarefaction can be made no otherways than by Corpuscles or Vacuities.

Chap. 3. p. 7. Si, &c. If you take a Tube open at both ends of a good length, suppose forty Inches long, and fill it with Mercury, and place your Finger on the top as before, taking away your lower Finger you will find the Mercury to descend even to its wonted station, and your Finger on the top to be strongly drawn within the Tube, and to stick close unto it. Whence again it is evidently concluded that the Mercury placed [Page] in its own station is not there upheld by the external Air, but suspended by a certain internal Cord, whose upper end being fastned to the Finger draws and fastens it after this manner into the Tube.

Chap. 4. p. 8. Sumatur, &c. Take a Tube shorter than twenty nine Inches and an half, for instance of twenty Digits, not shut, as hitherto, at one end, but with both ends open: let this Tube, its Orifice being immers'd in restagnant Mercury, and one Finger being plac'd underneath, that the Mercury to be poured in run not through, be filled with Mercury; and then another Finger be applied to its Orifice, to close it well: Which being done, if you draw away your lower Finger, the upper will be found to be strongly drawn and suck'd into the Tube, and so stifly to adhere to it, (or rather to the Quicksilver, as I shall hereafter shew) that it will elevate the Tube it self with all the Quicksilver, and make it continue to hang pendulous in the Vessel.

From which Experiment this Opinion is most clearly refuted: For, seeing according to it the Quicksilver in such a Tube but twenty Inches long must be thrust upwards by the preponderating Air; it will never by it be explained how this Finger is so drawn downwards, and made so strongly to stick to the Tube. For it cannot by the Air thrusting upwards be thus drawn downwards.

p. 10, 11. Quod vel, &c. Which is thence confirmed, Because if that preponderating Air succeeds, as is asserted, in the place of the lower Finger which was withdrawn, that is, if it uphold the Quicksilver after the same manner which it was upheld by the lower Finger applied under it; it is manifest, according to this Opinion, that the Finger on the top ought not to be more drawn downwards after the lower Finger is removed than before. Seeing then that Experience teacheth the contrary, it is manifest that Opinion must be false.

Chap. 5. p. 11, 12. Quarto, &c. In the fourth place it is impugn'd, Because thence it would follow that Quicksilver through a like Tube might be suck'd with the same easiness out of a Vessel that Water is suck'd out of the same. Which notwithstanding is contrary to Experience, by which we are taught that Water is easily drawn into the mouth of him that sucks, whereas Quicksilver cannot be drawn thither by his utmost endeavour, nay, scarce unto the middle of the Tube.

The sequel I thus manifest: Because seeing, according to this Opinion, that the Liquor underneath, whether it be Water or Mercury, may so ascend, no more is requir'd but that the Air shut in the Tube may be drawn upwards by sucking; which being drawn up, the Liquor underneath will immediately ascend, being thrust thither by the external Air now preponderating, (as Pecquet declares in his Anatomical Discourse, p. 63.) It is [Page] manifest that the Mercury may be suck'd out with the same easiness that Water is suck'd out with. Which being so evidently against Experience, the Opinion from whence it is deduced must needs be false.

p. 13. Ne (que) hoc, &c. And not only this, but over and above, if a Glass Diabetes or Syringe be made of a sufficient length, and after that the Sucker is thrust into the utmost Orifice, it be placed according to use in the Mercury underneath; he finds that as soon as the Sucker is drawn out, the Mercury follows, and ascends to the same height of two Feet and three Inches and an half. And when afterwards, although no greater force be added, the Sucker is drawn higher, he finds that the Mercury stands, and follows no further, and so that space is made empty which remains between the Mercury and the Sucker.

p. 15. Maneat igitur, &c. Be it therefore confirm'd by so many Arguments, of which every one is sufficient in it self, that Quicksilver (the Experiment being made in an open place) is not upheld from falling by the weight of the external Air.

Cap. 6. Ibid. Argentum, &c. That Quicksilver in a close place is not upheld from falling by the Elater or Spring of the Air.

Ibid. Cum tota, &c. Seeing the whole power of this Spring depends upon the already-confuted AEquilibrium of the Air with 29 Inches and an half of Quicksilver, so that this Spring does neither more nor less in a close place than is done by that AEquilibrium in an open place; it is manifest, seeing this AEquilibrium is already shewn to be plainly fictitious and imaginary, that the Spring of the Air is so likewise.

p. 16. Nec plus, &c. And that this Spring doth neither more nor less in a close place, than is done by that AEquilibrium in an open place.

Ibid. Adde, &c. Add, that seeing the Experiments brought in the Chapter above of the adhesion of the Finger, &c. are alike in a close and an open place: it is necessary and certain that the same Arguments made against the AEquilibrium have force against the Spring of the Air.

p. 17. Et profecto, &c. And really if these Authors would consider how great a difficulty there is in explaining this Spring of the Air, unless the same Air by it self alone may take up a greater place, I believe they would readily alter their Opinion.

Part 2. Chap. 1. p. 19. Constet hoc, &c. This appears from what has been already spoken in the preceding Chapter: For the Quicksilver descending cannot so draw the Finger downwards, and fasten it unto the Tube, unless it be hung upon the Finger by such a Cord, which by its weight it vehemently stretches, as is manifest by it self.

Ibid. Respondeo, &c. I answer, That this comes to pass that there may be no Vaculty, seeing there is nothing else there that can succeed into the place of the descending Quicksilver.

[Page]Ibid. And hence is confirm'd that common Axiom used in the Schools for so many Ages past, that Nature doth abhor a Vacuum.

Ibid. Nam licet, &c. For though the immediate cause why Water (for instance) doth not descend from a Gardener's Watering-pot (for that Example they use) stopt on the top, is not the fear of a Vacuum, but the reason now mentioned, namely, That there is not weight sufficient to loose that conjuncture by which the Water doth adhere to the top of the closed Water-pot: Nevertheless in the end we must of necessity come to that Cause.

p. 20. Quae quidem, &c. Which traction and adhesion when it cannot proceed but from some real Body placed between the Finger and the Mercury, it is manifest that that space is not empty, but filled with some true substance.

Ibid. Eo quod, &e. Because no visual species's could proceed either from it, or through it, unto the eye.

Ibid. Vera, &c. To be filled with any true substance.

p. 24. Huc etiam, &c. And to this purpose make those considerable Vibrations with which Quicksilver is stirred in its descent: For the same thing happens here that befalls other Pendula in their fall from on high.

p. 27. Argenium dum, &c. Quicksilver while it fills the whole Tube doth not only touch its top, (as you would think at the first sight) but doth firmly stick unto it also; as it is manifest from the Experiment mentioned in the first Argument of the third Chapter, concerning the Tube open at both ends.

Ibid. Licet illud, &c. Though that Orifice of the Tube be anointed with Oyl, or any other matter that will hinder adhesion, nevertheless the Finger will no less firmly stick than before.

p. 28. Partes, &c. That the parts of Air it self so shut up in the Tube (which otherwise are so easily severed) are now so firmly glued to one another, that they make (as we see) a strong Chain, by which not only Water but even weighty Quicksilver is drawn on high.

Ibid. Rarefactionem, &c. That the Rarefaction or Extension of a Body so as to make it take up more space is not only made by Heat, but by distension or a certain disjoyning power; as on the contrary Condensation is not only made by Cold, but also by Compression, as infinite Examples bear us witness.

p. 29. Cum per, &c. Seeing by the first Note 'tis manifest that the Quicksilver doth so stick to the top of the Tube, and by the second Note the Rarefaction is made only by the mere distension of the body; it so comes to pass that the descending Quicksilver leaves its external or upper superficies fixed unto the top of the Tube, and by its weight doth so stretch [Page] and extenuate it, untill it becomes easier to leave another superficies in like manner, than to extend that any further. It leaves therefore a second, and doth by its descent extend that a little further, until it becomes easier to separate a third than to extend that any further: And so forwards, until at length it hath no power to separate or extend any more superficies, namely, until it comes unto the height of 29 Inches and an half; where it acquiesces, as we have declared in the first Chapter.

p. 30. These Surfaces seem to be separated from the Quicksilver, and to be extended into a most slender string by the weight that falls down, after the same manner that in a lighted Candle surfaces of like sort are separated from the Wax or Tallow underneath by the heat above, and are extenuated into a most subtile flame. In which it is worth observation, that as that flame doth doubtless take up more than a thousand times a greater space than the part of the Wax of which the flame was made took up: So is it here to be thought, that that string doth take up a space more than a thousand times as big as that which the small particle of Mercury, from whence it arose, did before take up. As also it doubtless happens when such a particle by a fire underneath is turned into a vapour.

p. 36. Corpore, &c. A body taking up a place, for instance, twice as big as it self; it is of necessity that every part of it must likewise take up a place twice as big as it self.

p. 41. Juxta, &c. According to the more probable Opinion such a virtual extension of a corporeal Being is not to be granted, as being only proper to such as are Spiritual.

Ibid. Praestat, &c. It is better to continue in the common Opinion, which hath been hitherto received in the Schools: which although it doth not clearly resolve all difficulties, yet it doth not openly lie under them.

Ibid. Necessario, &c. We must needs confess that one and the same part must be in two places adequately. For seeing it is indivisible, and takes up a greater place than before, it must of necessity be all in every point of that place, or that be virtually extended through all that space.

p. 43. Cumtempus, &c. Seeing Time is a Being esfentially successive, so that neither by divine power can two of its parts exist together.

p. 44. Respondeo, &c. I answer, that all these things happen because the Gun powder so kindled and turned into flame takes up a much greater space than before. Whence it comes to pass that seeing the Chamber was before quite full, by this means the walls are broken that there may be no penetration of bodies.

p. 48. Partim, &c. Sometimes within the Chapel, sometimes in the open Air; the wind sometimes blowing, and sometimes being still.

[Page]p. 52. Sed dici, &c. But it may be said, that on the top of the Mountain it therefore descended after that manner, because the Air was more cold there, or of some other temperature, such as might cause this descent.

p. 68. Hoc esse, &c. That this is the difference between Pression and Suction, that Suction makes such an adhesion, and Pression doth not.

p. 69. Hoc quo (que) &c. And even this Experiment doth very well agree with our Principles: For seeing by this depression of the Sucker, the Air shut up in the cavity of the Cylinder is separated from the Cylinder, and doth descend together with the Sucket, (as we have, Chap. 13. observed of Water descending together with Quicksilver) it comes to pass that in that whole depression new surfaces are taken from that descending Air, and stretched out, as we have there explained it in the case of descending water. Since therefore such surfaces are as easily slipt of and extended in the end of the depression as in the beginning; it is no wonder that there is found the same difficulty of depressing it at both times.

Ibid. Eo magis, &c. That the Air is so much the more extended and rarefied, by how much the more is thence exhausted, and so doth acquire a greater force of contracting it self.

p. 71. At profecto, &c. But truly it seems not credible that this most soft Air should so vehemently compress a Glass on all sides (especially one of that thickness there mention'd) as to break it.

p. 72. Verius, &c. It is therefore more truly answered, that the Glass is therefore so broken, because by that exsuction its sides are more vehemently drawn inwards than (by reason of the figure unfit for resistency) they were able to resist. For seeing the included Air doth most firmly stick to the sides of the Glass, to draw out the Air will be nothing elst but to endeavour to bend the fides of the Glass inwards.

Ibid. Sed profecto, &c. But truly this seems too far remov'd from Truth, and may be by this alone sufficiently refuted. Because if the pressure of the Air which descends by that Tube into the Vial be so great as to break the Vial it self, it ought certainly, before the breaking of the Vial, very much to move the water in which the Tube is immers'd, and to excite bubbles in it, &c. as appears, if any one blowing through that Tube doth make but an ordinary pressure upon the water. But it is sure that the water before the Vial is broken doth not move at all: as the Experimenter will find.

p. 73. Licet, &c. Though the Tube had been shut at the top, the Vial had doubtless been broken after the same manner.

p. 74. Sed rectius, &c. But it is more rightly thence inferr'd that that Cylinder did nothing there before.

p. 75. Dice, &c. I say then that the Quicksilver doth by that exhaustion [Page] so descend in the Tube, because it is drawn downwards by the Air incumbent upon the restagnant Quicksilver. For that incumbent Air, being by its exhaustion greatly rarefied and extended, vehemently contracts its self, and by this contraction doth endeavour to lift the restagnant Mercury out of its Vessel; whence it comes to pass that (the restagnant Mercury now less gravitating upon the bottom of its Vessel) the Quicksilver in the Tube must descend, as is manifest in it self: So that it is no wonder that, the external Air afterwards entring, the Quicksilver again ascends, seeing by that ingress the force which elevates the restagnant Quicksilver is weakned.

Ibid. At (que) hinc, &c. And hence is a reason also given of another thing which is there noted, namely, that by the violent intrusion of the external Air into the Receiver the Quicksilver ascended considerably above 29 Inches and an half. For as by the extraction of the Air the Quicksilver is deprest below its station, so by the intrusion of new Air it is elevated above it.

p. 77. Nam si, &c. For if it were kept up by that, it ought rather to ascend than descend in colder weather, because the Air then would be more dense and heavy. Therefore the Quicksilver is not upheld by the AEquilibrium of Air, as is asserted.

p. 78. Hinc fit, &c. Hence it comes to pass, that this Funicle being contracted by the cold, the water doth ascend in cold weather; but doth descend in hot, because by heat the Funicle is dilated.

Ibid. Ego certè, &c. I truly do not doubt but there are some such occult causes, by which the slender Funicle that suspends (as we mentioned in the 10. Chapter) the Quicksilver in the Tube is sometimes lengthned, sometimes shortned, and so doth sometimes let down, and sometimes lift up the Quicksilver.

p. 79. In decimo nono, &c. In the 19. he shews that water doth in the same manner descend upon the exhausting the Receiver, as he had shewn Quicksilver in the foregoing Chapter to descend. Of both which seeing there is the same cause, there is no reason we should any longer insist on this.

p. 80. Nam fi, &c. For if it were done so, these bubbles ought not so to have ascended from the bottom of the Vessel, (as it is asserted they did, both in this and the following Experiments that treat of bubbles) but from the upper part of the water, where they are less comprest; as it is apparently manifest.

p. 81. Respondeo, &c. I answer that the water, upon that exhaustion of the Air, doth not so ascend of its own accord, but is violently drawn or lifted upwards by that rarefied Air contracting it self. For as water doth [Page] suffer some compression (as appears by experience) so here also it suffers some distension. And hence it is clearly manifest why these bubbles should arise rather from the bottom of the Vessel, than from the upper part of the water. For when that vehement suction doth endeavour to elevate the water from the bottom of the Vial, there arises there a certain subtile matter, which being turned into bubbles doth so ascend as is mentioned in the 15. Chapter and the 4. Experiment.

p. 82. Certum esse, &c. It is certain that that Opinion is sufficiently refuted by this single Experiment.

p. 83. Necesse, &c. It must needs be that that stone could not otherwise descend, than by leaving behind it such a thin substance as is left by Quicksilver or Water descending in like manner.

Ibid. Vnde, &c. Whence I plainly conceive that if two perfectlypolish'd Marbles were so joyned that no Air at all were left between them, they could not be drawn asunder by all the power of Man.

Ibid. Vti etiam, &c. Which also is confirmed by the Example the Author there brings of a Brass Plate sticking so close to a Marble Table, that by a lusty Youth, who boasted of his own strength, it could not be lifted off by a Ring fixed to its Centre.

p. 84. Eodem, &c. Almost the same manner as we see in Cupping-glasses applied to a Patients back, in which the flame being extinct, the rarefied Air contracting it self doth so vehemently (as we see) lift up, and draw the flesh within the Glass.

p. 85. In his, &c. In these three there is nothing occurs to be peculiarly here explicated, the account of which is not easie from what is already delivered.

Ibid. Existimo, &c. But I think that Whiteness should be rather called a reflex than an innate light, because, as the Author bears witness, it appears not in the dark, but only in the day, or by Candle-light.

p. 86. Verum, &c. But it seems impossible that such Animals should dye so soon only for want of a thicker Air.

p. 87. Quia per, &c. Because by the self-contraction of the rarefied Air their breath is drawn out of their bodies.

Ibid. At (que) hinc, &c. And thence also arose those vehement Convulsions, which the Author there mentions certain small Birds to have endured before their death.

p. 89. In mala, &c. In a bad Cause they can do no other; but who compell'd them to undertake a bad Cause?

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A Summary of the Contents of the several Chapters.

PART I.

WHerein the Adversaries Objections against the Elaterists are examined.

CHAP. I.

The occasion of this Writing, pag. 1. Franciscus Linus his civility in writing obliges the Author to the like, p. 2. Books concerning the Torricellian Experiment wherewith the Author was formerly unacquainted, ibid. The Inconvenience of Linus's Principles, ibid. The division of the ensuing Treatise into three parts.

CHAP. II.

A repetition of the Adversary's Opinion and Arguments. His Arguments against the Weight of the Air examined, p. 4. An Experiment of his to prove that the external Air cannot keep up twenty Inches of Quick-silver from descending in a Tube twenty Inches long, ibid. The Author's answer and reconciliation of the Experiment to his Hypothesis, p. 5. and the relation of an Experiment of the Author's, wherein only water being employed instead of Quick silver, without other alteration of the Adversaries Experiment, it agrees well with and confirms the Author's Hypothesis, and his Explication of the mentioned Experiments, ibid. That Water hath no Spring at all, or a very weak one, p. 6. The second Argument examined, ib. Whether the same quantity of Air can adequately fill a greater space, p. 7. The conceivableness of both Hypotheses compared, ibid.

CHAP. III.

Another Argument of the Adversaries, from an Experiment wherein the Mercury sinking draws the Finger into the Tube, examined. Q. Whether the Mercury placed in its own station is upheld by the external Air, or suspended there by an internal Cord? p. 7, 8.

CHAP. IV.

A repetition of Franciscus Linus his principal Experiment, wherein in a Tube of twenty Inches long the Finger on the top is supposed to be strongly drawn and suck'd into the Tube, p. 8. The Experiment explicated without the assistance of Suction, by the pressure of the external Air upon the outside of the Finger, thrust, not suck'd in, p. 9. Franciscus Linus his argumentation considered, p. 10.

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CHAP. V.

The Eximiners last Experiment considered, in which he argues against the Author's Hypothesis, because Mercury is not suck'd out of a Vessel through a Tube so easily as Water is, p. 11, 12. An Experiment of Monsieur Paschall shewing, that if the upper part of a Tube could be freed from the pressure of all internal Air, the Mercury would by the pressure of the outward Air be carried up into the Tube as well as Water, till it had attained a height great enough to make its weight equal to that of the Atmosphere, p. 13. Why in a more forcible respiration the Mercurial Cylinder is raised higher than in a more languid, p. 14. A Remark by the bie, That the contraction of the Adversaries supposed Funiculus is not felt upon the Lungs, p. 15.

CHAP. VI.

The examination of the Adversaries 4th Chapter, p. 15. That the Spring of the Air may have some advantage in point of force above the Weight of it, p. 16. That it is unintelligible how the same Air can adequately fill more space at one time than at another, p. 17.

PART II.

Wherein the Adversaries Funicular Hypothesis is examined.

CHAP. I.

Wherein what is alledged to prove the Funiculus is considered; and some Difficulties are proposed against the Hypothesis.

The nature of this supposed Funiculus described, p. 18. That according to the Adversaries Opinion this Funiculus is produced by Nature only to binder a Vacuum, p. 19, 20. The Adversaries proofs that there is no Vacuum examined, p. 20, 21. That where no sensible part is un-enlightned, the place may not be full of light, p. 21. The same true in Odours, ibid. That there may be matter enough to transmit the impulse of Light, though betwixt the Particles of that matter there should be store of Vacuities intercepted, p. 22. That a solid Body bath no considerable sense of pressure from fluid bodies, p. 24. Of the causes of the Vibrations of Quick-silver in its descent, p. 24, 25.

CHAP. II.

Wherein divers other Difficulties are objected against the Funicular Hypothesis. As that in Liquors of divers weights and natures, as Water, Wine and Quick-silver, there should be just the same weight or strength to extend them into a Funiculus, p. 27. That whereas the Weight and Spring of the Air is inferr'd from unquestioned Experiments, the account of that Hypothesis is strange and unsatisfactory. As that the Quick-silver doth not only touch the top of the Glass, but stick to it; That Nature wreaths a little rarefied [Page] Air into a strong rope even able to draw up Quick-silver, p. 27, 28. That Rarefaction is performed by a certain unknown force, or vis divulsiva, ibid. That thin Surfaces are left successively one after another, that these Surfaces are contrived into strings, that may be stretch'd without being made more slender, &c. p. 29. The illustration of the manner how his Funiculus is made, from the rarefaction of Wax or Tallow in a lighted Candle, is considered, p. 30. and shewed not to be apposite, ibid. Divers other difficulties and improbabilities manifested in the Funicular Hypothesis, p. 31. Of the inward Spring necessary to the contraction of his Funiculus, p. 31, 32. An Argument from a Pendulum's moving freely in an exhausted Receiver, that the medium it moves in doth not consist of innumerable exceedingly-stretch'd strings, p. 35.

CHAP. III.

The Aristotelean Rarefaction proposed by the Adversary examined. What Rarefaction and Condensation is, p. 34. Three ways of explicating how Rarefaction is made, p. 34, 35. Absurdities in resolving the Magdeburg Experiment by the Aristotelean way of Rarefaction, p. 36. The inconveniences of the several Hypotheses compared, p. 37. The difficulties in the Adversaries explaining Rarefaction by Bodies infinitely divisible, ibid. The difficulties of explaining it by supposing Bodies made up of parts indivisible, p. 39, 40. The difficulties wherewith his Condensation is incumbred, as that it infers Penetration of Dimensions, &c. p. 41.

CHAP. IV.

A Consideration pertinent to the present Controversie, of what happens in trying the Torricellian and other Experiments at the top and feet of Hills. That the Funicular Hypothesis is but an Inversion of the Elastical, one supposing a Spring inwards, the other outwards; one performing its effects by Pulsion, the other by Traction, p. 46. That these trials on the tops and feet of Hills determine the case for the Author's Hypothesis, p. 47. The truth of the Observation of Monsieur Paschall confirmed, p. 48. and the several trials that have been made of it related, ibid. A trial of the Author's from the Leads of the Abbey-Church at Westminster, p. 50, 51, 52. That the subsidence of the Mercury at the top of a Hill proceeds from the lightness of the Atmospherical Cylinder there, p. 53. The relation of an Experiment lately made at Hallifax Hill in confirmation of the former, p. 54.

CHAP. V.

Two new Experiments touching the measure of the force of the Spring of the Air compress'd and dilated. That it is capable of doing far more than the necessity of the Author's Hypothesis requires, p. 55. The first Experiment, of compressing Air by pouring Mercury into a crooked Tube, related, ibid. Wherein the same Air being brought to a degree of density twice as [Page] great, obtains a Spring twice as strong as before, p. 57. A Table of the Condensation of the Air according to this Experiment, p. 58. Particular Circumstances observed in the making the Experiment, ibid. How far the Spring of the Air may be increased, p. 60. Of the decrement of the force of dilated Air, p. 61. A Table of the Rarefaction of the Air, p. 62. Particular Circumstances in making the Experiment whence this Table was drawn, p. 63, &c. That the free Air here below appears to be near as strongly comprest by the weight of the incumbent Air as it would be by the weight of a Mercurial Cylinder of 28 or 30 Inches, p. 65.

PART III.

Wherein what is objected against Mr. Boyle's Explications of particular Experiments is answered.

The entrance into this Part of the Discourse, with an advertisement how far only it will be requisite to examine the Adversaries assertions and explications, the Hypothesis on both sides being before considered, p. 67.

A defence of the first and second Experiments, concerning the intrusion of the Finger into the Orifice of the Valve of the evacuated Receiver, p. 68.

A defence of the third Experiment, why the Sucker being drawn down there is no greater difficulty in the end than in the beginning of the depression, ibid.

Of the fourth Experiment, touching the swelling of a Bladder upon the exhaustion of the ambient Air, and proportionably to that exhaustion, p. 70, 71. The Author's and the Funicular Hypothesis in the explication of this Phaenomenon compared, ibid.

Of the fifth Experiment, ibid.

Of the eighth Experiment, about the breaking of a Glass-Receiver which was not globular upon the exhaustion of the inward Air, p. 71. Whether it were more likely to be broken by the pressure of the Atmosphere without, or a contraction of a string of Air witbin, p. 72.

Of the ninth Experiment, ibid. Whether the breaking of the Vial outwards in the exhausted Receiver, was caused by the pressure of the Atmosphere through the Tube which was open to the ambient Air, p. 73.

Of the 17. Experiment, p. 74, 75, 76. The Torricellian Experiment being made within the Receiver, whether the descent and ascent of the Mercury in the Tube, under and above its wonted station, be caused by the debilitated and strengthned Spring of the Air, ibid.

Of the 18. Experiment, p. 77, 78. Whether the Authors or the Funicular Hypothesis assign the more probable cause why a Cylinder of Mercury did in Winter rise and fall in the Tube, sometimes as Water in a weather-glass [Page] according to the laws of Heat and Cold, and sometimes contrary thereunto, ibid.

Of the 19. Experiment, p. 79.

Of the 20. Experiment, p. 79, 80. Some mistakes in the Adversary of the Author's meaning about the Spring of the Water, and the places whence the bubbles arose, ibid. The Hypotheses compared, ibid.

Of the 31. Experiment, p. 81, 82, 83. Of the cause why the Marbles fell not asunder in the exhausted Receiver, though a weight of four Ounces were hung at the lower stone, ibid. Whether the account of the Author or Adversary be more satisfactory, ibid.

Of the 32. and 33. Experiments, of the re-ascent of the Sucker and its carrying up a great weight with it upon the exhaustion of the Receiver, p. 84. How the flesh and neighbouring blood of a Patient is thrust up into a Cupping-glass, ibid.

Of the 37. Experiment, and the cause of the appearance of light or whiteness therein, p. 85.

Of the 40. and 41. Experiments, concerning the cause of the sudden death of Animals in the exhausted Receiver, p. 85, 86.

Of the 42. and 43. Experiments, p. 87.

The Conclusion, p. 91, 92.

FINIS.

§

§

§

[Page]

[Page]

AN EXAMEN OF Mr. T. HOBBS his Dialogus Physicus De Naturâ Aëris.

As far as it concerns Mr. BOYLE's Book of New Experiments touching the Spring of the Air, &c.

With an APPENDIX touching Mr. Hobbs's Doctrine of Fluidity and Firmness.

By the Author of those Experiments.

LONDON, Printed by M. Flesher, for Richard Davis Bookseller in Oxford, 1682.

[Page]

[Page]

THE PREFACE.

HAVING, soon after I had begun the following Examen of Mr. Hobbs's Dialogue, been diverted for a good while by divers urgent Avocations from pursuing it; I was in the mean time informed by learned men (some of whom keep great Correspondences with the Virtuosi abroad) that my publishing any thing against his Objections would not be necessary, nor was much expected: Whereupon I should perhaps have declined resuming an Employment, that to a person of my humour could not be delightfull; but that besides those Inducements mentioned at the beginning of the following Treatise, it came into my mind that my Adversary, not content to fall upon the Explications of my Experiments, has (by an Attempt, for ought I know, unexampled) endeavoured to disparage unobvious Experiments themselves, and to discourage others from making them. Which if he could by his Dialogue effect, I dare be bold to say, he would far more prejudice Philosophy by this one Tract, than He (and that it may not seem said to undervalue him, I shall adde, or any Man else) can promote it by all his other Writings. Wherefore, though his disparaging of Experiments would probably have much more Authority (especially with considering men) if he had been the Author of considerable ones, or did appear to be more than ordinarily skilled in them: yet lest for all this his Fame and Confident way of writing might prejudice Experimental Philosophy in the minds of those who are yet strangers to [Page] it, I thought it not amiss, both to go on with the Discourse I had begun, and to enlarge it beyond what I first designed; and accordingly, to the intended Vindication of the main points of our Doctrine, The Weight and Spring of the Air, which (if I mistake not) we have firmly established, we have added an Examen, that otherwise we should scarce have made, of the greatest part of the Physiological passages in Mr. Hobbs's book, most of which I thought might be rationally question'd, and many of them clearly disprov'd. And in pursuance of this, though I did not perhaps alwayes think my self oblig'd to prosecute things further than the nature of my Design requir'd, or to forget that the Matters in dispute were not all of an equal weight; yet the Reflexions I have employ'd will, I presume, be found sufficient to shew both that 'tis easie even for a great Wit frequently enough to mistake, and much more frequently to miss of clearly demonstrating what he pretends in matters Physical, for want of having sufficiently considered the Experiments he would be thought to despise; and that Mr. Hobbs's Adversaries need not be much ashamed of the Name he is pleased to give them of Experimentarian Philosophers. It was also suggested to me, that the dangerous Opinions about some important, if not fundamental, Articles of Religion I had met within his Leviathan, and some other of his Writings, having made but too great Impressions upon divers persons, (who, though said to be for the most part either of greater Quality, or of greater Wit than Learning, do yet divers of them deserve better Principles) these Errors being chiefly recommended by the Opinion they had of Mr. Hobbs's demonstrative way of Philosophy; it might possibly prove some service to higher Truths than those in Controversie between him and me, to shew that in the Physicks themselves his Opinions, and even his Ratiocinations, have no such great advantage over those of some Orthodox Christian Naturalists. But for all this, as little as I would grudge to write a much longer than the following Discourse to do Religion the least [Page] service; yet thinking it fit to leave Controversies of this kind to those whom they more particularly concern, I should scarce in the Introduction to a Dispute about the Air have at all mentioned any thing of this nature, but that Mr. Hobbs in the Preface to his Dialogue is pleased (though I know not to what purpose in that place) to speak without limitation or distinction (and consequently unwarily enough at least) of the things said in the Books of Naturalists concerning immaterial substances, (and sure some things true, (at least That there are such Beings) as well as some things erroneous, are there said:) though he hath been by the learned Dr. More and others publickly accused to have taught, That 'tis absurd to believe that there either are or can be any. Which yet methinks he should not do, since elsewhere —Ne (que) hominis Philosophi esse censeo corporum quorundam, ut solis & stellarum, mirabiles supponere magnitudines, contra vero mirabiles exiguitates non admittere, cum Virtutis ejusdem infinitae sit utra (que) creare tam maxima quam minima. Mr. Hobbs in his Dialogue of the Air, page 11. See also page 5. and elsewhere. and in this very Dialogue he builds several things in his Philosophy upon the Creation of the World, and an Infinite Power: And how a thing material can create matter and have an Infinite Power, I confess I do not understand.

I doubt not but Critical Readers will think I might have excepted against many more particulars in Mr. Hobbs's Book than I have Examin'd; and indeed about this I dare not contend with them. For besides that I may through haste and indisposedness to quarrel, have over-seen several things which an Eye either severer or more attentive would have observ'd; I purposely past by divers things I did not altogether over-look; partly, because I thought it needless to question them (having no want of other Objections) and partly, because I could not do so in few words, and was loth to engage in needless and long-winded Disputes: And perhaps I was too weary of my Employment to be willing to spend many words when I could safely spare them. [Page] And though others will possibly think it strange, that a Member of the Society he is so severe to should not take notice of such passages as these, Nam conveniant (sayes he, speaking of the Virtuosi that meet at Gresham College) Studia conferant, Experimenta faciant quantum volunt, nisi & principiis utantur meis, nihil proficient; and again, Nae illi quae dicerent non videntur cogitasse, sed sortitos esse; and elsewhere, Conjicere hinc licet, quam sint boni ratiocinatores, & quae sit ab illis expect and a Philosophia Naturalis; and (to trouble you no more) Ad causas autem propter quas proficere ne paululum quidem potuistis nec poteritis, accedunt etiam alia, ut odium Hobbii, quia nimium liberè scripserat de Academiis veritatem: Nam ex eo tempore irati Physici & Mathematici veritatem ab eo venientem non recepturos se palam professi sunt: Though, as I said, some may wonder I should silently pretermit such passages as these; yet besides what I elsewhere say by way of Account of my so doing, I shall here tell them, that I presume some sorts of Readers will more easily pardon me for neglecting such Expressions, than they will Mr. Hobbs for using them. And I confess, I thought I should find it more easie to say nothing at all to such passages, than say any thing without saying somewhat that would offend a Person that could allow himself to say such things. Though I ignore not that divers Readers will much the less rellish the following Discourse, for my having, perchance not altogether for want of knowing how to write otherwise, forborn to furnish it with quick and smart Expressions, which are wont to be employ'd in Disputes, to expose or depreciate an Adversaries Person or Cause, and which are usually not the least things that serve to amuse such Readers, and engage their attention. But I fear I have much less need to make Excuses for my Omissions, than for having in the following Examen been reduc'd by the Nature of my Task, to say so many things which Intelligent Readers need not be taught by me. And therefore such shall have my consent to skip, if they please, the whole [Page] Discourse; which though I could scarce upon such an Occasion make a very Instructive one, yet if they will be pleas'd to forgive me its Barrenness, I hope hereafter to avoid the like Temptations of writing again at the like rate.

And having said thus much as to the Reasons of my penning the following Discourse, I must adde something, though but little, touching the Manner of it; Wherein I hope I have not much, if at all, swerv'd from what I propos'd to my self, namely, to give an Example of Disputing in Print against a Provoking, though unprovoked, Adversary, without Bitterness and Incivility, and without pursuing those things which how much more soever they belong to the Person of an Antagonist than to his Cause, are wont to make up a great part (if not the greatest) of Books divulg'd on such Occasions. But since I intend what I write for Intelligent and Ingenious Readers, I dare expect that my forbearing to insist on such things as I judg'd wholly extrinsecal to the Opinions and Arguments I examine will be ascrib'd to the true Cause, That my Discourse will not be thought to have the less of Reason for having the less of Passion; and (especially) That my silence as to those things that are spoken to the Disparagement of the Illustrious Company that meets at Gresham College, will be look'd upon onely as an effect of my judging it fit to leave them the full Liberty to right themselves, if they think it worth while, by some better Pen than mine. And if Mr. Hobbs think fit to say any thing to the following Discourse, it will not be amiss that his Reply be as inoffensive as I have endeavour'd to make my Examen. For having dispatch'd as much as I think requisite to say of this Controversie my self, and having other (and I hope better) Employments for my leasure hours, if I can get any; I must leave the further Disputes, if any shall arise, to be manag'd by others, who, if Mr. Hobbs refuse to imitate my way of writing, will possibly make no seruple to imitate his, and put him in mind of that Law of Vespasian, upon which himself would be thought to ground that heap [Page] of strange Titles he bestows upon the two Learned Savilian So go your wayes (speaking to Doctor J. Wallis and Doctor S. Ward) you uncivil Ecclesiasticks, Inhumane Divines, Dedoctors of Morality, unasinous Collegues, Egregious pair of Isachar's, most wretched Vindices and Indices Academiarum; and remember Vespasians Law, &c. Mr. Hobbs Lesson 6. page 64. Professors, That it is unlawfull to give ill Language first, but civil and lawfull to return it. I have but one thing more to adde; which is, that I would not be so far mistaken, as to be upon the Account of what I have written against my two Adversaries, look'd upon as a Person wedded to his Opinions: For not having hitherto learn'd that either of their Books has yet made Proselytes, I presume it will not be wonder'd at that they have not made me one. And though the two Learned Authors I have answer'd, have given me no Cause to retract any of my Opinions; yet as 'tis not improbable that others reasoning upon better Principles may do what these have not done, so I am still of the same temper I was of when I us'd to propose my Thoughts but as Conjectures.

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AN EXAMEN Of the greatest Part of Mr. HOBBS's DIALOGUS PHYSICUS De Natura Aeris.

CHAP. I. The Occasion and Scope of the present Treatise.

MEeting the other day with a Treatise then newly publisht by Mr. Hobbs, and intituled Dialogus Physicus De Natura Aeris; The Name of the Author, the Subject of the Book, and the Information I had a good while before received from his Friends that he was writing against me, invited me to peruse it as a Discourse wherein I might probably find my self concern'd: nor was I deceived in my Expectation. For having cursorily pass'd through it, I readily found, that though I be not expresly nam'd there, and though some things in the Title-page, and some others in the Book it self, seem to make the chief Design of it to be the Disparagement of the Society that is wont to meet at Gresham College; yet the Arguments are for the most part levelled at some Writings of mine, published some of them the year before, and some of them this last Spring; As the Experiments, whose Explications he is [Page] pleased to censure, do all along declare. I confesse I was somewhat surpriz'd to find that Mr. Hobbs, whom if my Books have at all mentioned, it has been with respect, should fall upon a person that had not provoked him, whilst such Mathematicians as Dr. Wallis, Dr. Ward, Tacquet, and Moranus (Men much too famous to be despicable Adversaries) having a good while since professedly and unchalleng'd written against him, he hath yet, the whole Discourses of some, and so great a part of the Objections of the others, to reply to. And it somewhat added to my wonder, that a Writer of Politicks should causelesly and needlesly, for ought I can learn, fall upon a Society, whereof, besides many other Persons of Quality and men of Parts, his own great Patron, and my highly Honour'd and Learned Friend, The Earl of Devonshire himself, is an Illustrious Member. And as for me, I shall not scruple to confess, that I could have been well enough contented Mr. Hobbs had spared this Dialogue, partly because I have a natural Indispos'dness to Contention, partly because I am at present distracted by store of other Employments both of a Publick and a Private nature, (and particularly by the publishing of three or four Books of differing Subjects, and Printed in several places) partly because Mr. Hobbs's Objections are of such a Nature, that perhaps my Replies, though as short as (my Design mention'd in the Preface considered) I can conveniently make them, will amount to a longer Discourse than most Readers will think the Objections needed; and partly too, because Mr. Hobbs is pleas'd to write of divers Worthy and Learned-Men in so depreciating, and of himself in so differing, a way, that I fear I shall find it somewhat uneasie to retain (under such Provocations to decline it) the Civility I am wont, and am desirous to write with; and that I must almost despair of dissenting without an absolute Rupture from a Person, whose way of Discoursing is such, that though I shall not give it any Epithete, yet I confess it leaves me but little hope that I can oppose him without angering him.

[Page]But however, because if I can (as I intend to do) so far comply with my Inclinations and my Custom, as to wave personal and extrinsick Matters, and restrain my self to the Examen of the Argumentative part of his Discourse; My Reply will not need to be prolix; and because he has vouchsafed rather to single out a young Writer, whose Books (at least of Matters Philosophical) do but begin to appear in the World, than to defend himself against those Illustrious Enemies, upon whom he might expect to gain much more Honour; and because Mr. Hobbs's Name may with some Readers give his Arguments an Efficacy which their own Nature could not confer on them; I must resolve to submit to what he and my Concern for the Truths he rejects impose upon me. But to shorten as much as I can a Work to Which I can allow but very little time, it will be expedient before I descend to the Examination of Particulars, to premise three or four Advertisements touching the Occasion and the Nature of the Controversie, that I might not be reduc'd to a frequent and unwelcome Inculcation of the same things.

CHAP. II. Of some mistakes of Mr. Hobbs touching matters of fact, and the Author's Doctrine.

ANd first, whereas Mr. Hobbs is pleas'd to write as if the Explications and Experiments to be met with in the Physico-Mechanical Treatise he censures, were those of the whole Society at Gresham College; I must do them that Right to declare, that this way of Proceeding is manifestly grounded upon a Mistake. I will not affirm that the Mistake was wilsull, that Mr Hobbs might give himself a pretence to Quarrel with them, (who have hitherto suspended the Declaring themselves as a Society) in the controverted Points. But there are some that think Mr. Hobbs might very easily have avoided this mistake: since the Book he censures was published (and perhaps taken notice of by most of the Virtuosi here) [Page] some Months before the Society was begun. And the Experiments themselves had been long before the Book came sorth, not onely seen and discoursed of by divers Learned Men and Illustrious Persons, but had the Honour to have our great Monarch of the Virtuost, as well as of Great Britain, for a Spectator. And though possibly divers of the Learned Members of our Assembly may have no unfavourable opinion of what I have delivered in that Book; yet the Assembly, as such, has been so far from Adopting or Owning my Opinions as theirs, that it has with Approbation been propos'd among them, to repeat the Experiments, and take a review of the Explications, that upon a strict Examen of the several Opinions, and the Objections that could be brought in against them, they might see what Judgement will be fit to be past on them. And although there be very few Philosophers whose Parts may make their Judgement more formidable to me; yet to comply with their Design, whatsoever the event might be, I presented them the Engine it self, I had made use of and describ'd in my Book; chusing rather to undergo their Censures, than want their Instructions. By which it may appear, upon how little ground Mr. Hobbs has thought fit to impute to the Society those Opinions which (how Erroneous soever he is pleas'd to think them,) I must own to be mine. And this Justice I the rather do It, because 'tis all that I am to do in this Treatise on their Behalf, not onely for the Reasons above intimated, but because the Vindication of such an Assembly against Mr. Hobbs deserves a better Pen than mine, though it doth not need it.

Secondly, undertaking then the Defence of my own Cause, without Interessing them in my Quarrel, I must next admonish the Reader, that whereas Mr. Hobbs writes, as if the new Experiments were devised or at least employ'd, to prove a Vacuum; he is in this likewise mistaken. For neither has the Society declared either for or against a Vacuum, nor have I: Nay I have not only forborn to profess my self a Vacuist, or a [Page] Plenist, but I have in a fit place of my Epistle expressly said, that I reserv'd the declaring of my own Opinion touching that Point to another Discourse (which as yet is not published.) Wherefore Mr. Hobbs either injures or mistakes those, whom he will needs make his Adversaries, when he represents the new Experiments as Demonstrations alledg'd by profess'd Vacuists to disprove the Fulness of the World. And though I shall be oblig'd in the following Discourse to reject Mr. Hobbs's Supposition of a Plenum; yet I intend not thereby to declare whether or no I do absolutely allow a Vacuum. But that which I drive at, and which alone my present Work exacts, is to shew that I may reasonably oppose the Hypothesis of a Plenum, as it is stated by Mr. Hobbs: and consequently, unless he had better prov'd it, I may very well refuse to let Him take it for demonstrated. But I intend not to question whether or no other Plenists may not have better Arguments than his Principles have suggested to him: nor to deny but that the Cartesians, may without granting a Vacuum, give a more plausible Account (whether true or no) of divers of the Phaenomena of our Engine, if they will add, as some of them of late have done the Spring of the Air to their Hypothesis, That the Celestial Matter of which the Air does in great part consist, is subtile enough freely to pass through the Pores of the closest Bodies, and even Glass it self.

As for the Assertion Non dari vacuum, though, as I said, I need not in this place declare my self either for or against it, yet I confess I do not find that Mr. Hobbs, though all along this Discourse he argues from this Principle against those he thinks Vacuists, has demonstrated it. For in his Book De Corpore (though a main part of it depend Cap. 26. Sect. 2. upon the Plenitude of the World) He has that I remember, but one positive Argument (indeed he thinks that unanswerable) to evince it. And that is drawn from this Experiment: That if a Gardeners Watering-Pot be fill'd with Water, the hole at the top being stopt, the Water will not flow out at any of [Page]the holes in the bottom: But if the finger be removed to let in the Air above, it will run out at them all; and, as soon as the finger is applied to it again, the Water will suddenly and totallay be stayed again srom running out. The cause whereof (subjoyns he) seems to be no other but this, that the Water cannot by its natural endeavour to descend drive down the Air below it, because there is no place for it to go into; unlesse either by thrusting away the next contiguous Air it proceed by continual endeavour to the hole at the top, where it may enter and succeed in the place of the Water that floweth out; or else by resisting the endeavour of the Water downwards penetrate the same, and pass up through it.

But this Experiment, as an obvious one, and without dreaming that Mr. Hobbs had laid such stress upon it, I have incidentally answer'd in what I say in two or three passages on the thirty third Experiment of my Epistle. But after found that it had been more fully answer'd (but upon Grounds some of which I do not need) by my Learned Friend Dr. Ward, with whom I thus take Mr. Hobbs his Argument to pieces. The Cause, according to Mr. Hobbs, of the Suspension of the Water in the Vessel is, that the Water cannot thrust away the Air. 2. And it cannot thrust that away unless Air succeed in its place. 3. But Air cannot succeed in its place, unless either by getting in at the upper Orifice, or at the Holes that perforate the bottom. By which view of the Argument it appears that the main force of it lies in the second Proposition; but neither doth he demonstrate that (which omission might excuse us from any further Answer) nor indeed do I think it true. For if the Watering Pot were tall enough, what Reason is there, why the Water should not run out at the Holes of it? as Monsieur Paschall's Experiment mentioned in my Epistle manifests; That though in a Glass-Tube Hermetically sealed at one end, and several times as long as a Watering-Pot, the Water will not fall down; yet it will, if the Tube exceed two or three and thirty foot, or thereabouts. [Page] And indeed the Suspension or Descent of the Water depends upon the Proportion betwixt the weight of the Aqueous Pillar that tends downwards, and the Resistance or Pressure of the Air that can come to bear against it. For as on the one side, when the height of that Pillar is so increas'd, as that it can outweigh the Atmospherical Cylinder that opposes its Descent, 'twill flow out till those two Cylinders come to an AEquilibrium: so on the other side if instead of increasing the length of the Cylinder of the Water, you lessen the pressure and resistance of the Air, the Water will likewise descend, though the Pillar be very short, as I have shown in the nineteenth Experiment; where by withdrawing some of the Air, in the Receiver, and thereby weakning its Spring, the Water in a Tube Hermetically seal'd at one end of but about four foot long subsided about three foot, though That the space relinquish'd by the Water was not full of Air, as Mr. Hobbs his Argumentation requires it should be, may be prov'd by what is there added, That by letting in the outward Air when the Water was sunk so low it was immediately impell'd up again to the higher parts of the Tube.

And indeed (as I elsewhere discourse) it seems In some Dialogues of Heat and Flame. to me a difficult matter for those that reject, as Mr. Hobbs justly does, that Conceit of Natures Abhorring a Vacuum, and making it, as it were, her business to hinder it, to prove there can be no Vacuum at all by any particular Experiment. For if the Fulness of the World be not made necessary either by the Nature of Body in general, or by the Design of the Author of the Universe, it can scarce be easie to prove by a particular Experiment, that no Humane Force or Art can contrive a way of overcoming at least for some time, and as to some space, either the Gravity of fluid Bodies or whatever other Quality of the Air or Water it is by which the Contiguity of the neighbouring Parts of the World is wont to be maintain'd. As we see the Water that will not descendeven in a Tube of thirty foot, (and thereby has made [Page] men think it will never descend whilst the Air is not permitted to succeed it,) may by our Engine be brought to subside in a Tube of about a foot long. And I shall here add this out of my (yet unpublisht) Dialogues of Flame and Heat: That whilst onely particular Experiments are brought to assert the Impossibility of a Vacuum, perhaps the Vacuists will have the Advantage on their side. For a thousand Experiments are not of that force to prove universally that a thing cannot be effected, as one that shews it may be, is to prove the contrary. And the Vacuists have as well as the Plenists store of Experiments on their side that seem to favour their Hypothesis, according to which, were it true, I see not why they may not solve the Objections drawn from either the ascension of Liquors upon Suction, or the non-descension of Liquors in Watering-Pots clos'd at the top, or from any of the like Experiments I have yet met with, in case the Weight and Spring of the Air be taken in to solve the Phaenomena. And the Vacuists will have this Advantage, that if Mr. Hobbs shall say that it it as lawfull for him to assume a Plenum as for others to assume a Vacuum; not onely it may be answer'd, 'tis also as lawfull for them to assume the contrary; and he but Barely Assuming, not Proving a Plenum, his Doctrine will still remain questionable. But I think I could say more in favour of the Vacuists Experiments; namely, That whereas in some Phaenomena of the Torrecellian Experiment, and in many of those of our Engine, Mr. Hobbs proves the space deserted by the Quicksilver or the Air to have no Vacuity, because according to his Supposition the World is full; and not by any sensible Phaenomena that prove the Space in Question to be perfectly full:) For no less Fulness is requisite to the truth of his Hypothesis:) The Vacuists on the other side need not go about to prove that those Spaces are not full by their Hypothesis. But they prove it by this, that it appears by sensible Phaenomena, that the Quicksilver deserts the upper part of the Tube; and that much Air is pump'd out of our Receiver. (The first of which is evident [Page] to the Eye; and so is the other too, when the Pump is kept under Water.) But it does not appear by the like Phaenomena, that the Air (as Mr. Hobbs would have it in is Elements) does Succeed to fill, I say, perfectly to fill the deserted space; which also they will confirm from hence, that in the Torrecellian Experiment by inclining the Tube the relinquish'd space may be again readily fill'd with Mercury; and if our exhausted Receiver be plung'd under Water, that Liquor, when access is given it to the Cavity, violently rushes into it, and almost fills it up.

From all which it seems probably deducible, That 'tis a very hard thing, by. Mr Hobbs's way of managing the Controversie, to prove that there can be no Vacuum, But as for the Cartesian's more subtile and plausible way of asserting a Plenum, it concerns me not here to Dispute against it, or Declare for it.

I will add this, and but this, on the occasion of Mr. Hobbs's Building a great part of his Philosophy upon no surer a ground, That we may hence learn how little Reason there is to blame me as he is pleas'd to do, for making elaborate Experiments; and that though (as I have elsewhere purposely and amply discours'd) obvious Experiments are by no means to be despis'd; yet 'tis not safe in all Cases to content ones self with such: Especially when there is Reason to suspect that the Phaenomenon they exhibit may proceed from more Causes than one, and to expect that a more Artificial Trial may determine which of them is the true.

Thirdly, whereas Mr. Hobbs is pleas'd to find much sault with the Society, and me, for not assigning the Case of Springs in general; that Omission seeming to him very unworthy of Philosophers: I answer, that the Society having hitherto, for weighty Reasons, forborn to determine the particular Causes of Things, there was no Reason they should alter their Method, for Experiments that were not made or published by Them or by their Order And as for me, the Title of my [Page] Book promises some Experiments touching the Spring of the Air and its Effects, not Speculations of the Causes of Springs in general. My avow'd Intention was candidly to communicate with the Curious some Experiments which I thought their Novelty would render acceptable to them, wherein I have the good luck not to have been mistaken; nor can I be justly censur'd for not performing what I did not undertake, nor was oblig'd to. And perhaps Mr. Hobbs would more prejudice the Commonwealth of Learning by his severity, than he has yet Advantag'd it by any other way, if he could obtain, that none should publish an Experiment or Observation that cannot by deduction from the First and Catholick Principles of Philosophy assign the true Cause of it. But when I take upon me to write, as Mr. Hobbs has done, Elements of Philosophy, then perhaps I shall be able to give an Account of Springs, not much more unsatisfactory than others think his. For though he referre us to his Explication given of the Motion of Restitution in his Book De Corpore; yet in the 22 Chapter and 30. Section, which professedly contains his Theory of it, after having premis'd, (what rightly interpreted may be true enough,) that the Cause of the Restitution proceeds not from the taking away the force by which they were compressed or extended the (removing of Impediments not having the Efficacy of a Cause) that which follows to the end of the Section is onely this: The Cause therefore of their Restitution is some Motion either of the Parts of the Ambient, or of the Parts of the Body compress'd or extended. But the Parts of the Ambient have no endeavour which contributes to their Compression or Extention, nor to the setting them at Liberty or Restitution. It remains therefore, that from the time of their Compression or Extension, there be left some endeavour (or Motion) by which the Impediment being remov'd, every Part resumes its former place; that is to say, the Whole restores it self. Now this notwithstanding, I am so dull, or so wary, that though I had met with this passage, and all the Praises the Author in his [Page] Dialogue gives it, yet I should have made some scruple to undertake the assigning the true Cause of Springs in general. For first, the Learned Gassendus, and the Epicureans both Ancient and Modern, together with divers other Naturalists, do not admit what Mr. Hobbs supposes a few lines before, that That which is at rest cannot be mov'd but by a moved and contiguous Movent. For they think Motion, or at least conatus ad motum, an unlooseable Property, congenit to Matter. And, by the way, whatever exceptions I have to this Opinion, yet I am not satisfied with that Principle of Mr. Hobbs, though it be the Fundamental one of his Philosophy; unless it be more warily propos'd. For to assert universally and without exception, as he does in his Elements, that nothing can be moved but by a Body contiguous and moved; I do not take to be true, nor consistent with his other Assumptions. This I elswhere (in a Discourse against another than Mr. Hobbs, about the Christian Religion) prove more at large: But now it will suffice to represent that Mr. Hobbs not onely admitting, but making use in his Philosophy of the Creation of the World, either he must allow that Motion is Natural to some, if not all Parts of Matter; or that God put them into a Motion not included in their Nature. From which it will necessarily follow, that at least some Bodies may have Motion though it be not given them by any Body contiguous and moved, as an attentive considerer m [...]y easily discern. But to return to the Cause of Springs. Secondly, whereas Mr. Hobbs assumes that the Parts of the Ambient have no endeavour which contributes to their Compression or Extention, nor to the setting of them at Liberty or Restitution: He says this indeed, But does not go about to prove it. And I should the less have made this precarious Assertion, because that after the celebrated Des Cartes himself, the Cartesian Philosophers generally ascribed the Motion of Restitution to the passage of a subtile Ethereal Substance (and an AEther Mr. Hobbs also admits) through the Pores of the Springy Body, which striving to [Page] obtain its wonted Freedom of passage, restores them to the shape and bigness from which they were forced. Nay, I shall have occasion to shew anon that Mr. Hobbs himself, whatever he say in this place, does elsewhere ascribe a Motion of their own to multitudes of Terrestrial Corpuscles. And I might add, that elsewhere he speaks of the re-kindling of the Fire taken out of the Receiver after this manner.

Quanquam vis illius motus in Recipiente (ut loquimini) Pag. 18. evacuato diminuta sit, oppressa ab Aëris intus commoti consistentia, non tamen extinguitur; & propterealevata oppressione, satis habebit virium ad excitandum phantasiam lucis quanquan debiliorem. But I shall rather subjoyn, That yet, Thirdly, I do not think it improbable what the Learned Gassendus had taught, and what Mr. Hobbs here teaches, that the Restitution of bent Springs may proceed from a certain Endeavour or Motion in their internal Parts (left from the time of their Compression or Extension) which when the Impediment is remov'd, makes every Part resume its former place, and thereby makes the Whole restore it self. But this notwithstanding, I fear'd others might be as Inquisitive as my self, and might expect from him that would undertake to settle a general Theory of the Motion of Restitution, the clear and distinct Explication of several Phaenomena that I had met with, which are not touch'd, nor perhaps were, some of them, thought upon, by Mr. Hobbs. As first, why such a de [...]rminate Temper of Iron and Steel is requisite to make it Elastical; so that if after having been hardned and gradually heated it be suddenly cool'd at an inconvenient point of time, it will be brittle, and fit to make Gravers and other rigid Tools, not Springs. Next, why Bows and other Elastical Bodies, if they be kept too long bent, lose in process of time almost all their Elastical Power, and continue crooked. Thirdly why not onely divers solid Bodies as well as Lead and Gold, which before tryal, one would think as likely as many Springy ones to have their Parts put into a due Motion by the force that bends them, [Page] should be devoid of an Elastical Power. Fourthly, what kind of Motion, and what kind of Texture it is, by virtue whereof, the Parts of a Body being for a very short time put into Motion, do some Months, perhaps some Years, retain in great part a smart Motion, without in so long a time communicating it to the Ambient Bodies, to some or other of which multitudes of them are perpetually contiguous, and thereby losing it themselves. Why upon such a bare and inartificial change made in the Texture of a Body as is scarce at all discernable to the Eye, it should acquire a strong Spring that it had not before (as I have try'd upon Silver and Copper, which though flexible before they were hammer'd, yet being beaten into thin Plates obtain'd a notable Spring:) And why (which may seem more strange, upon another light change of Texture) the acquired Spring may presently be lost again; as I have try'd in Silver, that Chymists teach us loses nothing in the fire, which having by being hammer'd acquir'd a strong Spring, we have presently made flexible again as before, by only heating it red-hot, without so much as melting it; which argues that in Springs, Texture is as well to be considered as Motion. To these I might add other Particulars that I had either made or observ'd (and mention in another Treatise) concerning Springs; all which Phaenomena perhaps every one that has read what we have lately recited out of Mr. Hobbs, will not presently be able satisfactorily to explicate. So that I hope the equitable Reader will not think it a fault that (contenting my self to propose the two Explications of Springs, I saw most lik'd among the Curious; to which I should have added Mr. Hobbs's, if I had found it as much esteemed) I declin'd engaging my self in Controversies about the Origine of Motion, and such other high Speculations, as had my Abilities enabled me, neither my Design exacted, nor my leasure permitted that I should prosecute. And though Mr. Hobbs be pleased to speak thus of his Notion concerning the Restitution of Bodies; Sine qua Hypothest quantuscunque labor, ars, sumptus, [Page]ad rerum naturalium invisibiles causas inveniendas adhibetur frustra erit: Yet whether that Pag. 8. bold Assertion should passe for an Argument, for an Hyperbole, or for a Complement to himself, I am content to let the Reader judge.

Fourthly, Mr Hobbs in divers passages wherein he disputes against me, seems to have misapprehended my Notion of the Air. For when I say, that the Air has Gravity and an Elastical Power, or that the Air is, in great part, pump'd out of the Receiver, 'tis plain enough that I take the Air in the obvious Acception of the word, for part of the Atmosphere which we breath, and wherein we move. Nor do I find that any other of my Readers do otherwise understand me. But Mr. Hobbs seems to think he has sufficiently confuted me, if in some cases he have prov'd (which whether he have done well or no is not here to be examin'd) that there is a subtile substance, which he calls AEther (but which I wish he had better explain'd) in some places which I take not to be fill'd with Air; and that the AEther has or has not some Accidents which I deny or ascribe to the Air. Whereas I deny not but that the Atmosphere or fluid Body that surrounds the terraqueous Globe, may, besides the grosser and more solid Corpuscles wherewith it abounds, consist of a thinner Matter, which for distinction sake I also now and then call Ethereal. And therefore though I did not think my self oblig'd to declare against either the Atomical or the Cartesian Hypothests touching the Nature of the Air, yet I propos'd the later too as probable (which as it excludes a Vacuum, so it makes the Air consist in great part of a Celestial Matter.) And my incidental Explications of the Rarefaction and Condensation of the Air, together with my comparing it to a Fleece of Wooll, sufficiently declare that I take it not to be a Homogeneous Body; and though there be Air intercepted betwixt the Hairs of Wooll, yet in case I should prove that a Box were not so full of Wooll as before, because the most part of the Hairs had been taken out, I should [Page] not think he argued well against me, that should onely prove that the Box contain'd as much of Matter, consisting of Air and Wooll together, afterwards as before. Nor do I think Mr. Hobbs has in divers passages, wherein he supposes he disputes against me, much more directly contradicted what I teach concerning the Air, if that word be rightly and in my sense understood. And on this occasion I must crave leave to add, that whereas he is pleas'd to intimate that I misrepresent the Cartestan Hypothests, ascribing that to the Air which Des Cartes does to Water; If the Reader think it worth while to compare the Summary Account I give of that Hypothests, with what Des Cartes himself has taught in his 45, 46, & 47. Articles of the fourth Part of his Principles, wherein that Author comprises his Doctrine of the Nature of the Air, he will quickly find, that whether or on Mr. Hobbs be mistaken, I am not unless it be in estimating his Hypothests by what he teaches in his Principles, which were published after his Meteors, and more elaborately written. And as for that particular, which alone Mr. Hobbs alledges, namely, that he makes not the Parts of Air but of Water so flexible: Des Cartes's Words in the 46. Article are these; Cum ejus Particulae ferè omnes sint flexiles in star mollium plumularum veltenuium funiculorum, &c. And as for what Mr. Hobbs subjoyns, Sed quisquis talis supposition is Author fuit, parum refert. Nam ipsa Hypothesis, in qua motus supponitur materiae subtilis sine causa velocissimus, & praeterea Corpusculorum innumer abiles vertigines diversae ab illius Materiae unico motu generatae, vix sani hominis est. I cannot but in Gratitude to such a Personage declare my dislike, to find him upon so slight an Occasion so coursly us'd for an Opinion the Censurer of it does no better confute, and Which is thought to be in some particulars not so unlike his own. And perhaps I should be afear'd that Mr. Hobbs's speaking so severely of one that was at least a famous Geometrician, might reflect upon the English Civility in the opinion of Strangers, if I did not hope that those who have read Doctor Ward's [Page] Exercitation will look upon this censure of the Cartesian Doctrine by Mr. Hobbs, as provoked by that severe Judgment of Des Cartes mentioned by the Doctor in these words; Nempe hoc est quod alicubi admiratus est Wardi Exer. in Philosoph. Hobbian. pag. 188. magnus Cartesius; nusquam eum, sive verum, sive falsum posuerit, rectè aliquid ex suppositionibus, ratiocinando inferre.

CHAP. III. Wherein the Weight and Spring of the Air are asserted against Mr. Hobbs.

HAving thus dispatch'd those general Considerations I thought expedient to premise, my proposed Method leads me in the next place to consider that Mr. Hobbs does not, that I remember, deny the truth of any of the matters of fact I have deliver'd. Nor does he, if my memory fail me not, labor to prove that the Explications I have given of my Experiments, are not agreeable to the Doctrine I propos'd: But rather thinks fit to reject our two grand Hypotheses themselves, The Weight, and the Spring of the Air. And therefore it will suffice us in this Chapter briefly, but not slightly, to prove what he is unwilling to grant.

And first, that the Air (in the sense wherein we take the word) is not devoid of Weight, we have prov'd by divers Experiments: which having more fully deliver'd in the Book it self, it may in this place suffice now to name them.

One then of these Experiments that prove the Air's Gravity, is, that we found a blown Bladder carefully weighed in an exact pair of Scales, manifestly heavier when full of Air, than when the Air was let out.

Next it has been observ'd in our 36. Experiment, that an AEolipile, being well heated, and the little hole left at the top of the Pipe being stopt, when it was thus hot; upon the opening of that hole, when the AEolipile was grown cold again, the external Air rushing in with a wistling noise at [Page] the foremention'd Orifice, made the AEolipile weigh so much more than it did just before the external Air got in, that it amounted, by computation, to near a thousandth part of the Weight of an equal bulk of Water. And though some difficulty may perhaps be mov'd touching the accurateness of the proportion this way found out, betwixt the gravities of those Bodies; yet that the one as well as the other is actually heavy (which is all that we here need contend for) the Experiment sufficiently manifests.

Thirdly, in the Magdeburgick Experiment, (mention'd at the beginning of our Epistle) the ingenious makers of it found, that, having before weighed the great Receiver they were to exhaust, and having done the like after the extraction of the Air, they found it to weigh one whole Exper. Magdeburgicum apud Schotum, pag. 446. Ounce and 3/10; quod sane (saies the learned Publisher, though a Peripatetick) luculentissimum est argumentum gravitatis aëris.

Fourthly, in our 36. Experiment we relate our having weighed the Air, and that shut up in Bodies in our exhausted Receiver, wherein of two Bodies of differing Natures (the one a blown Bladder, and the other a Glass Bubble) that were aequiponderant each to a more solid Weight before the Air was pumpt out, that which included a good quantity of Air did manifestly preponderate after the exhaustion.

And to these four we might adde other proofs to the same purpose; But that these contain in them such a variety of Cases, that I think it would be superfluous.

But now let us see what Mr. Hobbs objects against the newlymention'd Experiment of the Bladder weighed in the exhausted Receiver, (for the others he quarrels not with,) Quod quidem lanx (saith he) in qua est vesica, magis deprimitur Pag. 15. quam altera, certi esse possunt, oculis testibus: Quod autem id à gravitate aëris naturali accidit, certi esse non possunt; praesertim si quae sit gravitatis causa efficiens nesciunt. But I know not whom Mr. Hobbs will perswade, that a man cannot be [Page] sure that Lead is in Specie heavier than Cork, unless he knows what is the efficient cause of Gravity. And Mr. Hobbs speaks in his 30. Chapter (where he expresly treats of that Subject) as if that had not been explain'd by any man, and consequently not by any Writer of Staticks: (and perhaps I am therein somewhat of his mind) And yet sure all these Writers, treating of the Proportion of Heavy Bodies, did not write they knew not what. And, though he mentions his own Hypothesis, as that than which nothing is more likely; yet I think I could frame Objections against it, that would not easily be answer'd, if my present task requir'd it; or if I found his opinion, in this point, embrac'd, as yet, by men of Note. Wherefore I shall now say no more of it than he himself doth namely, that according to his Doctrine, It may well be thought to determine (for it is a certain consequent) that heavy Bodies descend with less and less velocity, as they are Elem. of Phil. Ch. 30. Sect. 4. more and more remote from the AEquator; and that at the Poles themselves they will either not descend at all, or not descend by the Axis: which whether it be true or false, Experience must determine. Which till it have done in his favour (an event I do not expect) I hope he will allow me to distrust his Hypothesis.

But to return to our Experiment. The Account he gives why the Bladder does propend (for so he loves to speak) is this, Quod vesica sive follibus sive flatu oris Pag. 16. distenta sit, gravior sit quam eadem vesica non distenta, negarenolo, propter majorem quantitatem Atomorum follibus, vel Corpusculorum fuligineorum ab halitu inflatorum. Ab experimento autem quod fit à vesica inflata nihil colligunt quod sit satis certum. Oportuit lancibus imponere duo vasa pondere aequalia, quorum alterum esset accuratè clausum, alterum apertum: Sic enim non inflatus sed inclusus tantum aër ponderatus esset. Quando igitur aërem sic ponderatum videbis, meditabimur postea quid dicendum sit de Phaenomeno quod retuleris. But, as to the First part of this passage, it does not deny the gravity of what we call the Air; but onely endeavours [Page] to shew what Parts they are that make it heavy. And as to the Second, he seems to mistake the present Case. For, there is no need that the Air in the Bladder be, before the exhaustion of the Receiver, (in which the foregoing (fifteenth) Page declares he Supposes the Experiment to be made) heavier than the outward Air. Wherefore when he subjoyns that from this Experiment we collect nothing quod sit satis certum, the Affirmation is not an Inference, but Precarious. And as for the annexed way whereby he would wish to have an Experiment made fit to infer the gravity of the Air, if he had not. over-look'd what I have delivered in the beginning of the 36. Experiment, he would easily have perceiv'd that we did make a Trial much of the same nature with that he desires. For we weighed in our Receiver the Air, in a Glass Hermetically sealed; wherein it was not (to use his Expression) inflated, but onely included. This is what he here objects against the gravity of the Air in the other place (Pag. 8. & 9.) where he saies something to this Controversie; he inculcates also that we should first explicate what is Gravity, and then adds, Quod Atmosphaerae insunt permistae corpori AEthereo multae tum aquae tum etiam terrae particulae, facile persuadeor; Pag. 9. sed quod in medio AEthere, sursum, deorsum, quaquaversum motae, nec semper alterae alteris innitentes gravitent, inconceptibile est. To which he adds two or three Reflexions, whose Examen being here unnecessary, would require more time than perhaps it would (in reference to the present Controversie) deserve: for we are now enquiring not how the Air comes to gravitate, but whether or no it have gravity. And since in his Elements of Philosophy he grants, and gives Chap. 30. Sect. 10. his Reason for it, That if Air be blown into a hollow Cylinder, or into a Bladder, it will increase the Weight of either of them a little: and since here he likewise confesses (as we have just now seen) that there are mingled with the AEther many aqueous and earthly (and consequently heavy) Particles: he confesses that which we labor to evince; namely, that the [Page] Air is not devoid of Weight. And it concerns us no more than himself, to shew how the Corpuscles, upon whose account the Air is heavy, make it so. And this being what Mr. Hobbs in several places thinks fit to object against the Gravity of the Air; the Reader will, I suppose, easily take notice that he has left the Experiment of the AEolipile, and some others, unanswered. Though these alone prove that the Air is a manifest Weight even when it is not comprest, but retains its laxity. Having said thus much to evince against Mr. Hobbs the Gravity of the Air, let us now examine whether it have not also a Spring (in the sense we take that word in.) This though Mr. Hobbs be pleas'd Utraque enim illa phant sia tum gravitatis Atmosphaerae, tum vis Elasticae sive antitupiae aëris, somnium erat. Dial. p. 21. to call (as he also does the weight of the Air) a Dream; yet he does himself grant, in effect, as much as is requisite to prove the Spring of the Air, in the sense I contend for it. For taking upon him to give account (how good an one we shall see anon) of that known Experiment wherein the Air is comprest in a Glass Bottle by the forcible injection of Water, which Water, when the Glass is unstop't, the Air does again throw out in recovering its former Dimensions; of this Experiment (I say) he gives this account (Pag. 24.) Aër quo ab initio Sphaera plenus erat à Corpusculis illis terreis motus motu circulari simplice, vi injectionis coactus, qui quidem purus est exit (aquam injectam penetrans) in aërem extrinsecum, locum relinquens aquae; sequitur ergo Corpusculis illis terreis minus relinqui loci in quo motum suum naturalen exercere possint: itaque in se mutuo impingentes aquam urgent ad egressum; egredientem aër externus (quia universum supponitur esse plenum) penetrat, locumque egredientis aëris successivè occupat, donec Corpuscula, quantitate aëris eadem restituta, libertatem motui suo naturalem recipiant.

But how little this comes short of granting as much Spring to the Air as the Cartesians do, and as I need require, may easily be judg'd by divers passages in our Book; and particularly [Page] by our proposing as not improbable, the Cartesian way of explicating the Spring of the Air; according to which the Corpuscles that swim in the AEther, being each hindred by the neighbouring ones from the freedom of its motion, they beat off one another (which Mr. Hobbs would have them do:) whence it comes to pass that, in any assign'd portion of Air here below, the Corpuscles that compose that portion, beaten off by one another, do make the whole portion tend to obtain (though not exactly to fill up) more room, and consequently to emulate a Spring, like that which we scruple not to ascribe to a comprest Fleece of Wooll, because of a like endeavour to expand it self.

We may enforce this by another passage of Mr. Hobbs's, that speaks expresly enough to our present purpose, where he gives this Reason of one of the Phaenomena of our Engine, Quoniam per suctoris retractionem aër purus impulsus Pag. 11. erat, partes autem terreae impulsae non erant; major erat ratio particularum terrearum quae extra Cylindrum suctori contiguae erant, ad aërem purum, in quo motum suum exercebant, post revulsionem The Motions therefore of those small Bodies (speaking of the Earthy Particles in the Air) will be less and less free, by how much the quantity of the injected Water is greater and greater: so that by their Motion falling upon one another, the same Bodies will mutually compress each other, and have a perpetual endeavour of regaining their liberty, and of depressing the Water that hinders them. Elem. Chap. 30. Sect. 9. quam ante: quare particulae illae motae minus habentes loci ad motum suum naturalem exercendum, aliae aliis impingebant, & propellebant: necesse ergo erat, ut particulae quae suctoris superficiei contiguae erant suctorem propellerent. To which we may adde, that Mr. Hobbs himself seems rather to reject other mens wayes of proposing the Spring of the Air, than resolutely to deny the thing it self. For, Vidisti (sayes he) jam Elastrum illud aëris quod supponunt, aut impossibile esse, aut recurrendum esse ad Hypothesin Hobbianam. Pag. 8.

But besides Mr. Hobbs's Concessions in the passages newly recited, and some others; we can prove the Spring of the Air [Page] by many of the Phaenomena of our Engine, which we have deduc'd from it, and of which he does not offer any other way of Explication. Wherefore we shall now content our selves to prove the Spring of the Air by two Experiments: The one not mention'd in our Epistle, and the other much oppos'd by Mr. Hobbs.

And first, if you make the Torrecellian Experiment in a Tube of between two foot and half and three foot in length, and if, when the Mercury rests at its wonted Station, you dexterously stop the Orifice of the Tube with your Finger (that Orifice being lifted up as near the surface of the restagnant Mercury as it can be, without giving admission to the external Air) and if then you quite lift up the Tube thus stopt into the free Air you shall feel upon your Finger little or no gravitation or pressure from the Weight of the Mercurial Cylinder, distinct from the Weight of the Tube: because (as we have more fully explicated this Phaenomenon elsewhere) the gravity of the Quicksilver In our Defence against Linus. is balanc'd by that of the outward Air that thrusts the Finger against it. But if you invert the Tube, and having let in the Air at the Orifice, stop it again with your Finger, and again let the Mercurial Cylinder lean upon that Finger; you shall then find your Finger strongly prest, and endeavour'd to be thrust away: which new pressure, since it cannot come from the Mercury, that being the very same that was in the Tubebefore, nor from the Weight of the admitted Air, which perhaps may not amount to so much as a grain, to what can we rationally ascribe it but to the Spring of the included Air, whose force will be as well manifest to the Eye as the Finger, if the Tube be unstopt under the surface of the restagnant Mercury; for then that in the Glass will not rest as before at the usual Station, but be deprest beneath it a good way, perhaps some Inches? And if you make the Torrecellian Experiment in a short Tube seal'd at neither end, but stopt above and below with your Fingers, you shall find, upon the [Page] unstopping of the upper Orifice a new and forcible pressure upon the Finger that keeps the lower Orifice stopt, made by the gravitation of the external Air, which was before kept off from leaning upon the Mercurial Cylinder by the upper Finger; the Pulp of which Finger by that gravitating Air was before thrust into the deserted Cavity of the Tube (as we have elsewhere discourst, in a fuller measure, of these Experiments.) Which will evince against Mr. Hobbs, both the Spring of the Air and Gravity of the Atmosphere; since he is as little as I for ascribing these Phaenomena to the efficacy or absence of my other Antagonist's imaginary Funiculus.

The other Experiment I shall mention is the Fourth in our Epistle; namely, that of the swelling and shrinking of a Bladder hung in our Receiver, according as the ambient Air, and consequently its pressure, is withdrawn or suffer'd to return. But though this Experiment be so congruous to our Hypothesis, that 'tis generally acquiesc'd in by those Ingenious men that have hitherto seen it; yet Mr. Hobbs is pleas'd to reject our Explication, and substitute another in these Words, which are all he has concerning this matter. Quia Cuticula omnis ex filiculis constat, quae propter figuras, contactum Pag. 19. per omnia punct a accuratum habere non possunt, pervia ergo est vesica, cum sit cuticula, nec aëri tantum, sed etiam aquae, qualis est sudor. Eadem ergo aëris per vim incussi est compressio intra vesicam quae extra, cujus conatus, propter viam motuum undiqua (que) decussatam, tendit undiquaque ad superficiem vesicae concavam. Quare necessarium est ut undiqua (que) intumescat, & crescente conatûs vehementiâ tandem laceretur. But, if this be a sufficient Answer to such an Experiment, I confess I fear it will be harder than we are yet aware of to prove any thing by Experiments.

For first, how unlike is it to be true what he affirms, and what his Reply supposes, namely, that such Bladders as we us'd are readily pervious to the Air; when easie Experience shewes us, that by leasurely compressing such blown bladders [Page] betwixt our hands, we shall rather break them (as we have try'd) than squeeze out the Air at the Pores? So that the rest of his Answer being built upon what is so repugnant to common Experience, will not need a particular Consutation: but however ex abundanti we will adde, that in our 36. Experiment, we relate that by the exhaustion of the Air we likewise broke a Glass Hermetically seal'd; and to say that Glass also is pervious to Air, were to affirm what the greatest part of his Book supposes to be false. Besides, whereas there is not any sensible and unquestionable Phaenomenon to prove that the Receiver is full of any such aër per vim incussus as he would have, we see plainly that when the Air does manifestly get into the Receiver, the Bladder is not thereby made to swell, but strangely to shrink. Moreover since (according to Mr. Hobbs) the Bladder is pervious to the Air, and the Air within the Receiver is universally comprest, as well that which is within the Bladder as that which is without it; how comes it to pass, that the Air that bears against the Convex Surface of the Bladder does not resist that which is contiguous to the Concave Superficies of the same; And at least how comes the Bladder to be broken by the Air, which, according to Mr. Hobbs, can get in and out at pleasure? And lastly, to shew that to the swelling of the Bladder there needs nothing but the Spring of the included Air, and not such vehement agitation of the ambient Air as Mr. Hobbs supposes to be made in our Engine; It appears by the elsewhere-mention'd Experiment of Monsieur Paschal, that in the free and ordinary Air a Foot-ball half blown up will swell more and more the nearer it is carried to the top of an high Mountain; where the incumbent Cylinder of the Atmosphere is shorter, and its Weight lighter: and will, for the contrary Reason, grow more and more flag'd, the nearer it approaches again to the foot of the Mountain.

Though I doubt not but the Arguments employ'd in this Chapter will be sufficient to convince impartial Readers; yet [Page] I shall adde by way of Inforcement, that whereas Mr. Hobbs ascribes the Weight of the Air in Bladders to the earthy Corpuscles intruded by him that blows them up; and attributes the Spring of the Air in the Wind gun and in the Phaenomena of our Engine, to the violent Motion the Air is put into by the vehement impulses of the Rammer or Sucker: our Doctrine may be evinc'd by Experiment, wherein the Air in its natural and wonted state operates without being forcibly comprest or put into motion by us. This may appear by the two sorts of Experiments to be made upon high Mountains, which we have mention'd and urg'd in the Second Part of our Defence against the Learned Linus. Wherefore referring the Reader thither, we shall now onely in very few words mention the substance of them.

The First Experiment is, That it has been found upon Tryal, both formerly in France and since in England, that the Quicksilver in the Torricellian Experiment falls notably lower at the top of a Mountain than at the foot, (by Monsieur Paschal's observation upon a Hill (far higher than those the Experiment was try'd on here) the difference was so great, as to amount, as the most ingenious Pecquet, a happy promoter of Experimental Learning, informs us, to above three Inches) which we say is caused by this, that the Atmospherical Cylinder is much lighter, as well as shorter, at the top of the Mountain than at the bottom: and Mr Hobbs disallows not the Experiment, but yet gives onely this account of it, Sed & particulae illae quae interspersae aëri it a moventur ut supposuimus, Pag. 12. magis confertae sunt ad radicem montis quàm in summo, nam hoc quo (que) supposuimus. But what then? how does the plenty of these interspers'd Particles hinder the Mercurial Cylinder from descending at the bottom of the Hill as much as at the top, unless by their gravity or pressure? And 'tis very unlikely that the Earthy Atomes, contiguous to the restagnant Mercury at the bottom of the Hill, should be able by their weight to keep suspended a Cylinder of Mercury of above three Inches, [Page] unless the contiguous Air were gravitated upon by the weight of other incumbent parts of the Atmosphere.

The other of the two mentioned Experiments is briefly this, That a Termoscope being carried from the bottom to the top of a Hill, the included Air, instead of shrinking in that colder Region, manifestly dilated it self, and notably depress'd the water. An effect which I see not to what it can well be attributed but to the spring of the included Air, which having not near so great a pressure against it from the Atmosphere incumbent on the restagnant and suspended water, was able to make it self more room than before it could; and since that pressure of the Atmosphere depends for ought appears upon its gravity, the same Experiment may argue both the spring of the Air and its weight.

And this may suffice for our third Chapter, wherein having evinc'd against Mr. Hobbs our grand Hypothesis of the weight and Spring of the Air, I hope we have dispatched the chief part of our work; since as for the particular Explications we deduce from these Hypotheses, there are but very few, if any, that he endeavours to prove incongruous to them. Yet after we shall have (in the following Chapter) consider'd upon what grounds he prefers his Doctrine before ours, we shall (God permitting) in two or three other Chapters gather up the things that he objects against some particular Opinions and Explications by us delivered, and examine them.

CHAP. IV. Wherein Mr. Hobbs's principal Explications of the Phaenomena of the Authors Engine are Examined.

OF the Hypotheses that Mr. Hobbs assumes to explicate the Phaenomena of our Engine, himself gives us a summary in this passage, (pag. 10.) intellêxtiergo Hypotheses meas, 1. Quod aëri interspersae sunt particulae multae terreae praeditae motu circulari simplice, naturae congenito. 2. Quod major est quantitas earum particularum in aëre propè adterram quàm in aëre à terra remotiore.

[Page]Now here I might at the beginning take notice, that there are other things which he takes for granted. As, first, Non dari Vacuum, which as we have already seen he has not well evinced, nor I think easily will upon the grounds he proceeds on. Next, that our common Air is chiefly composed of an AEthereal substance, which methinks he should have proved; since for the most part the Vacuists (and such he will needs have his Adversaries to be) admit not that pure Air of his. Thirdly, that the Air, at least the pure Air, is easily divisible into parts always fluid and always Air. Indeed he sayes of this Assumption, Pag. 4. Nec suppono tantùm, sed credo; but neither to suppose nor to believe, is to prove. And what he adds, Ioid. Ne (que) est qui hactenus ullam adduxit rationem, quare ita esse non potest; if it were true, would conclude little, since many things have not been, and perhaps cannot be, proved to be true; of whose not being possible no proof has been given. We might, I say, mention and examine these other Assumptions of our Author, but for brevities sake we will consider those two lately recited from him.

And as for the second of them, bateing the peculiar motion he is pleas'd to ascribe to the earthy Particles, I shall not contend with him about that Hypothesis; and therefore shall now onely consider the other. The Motus circularis simplex it self, which he imagines in the Sun and the terrestrial Globe, I shall not need to examine, since Dr. Ward (a person whom, wthout disparagement to a famous man, I may affirm to be ati least as esteemed for Astronomy as Mr. Hobbs) has expresly endeavoured to confute it, and that not without some derision, (which yet I willingly forbear to imitate) by Arguments that I cannot learn Mr. Hobbs has yet answered. And I am informed that the learned Dr. Wallis, and others intend, some Animadversions on this Motion. But restraining our present consideration to what this Dialogue suggests to me, This Assumption to me seems very precarious, since I know not any unquestionable Example or Experiment whereby it can [Page] be made out, that any small parcel of matter has such a motus circularis simplex as he ascribes to each of these innumerable earthy and (as himself adds in the same page) aqueous Particles. The onely Argument he brings in that page to prove that each Atome would have this motion, if all the rest of the earth were annihilated, does not to me seem clear. For, not to mention that it is still by many learned men doubted whether the Terrestrial Globe it self have it; nor to examine whether or no he assigns a good Natural cause of it; it is not always true, that each minute part of a Homogeneous body (which yet 'twill be hard to prove the Terrestrial Globe to be) has in every respect the same qualities with the whole; As the roundness which a small drop of Water or Quicksilver is commonly observed to have when it leans upon a dry or greasie plain, is not to be met with in great portions of either of those Liquors, though placed upon the same plain. And Mr. Hobbs as well as we makes the terrene Atoms in the Air to have gravity, which yet is a quality that does not properly belong to the whole Globe of the Earth; nor is it manifest why, because the Terrestrial Globe moves in a vast Circle about the Sun, each particular Atom of it must describe a small Circle in the Air about I know not what Centre. And since he teaches in his second Hypothesis, and a few lines before it, That the Air, near the Earth abounds with such Terrene Corpuscles, 'tis not likely they should be permitted to exercise such a regular motion as he attributes to them; but hitting against one another, they must in probability be put into almost as various and confused a motion as Des Cartes ascribes to his Terrestrial Particles swimming in the Atmosphere. That which some will, I doubt not, peculiarly wonder at in Mr. Hobbs's Hypothesis is, that he makes this regular motion of each Atom naturae suae congenitus: For Philosophers that are known to wish very well to Religion, and to have done it good service, have been very shie of having recourse, as he has, to Creation, for the explaining [Page] of particular Phaenomena. And the Cartesians will think it at least as allowable for them to suppose the Motion he will not grant in their Materia subtilis, as for Mr. Hobbs to assume it in his Particulae terreae: especially since he seems to make each such Atom put into and kept in a regular motion; whereas they assume but the having of one general impulse given to the whole mass of Matter. Those likewise that fancie a Spring properly so called in particular Aerial Corpuscles, will hence perhaps take occasion to think they may suppose an ingenite motion fit for their turn, as well as he an ingenite motus circularis simplex. How well like wise this Hypothesis will agree with his Fundamental Doctrine, That Nihil movetur nisi à corpore contiguo & moto, I leave to him to consider. As also whether or no Gassendus, and those other Atomists that admit Creation, may not hence countenance their grand supposition of the congenite motion of Atoms, which granted would destroy the best part of Mr. Hobbs's Philosophy. But whatever becomes of this motus circularis simplex, I need not be much solicitous, having formerly shewn, that the admission of it would not disprove what I have delivered concerning the Spring of the Air: and therefore leaving Mr. Hobbs to dispute it out, if he think fit, with his other Adversaries, I will proceed to the main Explications, wherein Mr. Hobbs endeavours to prefer his Doctrine about the Phaenomena of our Engine before ours. And these I find to be the four that ensue.

The first and principal of these is that wherein he strives to prove, That by the Exhaustion of our Cylinder no Vacuum is produced, and to give of the Experiment it self a very differing account from ours. This he does in the following passage; which, by reason of its importance in our present Controversie, we shall set down verbatim: Dum Suctor (sayes he) retrahitur, quanto relict us locus major fit, tanto minus loci relinquitur aëri externo, qui retrusus Pag. 5. à Suctore moto versus externa, proximum sibi aërem similiter[Page]movet, & hic alium, & sic continuè, ita ut necesse sit aërem tandem compelli in locum desertum à Suctore, & intrare inter superficiem Suctoris convexam & Cylindri concavam: supposito enim aëris partes esse infinitè subtiles, impossibile est ut viâ illâ qua retrahitur Suctor, illae non se insinuent. Primò enim, contactus superficierum istarum per omnia puncta perfectus esse non potest, quia ipsae superficies fieri infinitè laeves nonpossunt. Deinde vis illa quae ad Suctorem revellendum adhibetur, cavitatem Cylindri aliquantulum distendit. Postremo, si in confinio duarum dictarum superficierum ingrediatur una tantum atomus dura, aër purus eâ viâ ingreditur conatu quantumvis debili. . Poteram etiam computasse aërem illum qui propter eandem causam insinuasset se per Cylindri valvulam. Sublatam ergo vides consequentiam à retractione Suctoris ad locum vacuum. Sequuturum hoc quo (que) est, aëremillum qui est in locum à Suctore desertum impulsus, quia magnâ vi impulsus est, motu valde celeri & per circuitum inter summum & imum in Cylindro moveri; cum nondum sit quod motum ejus possit debilitare: Scis autem nihil esse quod sibi motum aut impertiri possit aut diminuere. But this Ratiocination containeth divers things lyable to exceptions; and in order to the examining of it I must premise, That I know not why Mr. Hobbs should here confine his discourse to the Pump without taking notice of the Glass, for whose evacuation 'twas designed. Wherefore for easier considerations sake we will consider, how this discourse will account for the Exhaustion of the Receiver, as well as for the Cylinder; for we usually empty them both in the same tryals. And he being obliged to explicate the Exhaustion of the one as well as the other, it will be convenient to take into consideration the Receiver also, because that being of Glass and transparent, we can better see what happens in it than in the opacous Cylinder. This premised, we may now proceed to the Exceptions themselves. And, first, I do not clearly see by this Explication how he avoids a Vacuum: For, according to his first words, the external [Page] Air is displac'd by the motion of the Sucker outward, and this displac'd Air must move that which is next to it, and that the next, and so onward, (whether in infinitum or no he declares not;) so that at length (tandem) the Air must be compell'd into the place deserted by the Sucker: so that till this returning Air get in betwixt the Sucker and the Cylinder, how appears it from this Discourse, that the deserted space was not empty for some little while? For, certainly, all these motions of the Air forward and backward could not be perform'd in an instant; as may appear by the motion of Sounds and Echo's, whose Velocity is reducible to measure. Secondly, though he takes his Adversaries to be Vacuists, yet (to give an account of these Phaenomena) he supposes the Plenitude of the World; as may appear both by express passages in his Dialogue, and by his here rendring no other probable cause of the Airs getting into the room relinquish'd by the Sucker. But, because I have not here taken upon me the person of a Vacuist, I shall offer some other Considerations. I wish then, thirdly, that Mr. Hobbs had declared from whence the regress of the Airs impulsion should begin; for that may well be required from one that, making the World full, and for ought appears (the Celestial Globes excepted) fluid, allows us to believe it infinite, if the Magistrate shall please to enjoyn us that belief. Fourthly, I demand what necessity there is there should be such a forcible return of the impulse, as is requisite to thrust in the Air at so narrow a passage as that between the Sucker and Cylinder. For, why may not that impulse when diffused in the vast ambient Medium, be so communicated and blended among the differing motions of the other parts of it, as not to return again from whence it begun? As we see that a Voice, though strong, will not move the Air beyond a certain distance smartly enough to be reflected in an Echo to the Speaker: and a stone cast into a Lake will have the Waves it makes diverted from returning to the place they began at. Fifthly, I do not likewise see [Page] that 'tis prov'd, or probable, what Mr. Hobbs affirms of so thick a Cylinder as ours, that it should be distended by the depressing of the Sucker. But this I insist not on; for the main thing that is peculiar in Mr. Hobbs's Explication is, That as much Air as is driven away by the Sucker, gets presently in again betwixt it and the Cylinder: wherefore let us examine that a little. I say then, that by the Air which is so supposed to get in, he either means, in the usual sense and in ours, the Common Air, such as we live and breathe in; or he does not.

If he do speak of such Air, I can plainly prove by several Experiments, that our Engine is in great part devoid of it.

For, first, if there be a contrivance made, whereby the whole Pump may be covered with Water, one may, as we have tryed, plainly see the Air that is drawn out of the Receiver, at each reciprocation of the Sucker, pass in great bubbles out of the Valve through the water.

Next, it appears by the Magdeburg Experiment formerly mentioned, that by reason of the recess of the Air, the Globe of Glass, whence it went out, was diminish'd in weight above an Ounce. Thirdly the same truth may be proved by the Experiments formerly mentioned of the swelling of a Bladder, and the breaking of an Hermetically-seal'd Glass upon the recess of the ambient Air: these Experiments having been already vindicated from Mr. Hobbs's very improbable Explications of them. Fourthly, the same may be prov'd by the breaking of weak or ill-figur'd Receivers inwards; of which in our Hypothesis the reason is clear, but not in Mr Hobbs's. But, fifthly, (not to multiply Instances, though that were easie for me) what I contend for may be sufficiently proved by this one Phaenomenon, That though, if the Receiver being full of common Air the Key be turned under water, the water will not at all be spurted up at the open Orifice: yet the like being done after the Exhaustion of the Receiver, we have had divers Gallons of water violently impell'd into [Page] the cavity of the Glass; which could not happen if it were full of Air, both in regard there can be no probable cause assigned why the water should be thus spurted up; and because the Receiver being already full of Air, either two bodies must be contained in one place, and so we must allow Penetration of Dimensions; or else common Air, to which Glass is impervious, must pass through the water, which we conclude it does not, because no such bubbles are made in the external water as would appear if common Air past through it: Nay, so little of this common Air was sometimes left in the Globe us'd at Magdeburg, that when the water was suffered to rush in, it reduced the Air into less by the beholders estimate than the thousandth part of the capacity of the Globe: And even if our Receiver be unstopt, not under water, but in the open Air, the ambient Air will violently press in with a noise great and lasting enough to argue that the Glass was far from being full of such Air before.

And thus we may argue against Mr. Hobbs, if he would have the Engine, when we call it exhausted, fill'd with common Air, as his words in the recited passage (where he talks of the external Air, and that impell'd into the Cylinder, without differencing them) seem to intimate. But because by some other passages of this Dialogue he may be favourably thought to mean, that the pure Air (as he speaks) is that which gets in by the sides of the Sucker into the Pump, and so into the Receiver; let us consider his Explication in this sense also. And not to urge, that it had not been amiss if, to avoid ambiguity, he had more clearly exprest himself, and named that Other here, as well as he elsewhere calls it so: not to urge this, I say, I desire it may be taken notice of that if Mr. Hobbs take the Air in this Second Notion, he opposes not what I have delivered; the Air I pretend to be pumpt out of the Receiver being the common Air, which consists in great part of grosser Corpuscles than the AEthereal substance; and therefore I might safely pass on to another [Page] subject. But I consider further, that even this explication of Mr. Hobbs's will be lyable to the two first Inconveniences lately objected against the other in favour of the Vacuists; and to divers of those things besides, that are objected in the following parts of that Discourse. Next I observe again, that though the Pump be all the while kept under water, yet the Exhaustion of the Cylinder and Receiver will be made as well as in the open Air: I demand then of Mr. Hobbs, how the pure Air gets in by the sides of the Sucker that is immers'd in water? I presume that for want of a more plausible Answer he will here say, (as he elsewhere does in an almost parallel case) That the Air passes through the body of the water to fill up that deserted space, that must otherwise be void: But then I appeal to any rational man, whether I am obliged to believe so unlikely a thing upon Mr. Hobbs's bare affirmation. If I be, I must almost despair to prove things by Experiments; and if he will allow me to expect from him as much as he seems to do from me, I shall scarce despair to maintain almost any Hypothesis I please: For, besides that he does not so much as pretend by any Phaenomenon to countenance this bold assertion, there are Phaenomena that make against it. For I know not how many Experiments shew us, that when Air passes through Water, it makes bubbles there, which in our case do not appear. And besides, I see not why the outward Air should not rather impell the water (as we see it frequently does in such cases) than be supposed to dive so strangely and unperceivedly through it. When also the diligently-exhausted Receiver is unstopt under water, he that observes how the water rushes in with a stream as big as the passage will give leave, will hardly imagine that at the self-same time as much Air as there gets in water can pass through the same hole without being perceiv'd. But it may by Plenists be said in Mr. Hobbs's behalf, and it seems the most that can be said, that either his Explication or a Vacuum must be admitted. To which I reply, First, that he [Page] has not evinc'd there can be no Vacuum; having endeavoured to prove it but by a single Experiment, which at best does not more strongly plead against a Vacuum than this does for it. Next that we have lately made it probable, that by his Explication he does not avoid the necessity of a Vacuum. And thirdly, that a Plenist without having recourse to Mr. Hobbs's precarious diving of the Air, may more probably decline the necessity of yielding a Vacuum by saying, according to the Principles of the Cartesians, (the subtilest and wariest Champions for a Plenum I have yet met with) that the AEther is by the impulse of the depressed Sucker and the resistance of the ambient Bodies squeez'd in at the pores of the Glass or Cylinder into the cavity of the vessel, as fast as room is there made for it. And I confess, I somewhat wonder at Mr. Hobbs's being averse to this way of salving the objected Difficultie, since (a little above the middle of that passage of his we have so long been examining) he supposes the parts of the Air to be infinitely subtile; which if they are, I know not what pores can be too narrow for them to insinuate themselves into. But, to press this no further, I must here take notice, that whether the cavity of the Receiver be resolved to be (totally or in part) empty or full of Mr. Hobbs's AEtherial Body, or the Cartesians Celestial matter; the violent rushing in of the water, when the vessel is unstopt under that Liquor, and divers other Phaenomena which will not be ascrib'd to the subtile matter within (to which they attribute not any attraction) sufficiently argue that there is in the External Air a far greater power of pressing inwards, than there is within of resisting; and consequently such a Weight or Spring in that Air as my Epistle challenges to it. I had almost forgot to Answer the last lines of Mr. Hobbs's so often mentioned passage, where he would have the Air that he supposes to be impell'd into the Sucker, to move very swiftly betwixt the top and bottom of it. And so elsewhere he would have the same Air, when it gets into the cavity of the [Page] Receiver. But having tired my self, as I fear I have you, by dwelling so long upon one passage; I will skip somewhat that I here approve not in the Ratiocination, and onely say, that when a light Bladder is suspended in the cavity of the Receiver, it betrays no such motion as is here imagined; nay, the flame of a Taper, as our Epistle mentions, was not blown out, nor (for ought appeared) stir'd by this suppos'd wind: to which I shall adde, that Smoke produced in the Receiver whilst it remained exhausted, was not by this vehement motion of the Air blown about the Receiver, as is particularly set down in our Appendix, promised by the Translator of the newly-mentioned Treatise. But if you let in the Common external Air at the Stop-cock, that indeed will rush in with Noise and Violence, and whirle about the Bladder that hung quietly enough before.

Having thus examined Mr. Hobbs's First solemn Explication, I now proceed to the next, wherein he undertakes to give an account by his Hypothesis of the Reason, Why in our Engine, if the Manubrium of the deprest Sucker happens to slip out of the Pumpers hand, the Sucker is carryed up again towards the top of the Cylinder. But since this Explication is such, that though he mentions it as his first, presently after the Recital of his two Hypotheses, he himself is pleas'd to confess in the last page of his Book, that 'tis Erronious; I shall forbear to vex it, thinking such acknowledgments more fit to be imitated whenever there is the like occasion, than to be discouraged. But as for the Explication which at the end of his Dialogues he substitutes for his Retracted one, I confess to me 'tis so obscure, that I know not well what to make of it. But, as far as upon consideration I can understand it, it is coincident with that, which in our Method will be call'd his Fourth Explication; with which that it may the better agree, seems one of the chief Reasons of his altering it from what we had proposed at first. Wherefore we should presently fall upon examining them both together; but that between [Page] them I meet with an Explication (which in our reckoning is the Third) of the Torricellian Experiment.

And here he spends many words to prove the Opinion he had whether proposed or adopted in his Elements of Philosophy; namely, that the place deserted by the suspended Mercury is not empty, but full of Air. But because this Exposition assumes what he has not yet Demonstrated, viz. Non dari Vacuum, and because the Torricellian Experiment as 'tis wont to be made is none of the Phaenomena of our Engine; I shall refer you to what those Learned men Doctor Ward and Moranus have prosessedly, and the first of them largely enough, written against Mr. Hobbs's Explication, (yet without making all that either of them teaches mine:) Because, for my part, it will suffice me to argue, as I did before, that if he takes the Air in the common sense of the Word (and that wherein his Readers generally understand him) his conceipt is manifestly Repugnant to several such Phaenomena as these. That if the Experiment be very well made, we may by inclining the Tube impell the Mercury from its wonted station to the top of the Tube; which will not happen in case the Air were before Inclination let into that deserted space. That if when the Mercury is setled at its wonted station, the Tube be lifted up out of the Restagnant Quicksilver, the outward Air will drive up the heavy Mercurial Cylinder oftentimes with force enough to beat out the sealed end. To which we shall adde onely this Experiment: The Quicksilver resting at its wonted station, if you carefully stop the lower Orifice under the Surface of the Restagnant Quicksilver, and then lifting up the Tube (that which we us'd was about three or four foot long) into the Air, keep it well stopt, if, I say, you first depress one end and then the other, you shall find the Quicksilver fall against the deprest extreme of the Tube with such swiftness and force, as will perhaps surprize you, and make you apprehend that the Tube will be either beaten out of your hand or broken: [Page] Whereas if unstopping the Tube whilst the self-same quantity of Mercury remains in it, you let the outward Air into the cavity unpossest by the Mercury, and then if you again stop the Orifice with your finger, and proceed as formerly, you shall perceive the motion of the included Liquor to be very much slower and less violent than formerly, by reason of the resistance of the admitted Air: which will also manifestly disclose it self by the conflict and bubbles that will be produc'd betwixt the Air and Quicksilver in their hasty passing by one another to the opposite ends of the Tube.

If any friend of Mr. Hobbs's seeing the manifest inconveniences of this opinion, shall on his behalf pretend that 'tis what he calls the pure Air, that passes through the body of the Quicksilver to the deserted part of the Glass Cane; the answer is ready, that Mr. Hobbs's expressions look so much another way, that his Readers (for ought I have found) do generally understand him of such common Air as is displac'd by the descent of the Mercury. And therefore I had reason enough to argue against what he wrote, as I have newly done; and however, this assertion is clearly precarious, and lyable to the Objections formerly alledg'd against the passing of the Air through the water. To which we may adde this circumstance, that in our present case it must descend into a far heavier and closer Liquor than water. But perhaps it will be thought, I have already said more than needed against an opinion which has been rejected as well by Plenists as Vacuists; and though mention'd as to the main by several Writers, as well before Mr. Hobbs asserted it as afterwards, has been thought so unlikely, as not to have been (that I know of) approv'd by any man, even before the discovery of the Phaenomena of our Engine. Which last words I adde, because that Mr. Hobbs not pretending that any attraction intervenes in the case, I see not how he can possibly make out, to omit other Phaenomena, the descent of the Mercury in the Tube further and further beneath its wonted station, [Page] upon the Exhaustion of the Receiver, and the re-ascension of the same Mercury in the same Tube, as we please to let in more or less of the outward Air; without admitting as much of Spring or Pressure in the Air as I need contend to have here allowed me. The weight of the Terrene Particles, by which, at the end of the third Exposition, he is reduc'd to endeavour the Solution of the Quicksilvers falling lower at the top than at the bottom of a Hill, (for I am willing to think that is his meaning, and that 'tis by the Transcribers fault rather than his, that resolutely affirms the quite contrary) will by no means serve his turn: It being utterly improbable to imagine, that the contain'd in so little a vessell as one of our Receivers can by its weight counter-balance so ponderous a Cylinder of Quicksilver: Whence we may be allowed to argue that the Air sustains it by such a Pressure or Spring as we plead for, whether that proceed from the Texture of the Aerial Particles, or from their Motion, or from both.

The Fourth and last of Mr. Hobbs's principal Expositions is of that Experiment of ours, wherein 100. and odde pound weight being hung at the depressed Sucker, the Sucker was notwithstanding impell'd up again by the Air to the top of the Cylinder. Of this Phaenomenon (which has not hitherto prov'd unwellcome to the Vertuous) Mr Hobbs gives us the following account.

Haerent hic nostri: (which why he sayes I know not) quomodo haec expedies tu? Page 22.

A. Expedivi ante. Aër enim à retractione Suctoris retrò pulsus, nec locum in mundo (ut supponimus pleno) quò se recipiat inveniens, nisi quem ipse, corpora contigua suis locis pellens, sibi faceret, perpetuâ pulsione in Cylindrum tandem cogitur, tantâ velocitate inter Cylindri concavam & Suctoris convexam superficiem, quant a respondere solet viribus illis magnis quas ad Suctorem revellendum necessarias expertt estis. Aër autem ille, quâ velocitate ingreditur, eandem ingressus retinet,[Page]simul (que) latera Cylindri aenei (vi elasticâ praediti) undiqua (que) distinet. Conatur ergo Aër in Cylindro vehementer motus contra omnes partes superficiei Cylindri concavae; srustra quidem dum Suctor retrahitur: sed quamprimum Suctor manu emissus Aërem impellere cessat, Aër ille qui ante incussus erat, propter conatum in omne punctum superficiei Cylindri internae & vim Aëris elasticam, insinuabit se inter easdem superficies eâdem velocitate quâ impulsus fuerat, id est, eâ velocitate quae respondet viribus impulsionis. Si ergo tanta ponderis vis Suctori appendatur quanta manuum vis erat quâ impellebatur, velocitas quâ idem Aër è Cylindro exit, locum in mundo pleno nullum habens quò se recipiat, Suctorem rursus ad Cylindri summitatem impellet, propter eandem causam quae effecit ut Suctor paulo ante impulerit Aërem. Thus far our Authors passage: against whose solution 'tis easie to draw divers Arguments from what we have discourst against the first of his four Explications. But though we refer you thither, yet we will here also observe, that this whole conceipt of the Aires running in and out with strange velocity between the Sucker and the Cylinder is precarious; nor does he propose any one Phaenomenon to countenance it. To which general Advertisement I shall adde the three following particulars. First, that in an Engine so contrived, that the Pump lay cover'd with water, when the Sucker was retracted, the Atmosphere would strongly press the water against it; and if the Manubrium were let go, would swiftly enough repell up the Sucker into the deserted cavity of the Cylinder. Which being a case Parallel to that under consideration, let any unbiass'd Person judge how likely it is, that the Air could perform all these Excursions without exciting bubbles, notwithstanding the Waters constant interposition betwixt it and the Cylinder. Secondly, that there is as little probability in what our Author teaches in those words Conatur ergo Aër, &c. I might here repeat what we formerly mention'd of the breaking of our Receivers inwards, not outwards; and [Page] I might adde, that I see no reason why the Conatus of the Included Air, if its Conatus were granted, should be frustraneous, when the Sucker is deprest. But I will rather demand, Why, if the Air within have so strong an endeavour outwards, as to stretch the thick sides of the Bras. Cylinder, as Mr. Hobbs (with what probability, let any man judge) would have it; I demand, I say, why this Air does not throw out the Wooden Peg or Valve, which we have often to our trouble seen thrown out with great force and noise, when the deprest Sucker being thrust up again whiles there was Air in the Cylinder, we forgot to leave the Valve open; though in this case the Air that drove out the Peg was far enough from stretching the Cylinder. And I further demand, how it comes to pass, that, if having stopt the hole of the Cylinder with your finger instead of the Peg, you swiftly depress the Sucker, you shall be so far from feeling a Pressure outwards against the Pulp of the finger from any thing contain'd in the cavity of the Cylinder, that your finger will be strongly, and perhaps not without some pain, prest in by the ambient Air; in so much that 'twas this Phaenomenon, and one somewhat like it in the Torricellian Experiment, that seem to have ingag'd my other Adversary, the Learned Linus, to maintain a conceipt quite contrary to Mr. Hobbs's, and imagine in the deserted cavity of the Cylinder, not a distending, but violently contracting substance. Thirdly. That as to the last part of the passage under consideration, beginning at si ergo, &c. which seems to me somewhat intricate, I do not so clearly understand why the Air that is impell'd in so swiftly betwixt the Cylinder and the Sucker, should not resist the swift Egress Mr. Hobbs ascribes to the included Air by the same passage: nor why this impell'd Air, that has so strong an endeavour outward, should never depress the Sucker (against whose upper part it must bear as well as against the Cylinder) as well as the same Air diffusing its Motion through the vast ambient Medium, can [Page] enable the external Air to thrust up the Sucker again; especially, since during such a depression of the Sucker (as we have mention'd not to happen) made by the Rebound of the Air, forcibly impell'd in from the close bottom of the Cylinder, the Air from without may all the while, with congruity enough to Mr. Hobbs's principles, get in between the said Sucker and the Cylinder. But not to insist upon these niceties: I say, that the lifting up of the Sucker either is not necessary to prevent a Vacuum, or that in some cases it will be hard to shew how a Vacuum can by Mr. Hobbs be avoided. For when the deprest Sucker is ready to be thurst up again, if you hang a somewhat greater weight at it than an hundred and odde pounds, it shall not be lifted up at all. And I shall make this further improvement of the Experiment under consideration, that whereas this progress and regression of the impulse of the external Air cannot reasonably be suppos'd to be very lasting, you may by a competent weight detain the Sucker deprest, till the ambient Air is as quiet as it uses to be; and yet if then you take off the overplus of weight, and perhaps a little more, in case the Pump have been very stanch, the Sucker and the great weight appended will notwithstanding be carried up: which 'tis no way likely it could be by the impulse of the outward Air, which had time to decay and be confounded. And as for the inward Air, beside that we have proved, that it has no such conatus outwards as Mr. Hobbs pretends, why should not that, were it granted, throw out the Sucker rather than cause it to be impell'd inward; it being no way likely, that in case some Air should get out of the cavity of the Cylinder, it could so move the outward Air, as that the reflex of that impulse should make that free outward Air bear more strongly against the outside of the Sucker than the inside of the same Sucker is prest against by the included Air, whose impetus is incomparably less diffused? But not to be thought a more nice and diligent Opponent than the matter requires, I shall [Page] drive this Discourse no further: but rather desire it may be observ'd in general, that whatever be resolv'd to be in the Cavity of the Cylinder when the Sucker is deprest; yet since 'tis manifest, that it is at least in great part devoid of common Air, and since the Sucker with the appended weight may, if the Instrument leak not, be impell'd up, when in all probability those forced Undulations of the Air, that may be supposed to have been made by the Sucker, have ceast; the Cartesians, Mr. Hobbs, and those others that will not have recourse to the un-intelligible attraction of some rarefied substance within, must ascribe so strange a Phaenomenon to the pressure of the Air without. But I shall no further press this Fourth Objection, partly because 'tis added to the other three onely ex abundanti, and partly because this Chapter is grown so long already

I know indeed that after the Exposition last recited out of Mr. Hobbs, he makes the Academian Dialogist confess, that the rest of the Phaenomena of our Engine may also not uneasily be reduc'd to his principles. But perhaps they that take notice of the variety of those Phaenomena we have set down in our Treatise, will scarce be of his mind; and those that have considered what has been discours'd in this Chapter against his four principal Explications, and what I am about to subjoyn in the following part of this Treatise, concerning divers other Solutions that he gives, Will perhaps be inclined to think that others may be like these, without being therefore necessarily true.

CHAP. V. In which divers scattered Explications and other passages in Mr. Hobbs's Dialogue are examined.

I Proceed then to the Fifth Chapter, in which and the next I glean up and examine divers scatter'd passages, wherein he offers at somewhat by way of Argument against some things we had delivered in our Epistolical Treatise: I say, [Page] what he offers by way of Argument; for as to those passages that do but either praise himself or disparage his Adversaries, I have almost as little leisure as inclination to take notice of them, and do not much apprehend that the Virtuosi (especially such as know us both) will think what I write the less rational for being civil; or will let me suffer in their Opinions for neglecting to trouble them in aPhilosophical Controversie, with matters that do but very little belong to it.

To skip then what Mr. Hobbs is pleased to say in the first Page of his Dialogue, concerning some disputable discoveries about Sensation, which he challenges to himself; and to pass by divers other things in the second or third following pages, which relate to him, or to the Society he writes against, rather than to the nature of the Air; we should begin with the Opinion he thinks fit in the fifth page to impute to us, as if we distinguish'd what is fluid from what is not so, onely (for so his Ratiocination imports) by the bigness of the parts of which a Body consists: But designing in an Appendix to be subjoyned to this Discourse to examine what I find in this Dialogue dispersed touching Fluidity, I shall now onely say, that he does very much mistake and mis-represent my Doctrine of Fluidity; wherein I expresly teach, That the principal cause or condition of it is not the size, but the motion of the small parts that compose the fluid body.

To take up then the particulars we are to examine, in the order (as far as conveniently may be) wherein I find them lye in the Authors Dialogue, and passing by at present those things which either we have considered already, or are not to consider in this place; The first particular that offers it self to be taken notice of, is this passage at the bottom of the twelfth page;

B. In vas apertum infudimus aquam, in aqua fistulam Pag. 12. statuimus erectam, longam, exilissimam; observavimus autem aquam è vase subjecto in erectam fistulam ascendisse.

A. Nec mirum; nam superficiem aquae, particulae aëri interspersae[Page]aquae (que) contiguae motu suo verberabant, ita ut aqua non potuit in fistulam non ascendere, & sensibiliter quidem in fistulam valde angustam.

To this I say, that 'tis manifest by what I write in my Epistle, that I did not then take upon me, nor do I undertake in this place, to assign the true reason of the propos'd Phaenomenon. An Attempt of this kind has been since address'd to me, which being ingenious, if not also true, may be consulted. In the mean time I cannot but declare that I am no way satisfied with Mr. Hobbs's Exposition: For, to say nothing of the motion he ascribes to the particles dispersed through the Air, he leaves the difficulty unsolved, since there being common Air as well within the Cavity of the slender Pipes as without it, he neither shews, nor so much as offers at, a reason why the pressure of the Air within should not resist the pressure of the same kind of Air without; as we see it does in greater Pipes. And possibly he would have past by this particular, if he had not overlook'd the Advertisement I gave towards the close of the 35. Experiment, That it would concern those who should undertake to shew the causes of this Phaenomenon to bethink themselves also of a reason why, if the Experiment be tryed with Quicksilver instead of Water, the Surface of the Liquor will instead of being higher, be lower within the Pipe than without it: Whereas if Mr. Hobbs's Explication be sufficient, why should not the contrary happen in Quicksilver as well as in Water?

The next passage I have to consider is in the 13. page thus set down; Siquis post impulsionem revulsionem (que) Suctoris aliquoties repetitam, Epistomium superni Page 13. orificii Recipientis conetur extrahere, inveniet illud valde gravitare, tanquam si multarum librarum pondus ab eo penderet. Vnde contingit hoc?

A. Ab aëris qui est in Recipiente fortissimo conatu circulari facto à violento ingressu aëris inter superficiem Suctoris convexam [Page]& Cylindri concavam, generato per iteratam illam impulsionem revulsionem (que) Suctoris, quam vos perperam vocatis exuctionem aëris. Nam propter naturae plenitudinem, Epistomium extrahi non potest, quin aër qui est in Recipiente (Epistomio contiguus) una extrahendus sit. Qui quidem aer, si quiesceret, facillimè Epistomium sequeretur: sed dum velocissimè circuit, satis difficulter sequitur; id est, videtur esse valde gravis.

B. Verisimile est: Nam ut aër novus in Recipiens paulatim admittitur, etiam apparentem illam gravitatem paulatim perdit.

But, I do not much fear that this Explication will keep the Experiment from continuing to be thought by ingenious men, a notable Confirmation of our Hypothesis. For, to pass by something that, though I am no way satisfied with, cannot well be examined in few words; I answer, First, that if there be such a vehement circular endeavour as he imagines of the Air in the Receiver, by which motion he elsewhere teaches (as we have seen above) that the Air rushes out with violence enough to make the Atmosphere lift up in our Cylinder above an hundred pound weight; I see not why it should not rather throw out the stopple under consideration, than hinder its extraction. And I see not why, when the external Air is re-admitted at the stop-cock into the exhausted Receiver, and thereupon there does sensibly follow for a little while a whirling about of the included Air, the stopple, that just before seemed so much to resist the being drawn out, should cease to make any such resistance. Nor do I see how the plenitude of Nature should, as is here intimated, hinder the extraction of the stopple: For, according to the Plenists, the World and the Receiver must be at all times equally full. And if the contiguous Air must for Mr Hobbs's reason necessarily be extracted with the stopple in one case, I see not why the like should not happen in another. But since Mr. Hobbs is pleased to call us Experimentarian Philosophers, let us shew that such Explications as these of his need not make us asham'd of the name. I say [Page] then, that it appears by our Experiments that there is no such Fortissimus conatus circularis in the exhausted Receiver as he pretends; but that there is indeed an endeavour of the Ambient Atmosphere to press inwards the parts of the Glass and Cover that are contiguous to it. For, as I have also noted already, a light Bladder suspended in the cavity of the Receiver betrayed no such motion as Mr. Hobbs here supposes. To which I shall now adde, that neither were a pair of Scales suspended within the same Cavity; nor was a long Magnetical Needle that rested upon the point of another Needle, at all whirled about by this imaginary motion of the Air. Besides, if you leisurely loosen the Brass stopple, so that it may be very near, but not contiguous, to the sides of the Socket, you shall manifestly perceive a strong current of Air to flow into the Receiver at that passage: And more than once, when instead of that piece of Brass we stopt the hole in the Cover with our Cement, one might observe sometimes whilst we were pumping, sometimes after we had done pumping, that the outward Air by degrees depress'd the superficies of the Cement expos'd to it, and made it concave, and now and then would break through it, thrusting it inward with great violence and noise.

In the same page our Author rectifies, after his way, another of our Explications in these words; Vidimus item aquam demissam in Recipiens post Suctoris aliquot Page 13. reciprocationes ita bullire, ac st supposito igne fervesceret.

A. Id quo (que) accidit propter velocitatem aëris, ut dictum est, in Recipiente circumeuntis; nisi forte aquam illam dum bullit calidam quo (que) esse deprehendatis. Nam si certi essemus illam calescere, alia causa Phaenomeni excogitanda esset.

B. Imo certi sumus quod non calescit sensibiliter.

A. Quid ergo tali aquae motui conferre posse putas majorem vel minorem Atmosphaerae gravitatem?

B. Ne (que) illum motum attribuunt, puto, Atmosphaerae.

But, I confess, I see not how the circular motion of the [Page] Air within the Receiver could in a Vial with a long neck produce such effects as in my Epistle are recited: especially I see not how such a wind passing along the Surface of the Water could raise so many and so strangely-big bubbles, which seemed many of them to rise from the lower parts of the Water, and swell'd notably as they ascended; and how such a wind should carry up the most part of the Water through the long neck of the Vial, and as it were spout into the Receiver.

As for what he sayes about the gravity of the Atmosphere, 'tis plain enough that my conjecture ascribes the Phaenomenon to the taking off, not the gravity of the external Air, but of the pressure of the Air within the Receiver; though I see not why the removal of the weight of the Atmosphere, if it could be out of the Engine effected, should not have a like operation.

And (to answer Mr. Hobbs's Question as it should have been put) that which I think the greater or lesser pressure of the Air confers to this Phaenomenon is this, That whereas common Experience shews us, that water by being heated is expanded, and has bubbles generated in it; and whereas our former Experiments, especially the 28. have made it appear, that there is wont to be in water and other liquors Aerial Particles, which tend to expand themselves, and do actually do so, in numerous bubbles, when the pressure of the incumbent Air is considerably lessened: In the present Phaenomenon that pressure being by the exhaustion of the Receiver taken off, the Aerial particles and agitated Vapours that abound in the hot water are allowed to expand themselves, as before they could not, and to make such numerous and great bubbles, that thereby a good part of the water is carried out of the Vial. So that I somewhat wonder what makes Mr. Hobbs speak as if there were no sensible heat of the water under consideration, since 'tis expresly said that it was put in hot; and if it were put in cold, could by no pumping be brought to the [Page] least shew of Effervescence. And as for his Explication of the Phaenomenon, the Experimentarian Philosophers need not the Objection lately made against it; For I have already evinced by Experiments, that there is in our exhausted Receivers no such peculiar motion of the Air as he ascribes the Phaenomenon to; nay, when there is manifestly a whirling about the Air in the Glass upon the admission of the external Air, the production of numerous bubbles in the water presently ceaseth. And therefore I see not why Mr. Hobbs might not have let alone my Conjecture, (for I propos'd it, and look upon it, as no more) unless he could either have disproved it better, or substituted a more probable one than he has in its place.

As for what he-adds in these words, Ab hoc experimenta manifestum est, quod Recipiens per exuctionem hanc quam vocatis Aeris, non sit vacuum. Nam moveri Page 3. aqua non potuit nisi à movente aliquo moto & contiguo. Ita (que) Phaenomenum hoc demonstrationem suppositionis meae continere videtur non infirmam. I am not obliged to answer it, but leave that to those that are profest Vacuists; against whom I must doubt whether his Ratiocination will conclude, though the consequence be not manifest to me. For himself allows his Terrestrial Atoms an innate circular motion, which consequently needs not depend upon some body contiguous and moved; and the Vacuists will say, that the particles of the water being strongly agitated when it was put into the Receiver, (whether by fiery Corpuscles swarming in it, or otherwise) and the resistance of the incumbent Air being taken off, the Phaenomenon would be produced just as it is, though we should suppose no other body to succeed in the room of the exhausted Air. And besides, though some subtile particles of active matter should get in to agitate the Aqueous and Aerial Corpuscles, yet (they may say) there is no necessity that such minute particles should be numerous enough to fill up exactly all the little spaces deserted by the [Page] Air. And even upon this supposition, as it would not follow that such relinquish'd spaces were all of them quite empty; so would not the Phaenomenon at all prove, much less manifestly prove, that they were quite full. And since an actual heat, that is, a brisk and various Agitation of its small parts, is requisite to the boyling of the water in this Experiment; perhaps others will not think it more absurd, that the removal of the pressure of the Air should occasion this expansive motion in the water, than that which Mr. Hobbs must allow, that in Air comprest by Quicksilver, or some other weight, the removal of that pressure is sufficient to make that Air expand it self by the flying abroad of its parts.

And whereas Mr. Hobbs urges this other Argument against the Vacuists, Praeterea dic mihi, bullientem aquam potuistin' conspicere? Page 13, 14.

B. Quidni?

A. Nonne visionem fieri concedunt vestri per actionem continuam ab objecto ad oculum? Nonne etiam putant actionem esse motum, & omnem motum esse corporis? Quomodo ergo potuit ab objecto, nempe aqua, ad oculos tuos motus per vacuum (id est, per non corpus) derivare?

B. Non affirmant nostri it a vacuum esse Recipiens, ut nullus omnino aër relict us sit.

A. Nil refert an totum Recipiens vacuum sit, an magna ejus pars; nam utrumvis supponatur, derivatio motus ab objecto ad oculum intercipietur.

B. Ita videtur, nec habeo quod respondeam. The Vacuists will perhaps answer him as I answered Franciseus Linus to an almost like Objection. And those of them (which make far the greatest number) who plead but for an interspersed Vacuum, will perhaps tell him, that they take Vision to be made not by such a Propagation of Impulse as he does, but by a Trajection of Effluvia, that issuing out of the Sun, and traversing the Diaphanous bodies interpos'd, rebound from the object to the eye. And according to this Doctrine they [Page] may ask Mr. Hobbs, why a motion may not be made through a Vacuum or non corpus? nay, how it can naturally be stopt in vacuo where there is nothing to resist it? But Controversies of this nature it lyes not upon me to prosecute.

In the 14. page Mr. Hobbs having recited that Experiment of ours, of killing Animals included in our Receiver by the exhaustion of the Air in two or three minutes of an hour, subjoyns these words, Credin'tu animalia istatam cito interempta esse eo quod carerent aëre? Quomodo Page. 14. ergo sub aquam vivunt Urinatores, quorum aliqui (assueti à pueritiâ) caruere aëre per horam integram? Inclusa in Recipiente animalia occidit motus ille idem vehementissimus, quo distenduntur rumpuntur (que) inclusae vesicae. But, though he sayes no more in this place concerning this matter, yet it seems he either much liked his own Conjectures, or greatly disliked mine, since in his Epistle Dedicatory to the learned. Sorberius he singles out this sole Phaenomenon to explicate; Ego contra (sayes he there) ne (que) aërem exugi posse, ne (que) inclusum animal (etsi exuctus esset) tam cito moriturum esse existimo. Actio quidem quam mors illa sequitur videri potest vel suctio quaedam (& propterea exuctione conclusi aëris interfici animal, respiratione sublatâ) vel etim compulsio aëris ab omni parte versus caentrum sphaerae cui animal includitur; & sic videri potest mori à tenacitate compressi aëris, quast aqua suffocatum; nimirum haustum in intima pulmonum aërem solito tenaciorem, inter arteriam & venam pulmonis, cursum sanguinis intercipiendo sistere. But, as I proposed my Coniecture doubtingly, and profess my self to be in a further enquiry about the use of the Air and of Respiration; so I must still think, that we want some further or clearer discovery about that matter, notwithstanding what has been delivered concerning it by Mr. Hobbs. For his Argument against my Conjecture is in the passage that propose, it answer'd by himself: for he plainly intimates that Divers who can live without Air (which [Page] yet I might question, if he means without any Air at all) for a whole hour, are accustomed to it from their Childhood. Wherefore, unless the Animals that dyed in my Engine had been for a long time framed by degrees to live without Air, it will not follow that the want of it could not dispatch them in a short time, as ordinary men may be drowned in a few minutes. And having purposely let down some Mice and small Birds into a deep Glass fill'd with water, and kept them from emerging by a Weight tyed to their legs or tayls, though some lived longer than others, yet I observed them to be kill'd fast enough to keep my Conjecture from being incredible: especially the last we made tryal of, though a large and lusty Mouse, appear'd to be quite dead within somewhat less than one minute, measured by the Vibrations of a Pendulum. And we particularly took notice, that before drowning divers bubbles, which seemed to be the respired Air, came out of their mouths, and ascended through the water.

And as for the Explication that Mr. Hobbs would recommend instead of mine, not to urge that I could wish he had been pleas'd to shew us how the tenacious Air he imagines to be inspired comes to produce those strange Convulsions and other Symptomes mentioned in my Epistle; not to urge this, I say, we have already disproved the supposition his Opinion is built on, namely, that there is in the exhausted Receiver such a motus vehementissimus as he pretends: besides that he shews not how this motion comes to kill the included Animals which I was wont to keep, not near the Centre of the Receiver, where he seems to think this motion most operative, but near the bottom of it, that the included Animal might have something firm under his feet. Nor does it at all clear the difficulty, that he would have this motion the same whereby included Bladders are distended and broken. For, besides that 'tis very hard to conceive how the tenacity of the Air, or its beating from all parts upon the convex Surface of an almost quite empty [Page] Bladder, (for in such also the Experiment he refers to will succeed) should make it burst outwards; besides this (I say) we have already proved that the distension and breaking of Bladders in our Receiver proceeds not from any such motion of the neighbouring Air as is here presumed, but from a quite differing, if not from a contrary cause.

In the same page our Author makes a digression from the Engine, and discourses of another Experiment which I have long since often made: but though his Explication be lyable enough to just Exceptions, (as I can make good if it be required) yet because the Experiment is none of those I delivered, I shall leave it to be examined by others: and for the same reason I forbear to meddle with that he has in the next page concerning the Wind-gun, as to what he has in the same 16. page in these words, Placet mihi tua magis Hypothesis quam illa de vi aëris elastica: nam Page 16. video quod à veritate illius veritas dependet vel vacui vel pleni; sed à veritate hujus nihil sequitur in neutram partem quaestionis. Aëris, inquit, structura similis est compressae lanae. Bene est. Lana fit ex filis. Recte. Sed cujus figurae? Si Parallelopipedi, nulla potestesse compressio partium: si non Parallelopipedi, erunt inter fila illa spatia quaedam relicta; quae si vacua sunt, supponunt Vacuum, ad probandum quod Vacuum est possibile; si plena, plenum dicunt quod vacuum putant. To this passage, I say, I cannot but represent, that the Question is not, whether from the Hypothesis that ascribes a Spring to the Air, depends the proof of a Vacuum or a Plenum, but whether the Hypothesis it self be true or no. For, sure there are many things certain in Natural Philosophy, from whose truth that of a Plenum or a Vacuum cannot be deduc'd. And to what he addes concerning the structure of the Aërial Particles, the Vacuists may tell him, that they make no such Argument as he is pleased to make for them; and do not commonly imploy the Figure of the Aërial Particles to prove a Vacuum, but other Arguments, such as Mr. Hobbs has not yet well [Page] answered: and having by them, as they judge, prov'd interspersed Vacuities, they might without inconvenience suppose in an Aërial Corpuscle little empty Pores, upon whose account it may be capable of compression, in case they should think fit (which I know not that any of them does) to assign it the Figure of a Parallelopipedon. But this Controversie the Vacuists may, if they please, prosecute. In the same page Mr. Hobbs begins, and in the next he continues, a long discourse concerning the going out of fire in our Receiver upon the exhaustion of the Air: the passage is too prolix, and does too little concern the Spring of the Air to be here totally transcribed, or examined Period by Period. In summe, he indeavours to do two things: the one is to reduce what happens to kindled Coals placed in our Engine to what happens in certain Mines, wherein when some thick damps ascend, both Charcoals and Candles are soon extinguished thereby: the other is to shew, that by the Reciprocation of the Sucker, the Air impell'd first into the Cylinder, and then into the Receiver, is put into such a motion as gives it a certain middle consistence, as he speaks, betwixt the consistence of pure Air and that of Water. But I shall not need to examine this second part of his discourse, because I deny the first; and being able to disprove the thing it self, namely, the thickness of the Air in the exhausted Receiver, I need not spend time about what he teaches de modo.

To examine then onely the first of the above mentioned particulars, I shall begin with observing that his story of the damp to be met with in Mines is more largely set down by Mr. Hobbs in that Chapter of his Elements of Philosophy, where he treats of Gravity; in which place he seems to mention it (to use his own Expression) as a story of doubtfull credit, which 'tis not like he would have done if had then seen it. Which I mention, not that I deny the story for the main, nor that I would bring Mr. Hobbs into a suspicion of relating things untrue as matters of fact, his enemies themselves [Page] having not accused him of such a meanness; but because, if he have not since observed the thing himself, there may easily be a mistake in some of the circumstances: as for instance, the number of Minutes wherein the thick Air choaks the fire; and 'tis upon that circumstance that the validity of what he deduces from the observation chiefly depends. But, however the matter fare with these subterraneal Damps, we have already proved by several of the Experiments of our Engine, that in the exhausted Receiver there is no such motion of the Air as is here supposed. And it may be sufficiently proved, that whatever remains in the Receiver is not such a substance as Mr. Hobbs would have it: for that, he here tells us, is of a consistence betwixt Air and Water; and in the above cited place of his Elements he sayes, that 'tis not much lighter than Water. But by the Magdeburgick Experiment (we have already had occasion to mention two or three times) 'tis evident that the Receiver by being exhausted of common Air is so far from growing heavier, much less so much heavier as it must if it were filled with a substance not much lighter than Water, that it lost above an Ounce of its former weight. And to this agrees what we see happen in AEolipiles, that grow lighter when the Air is expell'd. Besides, if the Receiver be in our present case filled with a substance whose consistence is so much nearer that of Water than is our common Air, as Mr. Hobbs would have it; how chance a Pendulum should not move very sensibly slower in it, when in Water the Diadromes are so exceedingly much more slow? And the breaking of an Hermetically-seal'd bubble in our Receiver outwards, when the Air was much exhausted, and not before, together with divers other Experiments that might be easily applyed to this purpose, in our Epistle, do sufficiently evince, that 'tis not a thicker and far heavier Air, but a more yielding and lighter, that remains after Pumping in the Cavity of our Receiver. And thus much as to Mr. Hobbs's discourse upon our Experiment. But [Page] as for the thing it self, it appears that when I related it I thought it might admit a further enquiry: And indeed there may be so many ways of extinguishing Fire (as we see that the flame of a Candle may be blown out by the wind, or quenched in water, or put out by the compression of a pair of Snuffers, or suffocated for want of Air to receive its fuliginous steams, or (if that be a different way) stifled by the thick Exhalations of deep Mines or of new Wine) that as 'tis not in all cases so easie to assign the true cause of the extinction of fire, so 'tis unsafe to conclude with Mr. Hobbs, that because a Candle or a live Coal may a great way under ground be extinguisht by a thick Damp, therefore the effect must proceed from the like cause in our Receiver, where there is no sign of any Damp or unusual thickness of the Air, but of the contrary.

But let us follow Mr. Hobbs to the next passage, wherein he seems fond enough of playing the Censor. For, speaking of our 11. Experiment, wherein the Coals that seemed almost dead in our exhausted Receiver, being taken out into the Air began to shine again, having made his Academian Dialogist say, Fuere eorum aliqui qui remansisse dixerunt in carbonibus illis (quanquam extincti videbantur) particulas quasdam igneas, quae admisso aëre ventilate caeteram Page 18. molem denuo accenderent: The other (by whom Mr. Hobbs is meant) answers him, Nae illi quae dicerent non videntur cogitasse, sed sortitos esse. This is very severe. But let us see what weighty reason he has to be so: Credin' tu in carbone ignito partem aliquam non carbonem, sed ignem Page 18. esse; aut in candente ferro partem inesse quod ferrum non sit sed ignis? But some will think that by these words he does rather propose than prove his Opinion: wherefore let us hear his Ratiocination, which he annexes in the following words, Ab unica scintilla magnae urbis incendium nasci potest. Atqui si ignis corpus ab ignito diversum sit, Page 1 [...]. non plures potuere esse partes igneae in toto incendio quam in una [Page]illa scintillula. Videmus corpora diversorum generum à luce Solis tam per refractionem quam reflexionem factam in speculis comburentibus accendi posse: ne (que) tamen quenquam esse credo qui putet particul is igneas à Sole eject as transire posse per substantiam globuli crystallini. In aëre intermedio ignis nullus est. But I doubt his Adversaries will say, that he is so far from having in this passage well confuted their Opinions, that he seems not to have well understood them: For they will tell him, that they teach not that the fire is materially different from every part of the fewel; but that the igneous Corpuscles, whilst they are divided, blended and opprest with the others, have not the power to shine or burn, till being by some spark or other body actually burning, or by some other equivalent cause extricated, they flock together in swarms, and then are able to burn and shine, that is, to appear fire: Which fire is yet but a part of the fewel; as appears by the Phlegme, Ashes, and perhaps other incombustible parts of the Coal or other fewel. So that the Atomists and divers others will not allow what Mr. Hobbs infers about an incendium. And whereas he tells us he believes that no body thinks, Particulas igneas à Sole eject as transire posse per substantiam globuli crystallini; he seems to me to have very little heeded the Epicurean Hypothesis. For, not onely the learned Gassendus, but I know not how many other Atomists (besides other Naturalists) Ancient and Modern, expresly teach the Sun-beams to consist of fiery Corpuscles, trajected through the Air, and capable of passing through Glass; whereby these Authors give an account of those specula ustoria that burn by reflexion. These things I represent, not that I intend here to adopt the Atomists Opinion of the nature of Fire, of which I am not obliged to declare my thoughts here, and have done it elsewhere; but to shew that Mr. Hobbs's Arguments are not a sufficient ground for so heavy a Censure. And if a Coal be kindled at one end, though Mr. Hobbs would have the kindled end a Coal, not Fire; yet if he [Page] please to hold it in his naked hand, he may find that differs enough from the other end to deserve another name. And I, that but related a Phaenomenon, did not perhaps express my self much less warily, if not more so, than Mr. Hobbs himself. For whereas my words are these, We presently took out the Coals, in which it seems there had remained some little Parcels of fire, rather covered than totally Page 79. quench'd: for in the open air the Coals began to be rekindled in several places: Mr. Hobbs even in his Elements of Philosophy speaks thus upon a somewhat-like occasion, If a Grate filled with Coals throughly kindled, and burning never so brightly, be let down, as soon as ever it is below Chap. 30. Sect. 14. C. the fire will begin to grow pale, and shortly after (loosing its light) be extinguisht, no otherwise than if it were quencht in water: but if the Grate be drawn up again presently, while the Coals are still very hot, the fire will by little and little be kindled again, and shine as before.

As for the reason Mr. Hobbs assigns of our Experiment in the lately mentioned passage of his Dialogue, being grounded upon such a thickness of the Air in the Page 18. Receiver as we have already disproved, it needs not to be examined. And lastly, as to what he subjoynes in these words, Quando autem est quod de homine vere pronunciare possumus quod est mortuus, sive (quod idem Page. 18. est) animam expiravit. Cognitum enim est homines nonnullos pro mortuis habitos, postridie elatos revixisse.

A. De puncto temporis quo anima à corpore separatur difficile est statuere. Perge igitur ad experimenta alia.

I confess I see not why that needless Question might not have been well spared, if he designed to give it no better Answer.

[Page]

CHAP. VI. Wherein other passages of Mr. Hobbs's Dialogue that concern the Author are examin'd

WHat our Author has in the 19. page concerning a Bladder has been already examined, wherefore I proceed to the next passage in the same page, which is this; B. Si acus magnete excitus libere pendeat intra Recipiens, sequetur tamen ille motum ferri quod circumducitur extra Recipiens. Item object a intus posita ab iis qui extra sunt videbuntur, & soni intus facti audientur, omnia haec aeque post at (que) ante exuctionem aëris, nisi quod soni sunt aliquanto post quam ante debiliores.

A. Manifestissima haec sunt signa Recipientis semper pleni, nec posse inde exugi aërem. Quod autem soni inde sentiantur debiliores, signum est consistentiae aëris. Consistentia autem aëris à motu ejus est per lineas diametraliter oppositas. But I meet with few of the Vacuists, who, even in the Torricellian Experiment, think the place relinquished by the Quicksilver to be perfectly void, most of them allowing, that though it be not quite full of body, yet it may contain some of the Earth's magnetical steams, or of those igneous Corpuscles that flow from the Sun, or both of them. Now against these who would from our Experiments deduce but onely an interspersed Vacuum, I see not that the Phaenomena mentioned by Mr. Hobbs do conclude half so manifestly as he pretends: For, as to the motion of the Needle within the Receiver, 'tis known that they are wont to ascribe Magnetical Attraction to certain Effluvia, that issuing out of the Loadstone are subtile enough to pass through the Pores of the closest bodies without excepting Glass; so that although the Receiver were quite empty'd before, the Needle might be wrought upon by Magnetical Corpuscles, that need not be supposed to fill the 10th. part of the Receiver. I know indeed that Mr. Hobbs has another Hypothesis of the Phaenomena [Page] of the Loadstone, but I know that divers learned Writers have absolutely rejected it, and not one such that I have heard of has approved it. And as for the other two Phaenomena here mentioned by Mr. Hobbs, the Atomists may answer, That the first (touching Objects seen in the Receiver) has been shewn already not to overthrow their Doctrine: and that the other (concerning the Debilitation of Sounds) makes against him, not for him; since we have already disproved that consistence of the Air whereto he ascribes it. And the same Arguments that overthrow that Opinion may make it seem somewhat strange, that he should subjoyn our Experiment of two like Pendula, whose Vibrations we found not manifestly to differ within and without our exhausted Receiver. For the former should move far slower than the other according to Mr. Hobbs's Conceit, that the Receiver, when we say 'tis exhausted, is filled with a substance of a middle consistence betwixt Compare that in the 30. Chap. 14. Sect. of his Physicks with that of his Dialogue, page 15, 16. pure Air and Water, and not much lighter than Water. But whether the Receiver be in such cases adequately full or no, the Vacuists may further consider. For its being granted to be full would not overthrow either of my Hypotheses, namely, the Weight and Spring of the Air.

In the same 19. and some following pages Mr. Hobbs, has a long Discourse against my Conjecture at the reason I propose in my 31. Experiment, why (as I there express it) if the exquisitely polisht Surfaces of two flat pieces of Marble be so congruous to each other, that upon their mutual application there results an immediate contact, they will stick so fast together, that he that lifts up the uppermost shall, if the undermost be not exceeding heavy, lift up that too, and sustain it aloft in the free Air. The Conjecture it self is in the same page thus set down, That the lower superficies of that (undermost) stone being freely exposed to the Air, is prest Page 6. upon by it; whereas the uppermost surface being contiguous to [Page]the superiour stone, is thereby defended from the pressure of the Air, which consequently pressing the lower stone against the upper hinders it from falling, as we have elsewhere more fully declared. Which last words I therefore omit not, because they shew that I handle this matter in this place but incidentally, and may make use of what I have deliver'd where I treat of it more expresly; as I have since done in Print in the History of Fluidity and Firmness, which Mr. Hobbs appears to have seen by those censures of some passages of it that I shall hereafter examine.

His whole Discourse concerning my Conjecture, and his Scheme, would be too prolix to be entirely inserted. But the thing his Discourse drives at is to shew, that neither the Spring nor Weight of the Air have any thing to do with this Phaenomenon: and therefore when he had made his Academian relate, that two coherent Marbles suspended in our Receiver did not fall asunder upon the exhaustion of it, he subjoyns that it was, Quia nihil istic erat quod ageret Atmosphaerae pondus; and annexes, Experimento hoc excogitari contra opinionem eorum qui Vacuum asserunt aliud argumentum Page 10. fortius aut evidentius non potuit. Nam si duorum cohaerentium alterutrum secundum eam viam in qua jacent ipsae contiguae superficies propulsum esset, facile separarentur, aëre proximo in locum relictum successivè semper influente; sed illa ita divellere, ut simul totum amitterent contactum, impossibile est, mundo pleno. Oporteret enim aut motum fieri ab uno termino ad alium in instante, aut duo corpora eodem tempore in eodem esse loco: quorum utrumvis dicere est absurdum. But how this should be so cogent and manifest an Argument against the Vacuists I confess I do not well discern. For that which it proves (if it prove any thing) seems to be, That in case the cohering Marbles could be so severed as to lose at once their whole contact, the world might be concluded not to be full: But I see not how it thence follows, that therefore there can be no Vacuum. For my part I would demand, whether the so [Page] strong cohesion of the Marbles be necessary or not to the plenitude of the world. If it be, how chance a sufficient weight hung to the lower Marble can immediatley draw them asunder? and if it be not, why does not Mr. Hobbs assign some other cause of their so strong adhesion, if it depend neither upon the Spring nor Weight of the Air? As for the non-separation of the two Marbles in our Receiver, I have said in the same 31. Experiment, that the cause may probably be the pressure of the Air remaining in the Receiver not sufficiently exhausted. And this Conjecture I have more fully defended in what I have written about it against Franciscus Linus, where I shew, that 'tis no way unlikely the remaining Air should be able to sustain a weight of four or five Ounces hanging at the lower Marble, since the free Air was able to support between 400. and 500. Ounces hanging at the same.

But Mr. Hobbs tells us, that the cause I assign of the cohesion of our Marbles is lyable to huge inconveniences; of the greatness of which we may judge by the first of them Confitentur (sayes he) tum ipsi tum alii omnes, ponderationem omnem conatum esse per lineas rectas undiqua (que) ad Page. 20. centrum terrae; & proinde non Cylindrum vel Columnam fieri, sed per Pyramidem, cujus vertex est centrum terrae, basis pars superficiei Atmosphaerae. As if it were much material whether a body whose Basis is scarce two Inches Diameter, and whose length amounts to some thousands of Miles, be considered as a Cylinder or a Piramid. Certainly Stevinus and other learned Writers of the Hydrostaticks would scarce have made this an Objection, since they scruple not to make it a postulatum, that all not very distant Perpendiculars be looked upon as parallel, though they allow such Perpendiculars would meet in the Centre of the Earth. What he adds partly in these words, Conatus ergo punctorum omnium ponderantium propagabitur ad superficiem Marmoris superioris Page 20. antequam possit propagari ulterius (puta) ad terram, and partly in the following lines, to prove that the whole endeavour of [Page] the Pyramid that leans upon the upper Marble is terminated there, and that there is no endeavour of the Atmosphere against the under-superficies of the lowermost Marble; This Ratiocination seems grounded, partly upon a Conceit of his about the nature of Gravity, according to which I see not why any Body plac'd between the sides of that Pyramid or rather Cone, whereof the upper-superficies of the higher Marble is the Basis, should descend upon the account of gravity; and partly from a mistake of my Opinion: for I do no where, that I know of, speak as if I thought this sustentation of the lower Marble were performed by little Globules or other minute bodies protruding one another directly towards the Centre of the Earth, and rebounding from a perfectly smooth superficies; nor need I say, that the lower stone is sustained by the pressure of the self-same pillar of the Atmosphere that is incumbent on the upper, since other parts of the Atmosphere, some on the one hand and some on the other, pressing obliquely upon the uneven surface of the Earth, may have their pressure upward terminated against the lower surface of the undermost Marble. And in the mentioned History of Fluidity and Firmness, speaking (pag. 187.) of the adhesion of flat Glasses, (and the reason is the same in our flat Marbles) I plainly deduce it from the pressure of the fluid Air, which, like a liquor, diffusing it self upon the surface of the Terrestrial Globe, because its descent is there resisted, does, like water and other liquors, press almost equally every way, and strongly endeavour to thrust away any body against which it can bear; so that whereever the pressure is taken off from one part of a body and not from the opposite, that body will be prest toward that part, whether it be downwards, or sidewards, or upwards, where that formerly-equal resistance is removed. And this Explication I do in that Discourse back with Considerations and Experiments, which Mr. Hobbs is not pleased to take any notice of; wherefore I hold it not amiss to adde here two or three other experiments to one of those mentioned there.

[Page]First then, an AEolipile being by heat freed from Air as much as you can, if the little hole at the extremity of the neck, by which the Air gets in and out, be presently and carefully stopt with Wax, and afterwards suffer'd to cool, there will not be in the Cavity of the AEolipile a resistance any thing near equal to the pressure of the outward Air. And therefore if you perforate the Wax, that Air will violently be impell'd in at the unstopt Orifice, whether the neck be held parallel or perpendicular to the Horizon, or in any other situation in respect of the Centre of the Earth. And the like will happen if the AEolipile be unstopt under water.

Next, I relate in the mentioned History, that having drawn some of the Air out of a large Glass with a narrow mouth, and thereby destroyed the equality of force betwixt the weight of the outward Air, and the now weakned spring of the inward; I found that by immediately applying a flat body to the Orifice of the Vessel, that body was readily lifted up and sustain'd in the Air as long as I pleas'd, though the weight of it exceeded 20. Ounces.

Thirdly, I lately met with the relation of an Experiment which does abundantly make out the power of the ambient Atmosphere to press bodies against each other, when it cannot get between their internal surfaces. For the ingenious Author of the Magdeburgick Experiment writes to the industrious Schottus, that having caused two Copper Plates to be made almost in the form of Scales a little above half an Ell in Diameter, and exactly congruous if laid upon one another; Has (sayes our Jesuite) si mutuo sibi imponit, & aërem extrahit, adeo ab externi aëris gravitate Schot. Mech. Hyd. Pneumat. pag. 461.compressae at (que) unitae tenentur, ut sex viri robusti eas divellere non possint. Quod si tandem adhibito omni conatu divellantur, crepitum edunt sclopeti aut Musquetae explosioni non minorem; quamprimum vero per claviculum feu Epistomium apertum vel minimus aditus laxatur aëri, sponte separantur.

[Page]And, Fourthly, if a Glass Vial (such as will be anon more fully describ'd) have a Pipe open at both ends so fitted into it, that no Air can get in or out betwixt the neck and it; and if the Vial be so far filled with water, that the lower end of the Pipe be well immersed therein; if then you suck at the upper end of the Pipe, the water will ascend to a good height; which argues its being forc'd upwards by the oblique pressure of the Air in the Vial; for 'tis onely in the Pipe and not in the Vial that there is any Air in the same Perpendicular with the Water that is impell'd up.

But let us follow Mr. Hobbs a little further. Having ask'd this Question, Sed vis illa elastica quam in aëre esse dicunt, nihilne ad marmor sustinendum conferre potest? he answers, Nihil omnino; non enim conatus in aëre est Pag. 20, 21.ullus ad centrum terrae magis quam ad aliud quodvis punctum Universi. Quoniam enim gravia omnia tendunt à circumferentia Atmosphaerae ad centrum terrae, & inde rursus ad circumferentiam Atmosphaerae per easdem lineas reflexas, conatus sursum conatui deorsum aequalis erit, & proinde mutuo se perimentes neutrâ conabuntur viâ. But that the Spring of the Air may perform somewhat in the case proposed, I hope the newly-mention'd Experiments have evinc'd. And the reason he annexes to his Negative, as also the difficult Example he subjoyns, of a man lying in the bottom of the Sea, seem rather oppos'd to the Weight than the Spring of the Air. But we have already both by Experiments and by his own Concessions sufficiently prov'd that the Air is not devoid of gravity; and that it likewise gravitates upon the terraqueous Globe, which in this page he seems to deny, we have proved by divers reasons, and particularly in our 25. Experiment by the vast expansion of Air under Water, when the pressure of the incumbent Air was taken off from the Water.

As for the Scheme he annexes, I confess I do not well see what he drives at in it; at least if it be intended for a Confutation of the Conjecture I have been defending: nor am I the [Page] onely person that complain of his writing often enough obscurely. And as far as we can judge by the conclusion couch'd in these words Non potest ergo pars, BC. (which in the Explication of the Scheme he calls, Pars Atmosphaerae intra totam posita ubicun (que)) (propter magnitudinem) quantumvis gravis sit descendere, ne (que) ergo premere sive gravitare; his Notions about Gravity are somewhat strange, and probably either do not concern us, or will be found repugnant to those Experiments on which our Conjecture is grounded.

And as for what he adds, Si possibile esse negarem, ut diligentiâ & arte humanâ duae superficies corporum Page 22. duorum inter se per omnia puncta ita accurate congruae fiant, ut ne minimo quidem corpusculo creabili transitus permittatur, non video quomodo illi aut suam Hypothesim tueri, aut negationem nostram improbitatis arguere jure possent: I confess I do not see how this Argumentation proves any thing against the Interest, either of the Weight, or so much as of the Spring of the Air in the cohesion of our Marbles. For, provided that the Corpuscles of the Air get not in between the two stones, the pressure of the Air may well suffice to keep them together. And, lastly, as for that modest passage (that immediately precedes the words newly recited) wherein he sayes, Vtra (que) illa phantasia, tum gravitatis Atmosphaerae, tum vis Elasticae sive Antitupiae aëris, Page 21, 22. somnium erat. Siquidem autem illis concederetur esse aliquam in filiculis aëris Antitupiam, quaeret (que) aliquis, unde illa curvata quidem sed quiescentia moverentur rursus ad rectitudinem, deberent illi, si Physici haberi volunt, causam ejus aliquam possibilem assignare: We have already given an account why we forbore to assign a cause of the motion of Restitution; but methinks Mr. Hobbs might have, for the speaking so, chosen a fitter place than this, where he gives me so far an opportunity to tell him again, that he should, if he would be thought a Naturalist, have assigned some cause of the Phaenomenon about which he had all this while been desputing: [Page] which since even he himself has declin'd to do, perhaps the Phaenomenon will be thought somewhat difficult, and my attempt at discovering the cause of it will be at least excused.

But after having so long dwelt upon the consideration of our Marbles, it is high time to proceed to what remains.

In the 24. page Mr. Hobbs has that passage I formerly recited touching the Glass-Fountains, out of which water is thrown up by compress'd Air. But though I as well as others have made use of such Fountains, invented by Vincenzo Vincenti of Urbin, and was unsatisfied with the account he gives of their Phaenomena; yet in regatd some learned men, and particularly Dr. Ward, have already examined his Explication, and I am not obliged to do so; I shall onely take notice of what our Author objects to prove that this Phaenomenon cannot be solv'd by the Spring of the Air, in these words:

B. Cur non potest aqua, quae cum injiceretur particulas aëris comprimebat, ab iisdem particulis se explicantibus Page 24. rursus rejici?

A. Quia locum explicatae majorem non requirunt quam compressae. Quemadmodum in vase aqua pleno, in qua esset multitudo anguillarum, anguillas sive in se volutas sive explicatas idem semper capit locum. Propellere ergo aquam per vim Elasticam, quae alia non est quam motus corporum se explicantium, non possunt.

B. Comparatio illa aëris cum aqua anguillis plena, nostris, credo, non displicebit.

But the Elaterists will answer, that neither can his earthly Atoms, to whom he ascribes the Rejection of the water forc'd in, truly fill up more parts of space at one time than at another; and therefore the Objection might have been spared: but indeed it reaches us not. For we, as Mr. Hobbs knows well, are not wont to compare the Air to Eels, but to Wooll: and though each hair that makes up a compress'd lock of wooll, do not really fill more space with wooll when extended than when crumpl'd; yet when there is a congeries of these hairs [Page] compress'd together, the whole fleece or congeries does by its spring endeavour to thrust away those contiguous bodies by which it is penn'd up, as I have more fully explained in my Epistle; so that these Aerial Corpuscles, being pent up by the water forc'd into the Glas, still endeavour to expand themselves by throwing it out.

What our Author addes in the same page, as if they were mistaken that think the Experiments of the Plenists tended (especially till of late) to prove that the generality of them did not always mean by a Vacuum a space perfectly devoid of all corporeal substance, but any space here below that is not fill'd with a visible body, or at least with Air, (for these are my words to which I suppose Mr. Hobbs alludes) To this, I say, it is scarce worth while to make answer, the Controversie being of such small moment, (though I think I could easily enough do it) especially since he rather excuses those that may have negligently exprest themselves, than disproves what I said. And since I spoke chiefly and by name of the Peripatetick Schools, he may well allow that their Expressions concerning this matter were not alwayes so accurate, whilst in this very passage he concludes with these words, Vides quam ineptum sit ad explicationem effectuum talium advocare verba Metaphorica, ut fugam vacui, horrorem naturae, &c. Page 25. quibus olim ad existimationem suam tuendam usae sunt Scholae. Nor is what he adds concerning the Vacuum to be attributed to Democritus and Epicurus either clear enough, or of concernment enough to our Dispute, to be insisted on by us; especially since I see not to what purpose he brings it in.

But there are in this page two particulars, which, though they make little or nothing against what I said of the Plenists, may deserve to be taken notice of.

The second (for I think it expedient to dispatch that first) is couch'd in these words, In Hydriis perforatis ideo haeret aqua, quia quae per tantillum foramen exiturit, adeo exigua est,Page 25.ut non posset ita in longitudinem se diffundere,[Page]ut descendendo aditum aëri faciat per foraminum circumferentias; ne (que) aër ab exeunte aqua pulsus locum alium (in mundo pleno) habere potest praeterquam quem aqua deseret.

But this Experiment I have already examined as 'tis propos'd in his Elements of Philosophy; and therefore I shall now onely say to the light variation I find of it here, that the reason here assign'd why the water in Gardeners pots clos'd at the top does not descend, is not rightly assign'd, since (to omit other objections) by Monsieur Paschall's Experiment it appears, that though in Pipes of no great length the water will not run out, yet if the Pipe be long enough, though the Orifice be no wider, the water will descend without giving passage to the Air at the circumference of it.

But the other particular here mentioned by Mr. Hobbs, who thus proposes it, Qui per fistulam ore aquam sugit, aerem medium prius sugit, quo distentum aerem externum removet; qui remotus locum (in pleno) habere nisi Page 25. proximum removendo non potest, & sic continua pulsione aqua tandem pellitur in fistulam, succedit (que) aeri qui exugitur; deserves a more particular consideration. For this account of the ascension of Liquors by suction is not onely here given by Mr. Hobbs, but for the main by the learned Gassendus himself, and other Atomists, and is generally acquiesc'd in by the modern Philosophers; perhaps the rather, because it seems not to establish or overthrow a Vacuum. But though I shall not deny but that many Phaenomena of Nature may be probably explicated by this Propagation and return of Motion; yet there are some Phaenomena here below, which I see not how the Cartesians, or the Atomists, or Mr. Hobbs can explicate without admitting the Spring of the Air, and which perhaps by the Spring of the Air may be explicated without the recurring to such a propagation and return of impulse. Divers instances to this purpose I elsewhere consider, but at present I shall propose onely one Experiment purposely devis'd to [Page] shew that both Vacuists and Plenists should admit an Elastical power in the Air. I took then a Glass-Vessel consisting of two parts; the one was a Vial capable of containing about a pound of water, and the other a Pipe open at both ends, the lower of which reach'd within two Inches of the bottom of the Vial: this Pipe was by the Glass-man fastned into the neck of the Vial, not by any Cement, lest, it should be pretended that the Air might undiscernedly get in or out, but with melted Glass of a good thickness: into this Vessel by the open Pipe I at length (for it is somewhat difficult) pour'd water enough to swim a pretty way above the lower extreme of the pipe, and then often inclin'd the Vessel, to give a free intercourse betwixt the Air within the Vial and that without it, that if the internal Air were comprest by the affusion of the water it might free it self, as it readily did by ascending in bubbles along the inclined Pipe, till the outward and inward Air were reduc'd to an equality of pressure. Now if all Suction were produc'd by the pressure of the Air, thrust away by the dilated Chest of him that sucks, and so thrusting the water or other liquor into the Pipe at which he sucks, it seems evident, in our case, that the water would not ascend by suction: since by the contrivance of the Vessel, the Air thrust away by him that sucks cannot at all come to bear or press upon the water. And yet, whether the Pipe were inclin'd or erected, the water did according to my expectation easily enough ascend, upon suction, to the top of the Pipe, and ran over into my mouth. I say, easily enough, because that though the Spring of the Air pent up in the Vial were able, upon the decrease of the pressure of the outward Air, occasion'd by my sucking, to impell the water strongly enough into the Pipe; yet, when a pretty quantity of water had been so impell'd up, the included Air gaining thereby more room to expand it self, its spring was thereby so far weakned, that the water ascended far less easily than in ordinary suction. The other circumstances worth noting in [Page] this Experiment belong not to this place; and what has been delivered may, I hope, suffice for the purpose 'tis alledg'd for. Onely one particular I shall here adde, by way of confirmation of what I said touching the weakn'd Spring of the Air, and it is this; That partly to shew some, who yet embrace the Opinion of the Schools, that the ascension of the water in the Pipe did not proceed from any such tendency in the water it self to ascend for prevention of a Vacuum, and partly for other reasons that concern not this place, I did carefully take out the water by degrees, till the lower end of the Pipe was but very little under the surface of the water, though in the cavity of the Pipe the water, as it usually will be in Pipes that are not wide, was a pretty deal higher: then suffering the Vessel to rest, and sucking at the upper end of the Pipe, the water (as I foresaw it would be) was impell'd up, yet without reaching near the top, till the surface of it was fallen a little below the bottom of the Pipe. But then, though I continu'd sucking, no more water ascended into the Pipe, but the Air passing through it towards my mouth, did in its passage toss up the water that was already in the Pipe, and turn it into bubbles, (of a strong bigness when the cavity of the Pipe would permit it) which broke (not without noise) one after another: and thus the ascending Air for a pretty while kept the water in the Pipe from falling back to that in the Vial. But when I remov'd my mouth, the Spring of the Air remaining in the Cavity of the Vial, being debilitated by the recess of the Air I had (as men are wont to speak) suck'd out, it was not able to resist the pressure of the outward Air, and accordingly the water in the Pipe was not onely depress'd into the Vial, but the outward Air forc'd its way in many bubbles, and not without some noise, through the water contiguous to the bottom of the Pipe, till the pressure of the included Air and that of the Atmosphere were reduc'd to an equality.

But in the same 25. page our Author tells us, that the [Page] Society he writes against would have the cause of Filtration, and that of the passage of water through Siphons, to be the same. To which he annexes, this peremptory passage, Id vero impossibile est. Nam in Siphone nisi ambo crura aquâ impleantur, aqua è pelvi non ascendet. Ascensionis causa in pannum est motus ille terrearum atomorum quae aquae contiguae sunt, motus (inquam) circularis simplex, aëri in quo moventur communicatus; quae atomi aquam ferientes in materiam laneam incutiunt, incussae autem magis magis (que) madefaciunt, donec madida tota sit. Cum vero madida tota sit, &c. Thus far he; but the passage in my Epistle, upon which he seems to have grounded his Opposition, is but this (wherewith I begin my 35. Experiment) Some learned Mathematicians (I meant the industrious Schottus and some Cartesians) have of late ingeniously endeavoured to reduce Filtres to Siphons; but still the cause of the ascension of water and other liquor both in Siphons and in Filtration needing (for ought we have yet found) a clearer discovery and explication, we were desirous to try, &c. So that neither did I ascribe this reduction (of Filtres to Siphons) to a Society which was not then in being, nor perhaps so much as design'd; nor did I adopt it my self; but express'd a desire to have it further examin'd. But as for the cause of Filtration it self, I may take a fitter opportunity to discourse of it; in the mean time I doubt whether the reason here assign'd by Mr. Hobbs will not seem as well precarious, as the motus circularis simplex of earthly Atoms, whereon it is grounded. Nor does his Explication render a reason why Quicksilver will not ascend the 14. part as high in the Filtre, though in part immers'd into it, as water, nay, will not reach so high where 'tis contiguous to the Filtre, as where 'tis not: nor why it should begin to ascend, since, for ought he shews to the contrary, the pressure of the Air, even in the sense he takes the Air, ought to be the same on that part of the Surface of the Liquor which is contiguous to the Filtre, and on any other part of the same Surface. To which I shall [Page] onely adde, that as resolutely as Mr. Hobbs sayes 'tis impossible for the water to ascend out of the Vessel into a Siphon, unless both the legs be fill'd with that Liquor, he would probably have spoken more warily, and distinguish'd betwixt Siphons, if he had been pleased to take notice of what I relate in the-forementioned 35. Experiment, of a small Glass-Siphon I devis'd, whereof when the shorter leg was but dipp'd in water, the Liquor did presently as it were of it self run down the longer leg. Which Experiment, besides other considerations, may induce us to suspect that the nature of Siphons and of Filtration may not yet be so throughly understood, as not to deserve a further enquiry.

But to draw at length towards a Conclusion of our troublesome Examen; it remains onely that I take some notice of the general Corollary that Mr. Hobbs is pleased to deduce from his whole Discourse, of the Experiments exhibited in our Engine.

A. Fateris ergo (says he) nihil hactenus à Collegis tuis promotam esse scientiam causarum naturalium, Page. 23. nisi quod unus eorum machinam invenerit qua motus excitari aeris possit talis, ut partes sphaerae simul undiqua (que) tendant ad centrum, & ut Hypotheses Hobbianae, ante quidem satis probabiles, hinc reddantur probabiliores.

B. Nec fateri pudet; nam, Est aliquid prodire tenus, si non datur ultra.

A. Quid tenus; Quorsum autem tantus apparatus & sumptus machinarum factu difficilium, ut eatenus tantum prodiretis quantum ante prodierat Hobbius? cur non inde potius incepistis ubi ille desiit? cur principiis ab eo positis non estis usi? Cum (que) Aristoteles recte dixisset, Ignorato motu ignorari naturam, quomodo tantum in vos suscipere onus ausi estis, &c.

As to what he sayes to the disparagement of the Assembly, and in his own praise, the laws I prescribed my self at the beginning of this Discourse forbid me to reply to what is more likely, amongst civil and judicious Readers, to prejudice his own reputation than theirs he is so displeased with. [Page] And as for that which he assigns to be the use of our Engine, I shall very willingly leave it to the ingenious to judge what use may be made of it. But as for this mentioned by Mr. Hobbs, if he means here, as he elsewhere teaches (pag. 13. and 19.) that the Motion he speaks of is produc'd by that of the Air impell'd betwixt the sides of the Sucker and the Cylinder; perhaps it will be thought I have sufficiently proved, that 'tis not any of its uses, so far is it from being its chief or onely use. But I consess I somewhat wonder Mr. Hobbs should quarrel with me, (for 'tis I that in my Epistle employ the following Verse) for saying,

Est aliquid prodire tenus, si non datur ultra.

And this not, as some would perhaps suspect, because I do not imitate him, in speaking of my self, as he does of himself, but because he thinks the expression too arrogant. For since he here confesses that his Hypotheses are by this Engine rendered more probable, some will perchance think that to be enough to entitle my Experiment to some degree of usefulness, unless Mr. Hobbs's Doctrine of the Air had found more embracers than before these seasonable, though despised, Experiments it was observed to have. But, since either of us may be partial in his own case, I am very well content to leave others to judge both whether my Expression have been guilty of Arrogance, and how much he has done more than prodire tenus in all the past long Discourse against me, when they have considered what new Experiment or matter of fact Mr. Hobbs has therein added to enrich the History of Nature, what new Truths he has discovered, or what Errors (except one of his own in the last page) he has well confuted. These things, I say, I am very well content to leave to be judged of by all dis-interessed persons, without being much discouraged by the differing strain wherein Mr. Hobbs thinks fit to speak of his own performances and mine, or invited to imitate him in that way of writing, my Endeavours (such as they are) having hitherto been favoured [Page] with such a Reception among the Virtuosi, that possibly I may have almost as little need as reason to commend them.

But 'tis somewhat trouble some work to argue long with a man that's angry with an Expression, which perhaps none but he would have found fault with for want of modesty; and therefore as I have lest un-recited several provoking and very undeserved Expressions he emploies in the same page, and even that passage, where to prove our Naturalists and Mathematicians professed they would not receive Truth coming from him, he alledges onely a saying (whether true or no I examine not) of Dr. Owen, who, besides that his profession was Divinity, not Philosophy or Mathematicks, neither is nor ever was of our Society; as, I say, I have (for the reason newly intimated) declin'd taking notice of matters of this nature; so I will not now stay to enquire why he urges us, whom he would have men take for Vacuists, with the Authority of Aristotle, whom on other occasions he is wont to use with as little respect as if he were a Member of our Society. Nor shall I now examine, why here and elsewhere he sends us to his own Writings for the Doctrine of Motion, as if, to omit ancienter Authors, such great Personages as Galilaeo, Mersennus, Verulam, Des-Cartes, Gassendus, Balianus, Foannes Marcus Marci, Honoratus Fabris, (not to mention other Moderns, nor those of our own assembly, as the eminently learned Sir Kenelme Digby, and the others, whom their Modesty forbids me here to name) had not most of them learnedly, and some of them copiously, written of Local Motion before Mr. Hobbs's Books, where he treats of it, came abroad into the World. This, I say, I shall not insist on, because I would hasten to a Conclusion. Onely one thing I must adde, that whereas he accuses us of devising elaborate and sumptuous Engines, I do not fear to find so many Readers of his mind, that I need make them Excuses for what perhaps will obtain their Thanks. And whatever Mr. Hobbs may think, for my part I freely confess, that I love Truth so well, that I do not think, no [Page] onely my Pains and Charges, but even what I rate much higher, my Time it self, too much for the discovery of Truth; or (that Mr. Hobbs may not think me partial) even for the establishment of such Truths as, though discover'd by some, are yet as far more generally opposed than imbraced.

There remain yet some other pages of Mr. Hobbs's. Dialogue, wherein he speaks of Fire, and Cold, and Ice, and Light, and Colours, and Fluidity, and Hardness, and Thickness, and Ethicks, and Politicks, and the Duplication of the Cube, and the Quadrature of the Circle, and several other Subjects. But these I forbear to meddle with, not that I approve them all, or the greatest part, but partly, because I am too much tired already to be fond of engaging in Controversies that I am not tyed to meddle with, (except what concerns Fluidity and Firmness, which I shall, God willing, examine by it self;) partly, because divers passages relate to Persons, not Things: partly, because I do not much fear that Mr. Hobbs will find every Reader so easie and complaisant as he makes his Academian, who in many passages of the Dialogue speaks not unsutably to what he does in the last page ofit, where he excepts but one particular (and that is neither the Duplication of the Cube, nor the Squaring of the Circle) when he tells Mr. Hobbs, Discedo jam multo (ut mihi videor) quam ante certior, & quae dixifti omnia teneo & probo: and partly, because Mr. Hobbs has some things, as about Fire, and certain Colours, which I am not forward to reject, though the Considerations that incline me to some such Opinions be perhaps very differing from the Grounds on which he proposes them. And indeed as well my Nature as my Custom forbids me to scruple to learn, if I can, of Persons much less famous than Mr. Hobbs. 'Tis far from my humour to write against all that every man sayes, that (how causlesly soever) writes against me; and I am almost as much indisposed to reject as to embrace, without distinction, whatever it be that this or that man teaches.

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CHAP. VII. (Being an APPENDIX to the past Discourse) Wherein is examin'd what Mr. Hobbs teaches concerning Fluidity and Firmness.

ALthough Mr. Hobbs do not name me for the Maintainer of the Opinions which I have proposed in the History of Fluidity and Firmness, and which he censures: yet since that History, after having been mentioned in the Book I have hitherto been defending, was published a good while before Mr. Hobbs's Dialogue; and since some of the chief particulars he censures or takes notice of, are delivered there, and some of them perchance no where else; I think it may concern me to examine what he sayes either against my Opinions, or in favour of his own, touching Fluidity and Firmness. And if it be said that he meant not his Objections particularly against me, but rather against some other person, who may have liked such Opinions: I shall answer, That I am content to leave to others the defence of their particular Opinions, and to have as much of the following Discourse as is concerned in this Allegation, looked upon as written onely upon this supposition, that my writings are those he designs to oppose. But there being other things in what he discourses about Fluidity and Firmness, which for the reasons freshly intimated I think fit here to consider, I chuse to gather up together the passages touching these subjects which I find scattered in his Dialogue, that I may have the better opportunity to clear up the matter it self under debate.

But, before I go further, I must at the very entrance of this Discourse take notice, that in the fifth page, where Mr. Hobbs begins to dispute against our Notion of Fluidity, he very much mistakes my Opinion, as may appear by these words, which he puts into the mouth of his Academian, Sed pleri (que) nostrum naturam fluidam à non fluida distinguimus Page 5. magnitudine partium ex quibus corpus aliquod constat, & quasi compingitur: Ita (que) non modo aërem; aquam & liquorum[Page]omnem, sed etiam cinerem & pulverem, tanquam fluida contemplamur. Et fluida ex non fluidis composita esse posse non negamus; nam divisibilitatem illam infinitam non concoquimus. To which he answers, Divisio quidem infinita concipi non potest, divisibilitas autem facile. Ego contra, distinctionem non capio intra fluida & non fluida quam sumitis à magnitudine partium; nam si caperem, ruina illa sive rudera illa quae jacent in Ecclesia Paulina mibi dicenda essent fluida: sin propter nimiam lapidum magnitudinem fluida illa esse negaveritis, defini mihi magnitudinem illam quam habens pars ruentis muri, propter eam sit dicenda fluida. Tu vero qui divisibilitatem infinitam non capis, dic mihi quae tibi apparet causa, quare Deo omnipotenti difficilius esse putem creare corpus fluidum, & cujus partes actu diffluant, omni data atomo minus, quam creare Oceanum. Ita (que) desperare me facis omnem conventus vestri fructum, dicendo quod putant aërem, aquam, & caetera fluida constare ex non fluidis, tanquam si murum, cujus ruentes lapides aliquous (que) discurrunt, dicerent esse fluidum. Si sic loquendum est, nihil non est fluidum; nam etiam marmor comminui potest in partes omni atomo Epicureana minores. Thus he. But in my History, though I make the smalness of the parts whereof a body consists one of the requisites to its being fluid; yet at the end of the 13. Section I call the various agitation of those Particles the principal qualification of all, and in the beginning of the 14. Section I call it the cheif condition of a fluid body. And therefore he much mistakes, if he thinks that we alwayes consider Ashes and Dust as fluids absolutely speaking. But as he Hobbs de Corp. ch. 27. somewhere tells us, that by Fire he understands the combustible matter it self, not simply and alwayes, but then onely when, &c. So neither do I look upon the Dust of Alabaster, (to my words about which, I suppose, he has a respect in the passage under consideration) as a fluid body simply and alwayes; for I clearly teach the contrary, but onely when and whilst its parts are not alone reduced to a competent smallness, but are also actually put into such a various agitation as [Page] makes the body they compose (even according to Mr. Hobbs's own Definition, which is, That Fluid bodies are those whose parts may by very weak endeavour be Mr. Hobbs de Corpore, cap. 26. part. 4. separated from one another) emulate a fluid body by the very easie Cession of its component Corpuscles, and by its boyling like a liquor. By this the Reader may discern how little that makes against me which Mr. Hobbs talks, and seems to do it seriously, of the Ruines of Pauls; as if according to my Opinion, Ruina illa sive rudera a quae jacent in Ecclesia Paulina dicenda essent fluida. For 'tis most evident that I require in the parts of a fluid body both minuteness and such a motion along each other as makes them easily yeild to the touch: which qualifications how well they belong to the ruines of Pauls, is, I think not very difficult to determine; though in the same passage Mr. Hobbs do again make use of the like example, to which he subjoyns. Si sic loquendum est, nihil non est fluidum; which how little it follows from my Doctrine about Fluidity there needs not a quick-sighted Reader to discern. As for the Reason he annexes in these words, Nam etiam marmor comminui potest in partes omni atomo Epicureana minores; I would gladly know by what art Mr. Hobbs can divide Marble into lesser Particles than such as are naturally indivisible, (for such Epicurus makes his Atoms to be:) nor do I see how, in case this could be done, it proves, that there is not any thing that is not fluid. For I say that the blocks of Marble before Comminution are not fluid, either according to him or according to me; nay, the greatest Comminution imaginable would not, according to my Doctrine, make a lump of Marble fluid, unless the heap composed of the parts, how minute soever, were actually and variously set a moving amongst themselves. But he would perhaps have spoken more warily, if he had considered the difference there is betwixt saying that all things are fluid, and saying, as I do, that there are many bodies that are now solid, which by Comminution, Motion, and other requisite alterations, may be made parts of a fluid body: [Page] As hard Ice may be turned into fluid Water, and Quicksilver precipitated per se into a red Powder, may be reduced to running Mercury. As for what he sayes of an infinite divisibility of body, it is scarce in this place worth while to examine it.

For I have shewn in the History of Firmness, that this Divisibility (which I had then considered) does no way overthrow my Doctrine of Fluidity; nor does Mr. Hobbs here answer what I there discourse. Besides that indeed I donot so well understand what he means and drives at, when he sayes that Divisio quidem infinita concipi non potest, Divisibilitas autem facile. For since in this very passage and within a very few lines he has recourse in this matter to God's Omnipotence, I see not why an infinite division cannot be as well conceived as an infinite divisibility, since sure an Omnipotent Agent is able to do what is possible to be done; and why else should a body be called infinitely divisible? Besides, when Mr. Hobbs has recourse to what God can do, (whose Omnipotence we have both great reason to acknowledge) it imports not to the Controversie about Fluidity to determine what the Almighty Creator can do, but what he actually has done. And, lastly, whereas my Adversary requires to have the magnitude defined which a part of a falling Wall ought to have to deserve the name of fluid; first, he should have clearly proved that Fluidity belongs to any one single part of matter how minute soever, and not rather to an aggregate of Particles. And next I say those Corpuscles that compose a fluid body may be of several sizes, as those of Water, Oyl, and Quicksilver, provided they be little enough to be put into the agitation requisite to give the aggregate they make up the qualities that are wont to denominate bodies fluid; and 'tis no more requisite for me to define precisely the magnitudes of the parts of a fluid body, than for Mr. Hobbs in his Definition above-recited to define (which he will not easily do) what precise degree of endeavour must be signified by that very weak endeavour, by which if the parts of a body can be separated [Page] from one another, he thinks fit to call them fluid. But though I thought it not amiss to make these Animadversions upon Mr. Hobbs's Ratiocination, yet as to the Opinion it self, for whose sake he speaks so severely and so despairingly of our Society, if it be considered as I propos'd it, he shews me as yet no cause at all to renounce it. For that which I taught is this, That if a solid body be reduc'd into parts minute enough, those solid Corpuscles, whilst they are put into a convenient motion, may become parts of a fluid body. And against this Mr. Hobbs's indignation seems stronger than his Argument: For that which he objects being as we have lately seen, that at this rate all bodies must be fluid; 'tis evident by what I have already argued, that he infers this Absurdity not from my Opinion, but his own mistake of it: nor did I content my self with the proofless proposal of my Conjecture, but I delivered in several parts of the often mention'd History particular Experiments to evince what I taught: As that a consistent coagulum of pure spirits of Urine and Wine may by bare digestion be turned into a permanent liquor; and that the fluid body of Quicksilver may without any sensible addition be turned into a permanent dry Powder, and may again in a trice by bare heat be turned into a lastingly fluid body. Whereto I added other Experiments, which together with these Mr. Hobbs would possibly have thought fit to answer, if he had found it easie for him to do so.

After this passage extant in Mr. Hobbs's fifth page that I have all this while been examining, I remember nothing in his Dialogue that requires to be insisted on about Fluidity and Firmness, till we come to the 29. page, where having asked what cause the Academians assign of Hardness, 'tis answered that some of them assign three: to which Mr. Hobbs so far agrees as to say, Quin corpuscula (qualia sunt atomi quas supponit Page 29. Lucretius at (que) etiam Hobbius) jam ante dur a facile possint ab aliqua dict arum causaram compingi, it a ut totum ex illis factum durum fiat, dubitandum non est. But then he would have us assign the cause of that he calls durum primum. But after some discourse, wherein he is pleased to approve an Objection of mine against some learned men that ascribe all Cohesion of bodies to a [Page] certain Glue, he answers himself the Objection he frames against my Doctrine about Hardness, and thereby allowed me to proceed to what he further presses in these words, Si dura ex primis duris fieri dicant, quare non & fluida fieri putant ex primis fluidis? An creari fluida maxima potuere, ut aether, minima Page 30. non potuere? Qui Corpusculum durum aut fluidum primus fecit, potuit, si libuisset, illud fecisse tum majus, tum minus quocun (que) corpore dato. Quod si fluidum fiat ex non fluidis, ut vos dicitis, & durum ex duris tantum, nonne sequitur ex fluidis primis ne (que) fluidum fieri ne (que) durum? But against this passage I have divers things to represent. For, first, (not now to mention that it may be questioned with what propriety one part of matter more than another may be called primum durum) he should have told us what he means by his prima fluida, and how he proves that there are any such; which since he has not done, 'twill be at least as hard for a considering man to acquiesce in his Question as to answer it. For my part, I know no fluid body upon whose account, as of an Ingredient, all others are fluid. And, I think, 'twill be hard for Mr. Hobbs to shew that Water, Quicksilver, and purely-rectifi'd Chymical Oyles (to name now no other liquors) do consist of such fluida prima as he teaches, whereto they owe all their Fluidity. And 'tis plain by several Experiments delivered in our History, and even by the obvious changes of Water and Ice into one another, that 'tis the motion, rest, and the texture of the Corpuscles which compose a Body, that make it firm or fluid. As for what Mr. Hobbs demands, whether the smallest Fluids imaginable could not as well have been created as the AEther, it proves nothing against me, the Question not being, what might have been made, but what is so. And he should have answered the Arguments I History of. Firmness, page, 227. and elsewhere. alledge to make it improbable that a fluid body is, as he would perswade us in his Book Chap. 16. Sect. 4. De Corpore, alwayes divisible into bodies equally fluid, as Quantity into Quantities. 'Tis true, he there tells us that, though many others do not, He understands by Fluidity that which is made such by Nature equally in every part of the fluid body, in such manner as water seems fluid, and to divide it self into parts perpetually fluid. But whether [Page] others will take this for a clear Notion of Fluidity I think may well be doubted; and he should not barely say, but prove, (which, I think he will find hard to do) that the Corpuscles of water divide themselves so as he teaches, since we see, that not onely they cannot penetrate Glass, but are unable to be driven in at the Pores of more open bodies, which other liquors easily pierce into. And, lastly, as to Mr. Hobbs's Question, Quod si fluidum fiat &c. 'tis easie to foresee what according to my Doctrine I may answer: For, not to mention that the Argumentation is invalid, unless by Fluidum he mean Omne fluidum, I reply, That till he have explained what he means by his Fluida prima, and proved that there are such, the Question needs no Answer. Besides that whatever he upon mistakes strives to infer, my Doctrine is so far from affirming that there are many parts of matter of which neither fluid nor hard bodies can be made, that I teach, as we have lately seen, that there are multitudes of parts that may, by being reduced to a sufficient smalness and put into a convenient motion, or by being brought to a mutual contact and rest, be made to constitute either a fluid body or a firm one: as may be exemplified in the formerly-mentioned instances of two subtile liquors that immediately composed a consistent body; and of Quicksilver, which without additaments was made sometimes a Powder, and sometimes a liquor. What Mr. Hobbs addes in the next page about the difficulty of explaining the Diaphaneity of Glass or Crystal, in case they Page 31. consisted of Corpuscles hard and implicated, or having their Pores in any way whatsoever disjoyned, I must not now insist on; since besides that such a disquisition would require almost a Volume, the true and general cause of Transparency in bodies is in my poor Opinion one of the abstrusest things in Natural Phylosophy; and Mr. Hobbs's Explication of it (though none of his worst Conceits) has for ought I can find fallen short of satisfying the Curious, as well as those of other men have done. But to me, that have not taken upon me to write Elements of Phylosophy, it is enough that I have by competent Experiments and other Proofs confirm'd the truth of my Doctrine about the cause of Firmness; though I attempt not to explicate the other qualities [Page] of the same bodies, whose Explication my undertaking does not exact. Wherefore I hope I may now hasten to conclude this Appendix, with spending a few words on the Notion of Fluidity and Firmness Mr. Hobbs would substitute instead of mine. For, having now (perhaps but too prolixly) examined what he has been pleased to object against my doctrine, I shall not need spend time to vindicate the Experiments and Considerations whereon I built it, Mr. Hobbs, for reasons best known to himself, not having thought fit to take notice of them.

Mr. Hobbs's Theory of Fluidity and Firmness is thus delivered by himself;

B. Quaenam duri & fluidi sunt principia?

A. Quid aliud nisi fluidi quidem, Quies, duri autem, Page 30. Motus quidam ad illum effectum producendum idoneus? Per Quietem intelligo duar am partium inter se quietem cum se mutuo tangunt quidem, sed non premunt: Nam & fluida moveri tota possunt retenta fluiditate, & dura quiescere, ut tamen partes eorum moveantur.

I doubt not but this will to most Readers seem a Paradox. And as for his Ratiocination contain'd in the two last lines, I shall readily allow him that Fluida moveri tota possunt retent a fluiditate, since that I think agrees at least as well with my Hypothesis as his: but whereas he adds that hard bodies may rest, and yet their parts be moved, that may in one case be conceived, and in another not. For indeed the implicated parts of a firm body may be made to tremble or a little vibrate as it were to and fro, as those of a sounding Bell do, or as in a Hedge the branches and twigs may be shaken by the wind, whilst the trees and bushes themselves continue rooted in the ground. But that in a body the constituent Corpuscles should all or most of them be moved quite out of their places in respect of one another, as was lately shewn to happen in fluids, and yet the body continue hard, is more requisite than easie to be proved.

But Mr. Hobbs contents himself to alledge in favour of his strange Notion touching Fluidity and Firmness three particulars, which, I confess, afford me not the least satisfaction.

The first is drawn from what he formerly taught touching the [Page] swift motion of the Air in our Cylinder; which example (as he calls it) having repeated, he adds, At (que) hinc manifestum est vehementem esse in aëre it a moto & clauso compressionem, Page 30. quantam scilicet efficere potest vis illa qua incussus erat; at (que) etiam à tanta compressione aliquem gradum consistentiae fieri, quanquam consistentia aquae minorem. Quod si esset in iisdem particulis aëris omnibus, praeter motum illum quo alter a alteram premit, motus ille circularis simplex, is (que) satis vehemens, impossibile fere esset unam earum à suo circello dimoveri, quin reliquis particulis resistentibus, totus simul premeretur, idest, totum durum esset: durum enimest totumillud, cujus nulla cedit parsnisi cedente toto. Vides ergoposse fieri duritiem in fluidissimo aëre per motum hunc circularem simplicem particularem, quibus duo motus contrarii ante dederant vertiginem.

But, I confess, I do not see how the Motus circularis simplex he talks of should give such a hardness to the fluid Air: nor is it manifest to me how the Air that perfectly fills the Cylinder can be by motion compress'd, especially so far as to obtain thereby a degree of consistence fit to be mentioned, as he speaks of it, when (without adding the word much, or any other equivalent term) he sayes that yet 'tis less than the consistence of water. For the Cylinder being, according to him, perfectly full of Air, I see not how the Pumping can make the Cavity (to use his own expression elsewhere) fuller than full; nor consequently can compress the Air to a consistence any thing near that of water, without penetration of Dimensions. But these things were mentioned onely ex abundanti, for the violent motion it self of the Air in the Cylinder (which motion the Argument supposes) has been already, in the Examen of one of the former passages of his Dialogue, sufficiently manifested to be contrary to Experience.

The second thing Mr. Hobbs alledges is his Conceit of the Generation of Flesh within the Muscles of the humane body. But besides that he takes for granted two or three things which many learned Anatomists and Physicians, even among the Moderns, will scarce allow him, and which he does not prove: besides this, I say, (which I may elsewhere have occasion to consider further) the account he gives of the Generation of Flesh from these suppositions, is far from being evidently enough deduc'd [Page] to vie for clearness with many of those Experiments which I have alledged in favour of the Opinion he opposes. And whereas he adds, At (que) talis quidem esse potest causa efficiens Duri primi, Duri autem secundi, id est, Duri à cohaesione Page. 31. durorum primorum, causa potest esse motus ille idem circularis simplex conjunctus cum contactu eorundem superficiali, vel etiam intricatione: Not again to say any thing to his durum primum, I confess I do not see how the motus circularis simplex should need to be superadded to the Contact or Intrication of the cohering firm Corpuscles, to procure a Cohesion, to which'tis needless, and which in divers cases may be rather hindered than furthered by it.

The third thing that Mr. Hobbs alledges is not so much a confirmation of his own Doctrine, as an Objection, as he seems to think, against that of his Adversaries. For, Si supponamus (sayes he presently after his last-recited words) Page. 31. cum illis, duritiei causam esse magnitudinem aut crassitiem partium, quam rationem reddere poterimus, cur durior vel firmior sit aqua congelata, quam est eadem aqua ante congelationem? But it may easily be replyed, That we make not the bigness or grosness of the parts of a body the onely or chief cause of its hardness, but their rest by one another, which the parts of frozen water have; whereas those of unfrozen water have it not, but are in a state of Fluidity, and consequently not of Firmness. Which may be illustrated by what I In the History of Fluidity and Firmness. elsewhere relate of pure Oyle of Aniseeds, and a substance I distilled out of Benzoin, both which bodies were sometimes fluid and sometimes consistent, as the greater or lesser warmth of the Air kept their parts in a due motion or suffered them to rest.

But in exchange of these few & unconcluding arguments, which are all that Mr. Hobbs alledges to countenance his Paradox, how many Experiments and Reasons mightwe transcribe out of our History of Fluidity and Firmness in favour of the contrary Truth?

And as Critical as Mr. Hobbs appears in laying down the requisites of a good Hypothesis, I must make bold to the two conditions he mentions (pag. 11.) Vt sit conceptibilis (idest, non absurda) (which whether it be enough I now dispute not) & Vt ab [Page]ea concessa inferri possit Phaenomeni necessitas, to adde a third, namely, That it be not inconsistent with any other Truth or Phaenomenon of Nature. Which third condition whether divers of Mr. Hobbs's Hypotheses (which himself in this place calls mirandae) do not want, we have in part already considered in the Treatise to which this is an Appendix; and (as I newly intimated) I might further shew as to his Notion of Fluidity and Firmness, if I would here repeat all the Experiments mentioned in my History of them, though they be not all that I have made ready to the same purpose against another opportunity: but partly weariness, and partly a natural unwillingness to repeat, induces me rather to refer my Reader thither. Which when I do, I do not forget that Mr. Hobbs appears offended at me and others for troubling our selves to make un-obvious Experiments. But that I may not repeat what in divers Treatises I represent concerning the Usefulness of such Experiments, I shall now onely oppose to the Authority of Mr. Hobbs in this Dialogue, wherein he has been pleased to chuse those he calls the Experimentarian Philosophers for his Adversaries, the Authority and Reason of the same Mr. Hobbs in another Dialogue (published but the year before) where one of his two Discoursers having said, Qui corpora corporibus admovendo, nova & mirabilia ostendunt Naturae opera, mirum in modum incendunt animos hominum Mr. Hobbs in Examinat. & Emendatione, &c. Dialog. 6. amore Philosophiae, & ad causas investigandas non parum instigant, eo (que) nomine laude digni sunt: the other confirms it by adding, It a est; nam historiam Naturalem (sine qua scientia Naturalis frustra quaeritur) locupletant. And howsoever Mr. Hobbs needed not have recourse to such Experiments as he would be thought to disapprove, (I mean Elaborate ones) to discern that his Notions do not over-well agree with the Phaenomena. For, if there be not a various motion in the small parts of Water and such liquors, whence is it that a lump of common Salt being thrown into a pot of water is there dissolved into minute bodies, whereof many are carried to the very top of the water, and are so exquisitely diffused and mingled with the liquor, that each least drop of it contains numbers of Saline Corpuscles? And if motion be the cause rather of hardness than fluidity, how [Page] comes it to pass that in frosty weather Ice is by heat (which Mr. Hobbs will not deny to be motion, or an effect of it) turned from a hard to a fluid body? And that Metals, as Gold and Silver, &c. whilst they are either cold, or exposed but to a moderate heat are firm and consistent bodies; and by a violent heat, which does manifestly give their parts a various and vehement agitation, (as appears by their sudden dissipating of Spittle, Greace, and far more stable bodies, cast upon them, into smoak) are put into a fluidity, which upon their removal from the fire they quickly exchange for firmness?

But since the want of more to say would not in haste put a Period to this Discourse, I am content to let my Haste break it off; especially since after I have thus examined what Mr. Hobbs teaches concerning Fluidity and Firmness, either here, or in that Section of his Elements where he pretends to define them, I think I need not fear that a Doctrine which I have perhaps with some care endeavoured to establish, for the main, upon Experiments, should be overthrown by Opinions whose grounds are but such as we have already seen; and in pleading for which the Author is pleased not onely to leave almost all my Arguments untouch'd, but not so much as to offer at explicating by his Principles any of those numerous and important Phaenomena of Fluidity and Firmness delivered in the Treatise he opposes.

And now leaving Mr. Hobbs to apply my self to the Reader, I have to the things hitherto discourst but this one thing to adde concerning them, That as little cause as Mr. Hobbs has hitherto given me to distrust what I have written of Fluidity and Firmness; yet I am not now more confident of my Conjectures than I was, when toward the end of the Preface to the History of these two Qualities I spoke diffidently enough of the Theorical part of that Treatise. And I freely confess, that the great difficulty of things, and the little abilities I find my self furnisht with to surmount it, do often in general beget in me a great distrust even of things whereof my Adversaries Objections give me not any.

FINIS.

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The Citations English'd

PAg. 12. Quanquam vis, &c. Although the force of that motion in the evacuated Receiver be diminished, being opprest by the consistence of the Air moved within, yet it is not extinguished: and therefore that oppression being taken off will have strength enough to excite an appearance of light, though somewhat weaker than ordinary.

p. 13, 14. Sine, &c. Without which Hypothesis let never so much labour, art, cost be bestowed for the finding out of the invisible causes of natural things, all will be in vain.

p. 15. Cum ejus, &c. Seeing almost all its parts are flexil, like little soft feathers to fine threds.

Ibid. Sed quisquis, &c. But it matters not who was the Author of that Supposition. For the very Hypothesis it self, wherein is supposed a motion of subtil matter, which is swift without any cause assigned, and hath moreover divers innumerable circulations of Corpuscles generated from the single motion of that matter, is not the conceipt of a man of wit or sense.

p. 16. Nempe hoc, &c. This is the thing that the great Des-Cartes somewhere admired, that he, whether his Positions are true or false, doth never in argumentation make any right inference from his Suppositions.

p. 17. Quod sane, &c. Which is indeed a most evident argument of the weight of the Air.

Ibid. Quod quidem lanx, &c. That the Scale in which the Bladder is, is more deprest than the other, they may be certain, their eyes bearing them witness: but that this comes from the natural gravity of the Air he cannot be assured; especially if they are ignorant what is the efficient cause of Gravity.

p. 18. Quod vesica, &c. That the Bladder, whether it be blown up with a pair of Bellows, or with the breath of ones mouth, is heavier than when it is not blown up, I will not deny, because of the greater quantity of Atoms from the Bellows, or of fuliginous Corpuseles that are blown in from the breath. But notwithstanding they gather nothing of sufficient certainty from this Experiment of a blown Bladder. They ought to have put into the Scales two Vessels of equal weight, whereof one should be shut and the other open: For by this means Air not blown in, but onely inclosed, had been weighed. When therefore you shall see Air so weighed, we will afterwards consider what may be said concerning the Phaenomenon you bring.

[Page]p. 19. Quod Atmosphaerae, &c. That many Particles both of Earth and Water mingled with the AEthereal body are in the Atmosphere, I am easily persuaded: but that in the middle of the AEther they should move upwards, downwards, every way, and that one leaning on the back of another they should not gravitate, is a thing utterly unconceivable.

p. 20. Aer quo, &c. The Air, with which in the beginning the Spherical Glass was full, being moved by those Earthy Corpuscles in a simple circular motion, and being comprest by the force of the Injection, that of it which is pure (penetrating the injected Water) gets out into the open Air, and gives place to the Water. It follows therefore that those earthy Corpuscles have less place left, in which they can exercise their natural motion: therefore beating one upon another they force the water to go out; it thus going out, the external Air (because the Universe is supposed to be full) penetrates it, and successively takes up the place of the Air that goes out, until the Corpuscles, the same quantity of Air being restored, regain a liberty natural to their motion.

p. 21. Quoniam, per, &c. Because by the drawing back of the Sucker the pure Air was thrust in, but the earthy parts were not thrust in; there was a greater proportion of earthy Particles, which without the Cylinder were near the Sucker, unto the pure Air, in which they exercised their motion as well after this revulsion as before. Wherefore these Particles so moved having less place to exercise their natural motion in, some of them fell foul and beat upon the rest. So that of necessity the Particles that were near the surface of the Sucker must drive it upwards.

Ibid. Vidisti, &c. You see now that the Spring of the Air, which they fuppose, is either an impossible thing: or they must (for its defence) have recourse to the Hypothesis of Mr. Hobbs.

p. 23. Quia cuticula omnis, &c. Because every skin is made up of small threds or filaments, which by reason of their figures cannot accurately touch in all points. The Bladder therefore, being a skin must be pervious not onely to Air but to Water also, as to sweat: Therefore of the Air beat in by force there is the same compression within the Bladder that there is without. The endeavour of which, the way of its motions being every way cross, tends every way to the concave superficies of the Bladder. Wherefore it is of necessity that it must swell every way, and the vehemency of the endeavour increasing, be torn at last.

p. 26. Intellexti, &c. Have you understood my Hypotheses? 1. That there are with the Air intersperst many earthy Particles, endued with a simple circular motion, congenite to its nature. 2. That there is a greater quantity of these Particles in the Air that is near the Earth, than in that which is more remote from it.

[Page]p. 27. Ne (que) est, &c. nor is there any one that hitherto has brought any reason why it may not be so.

p. 29. Nihil, &c. Nothing is moved but by a contiguous Body that is in motion.

Ibid. Dum Suctor, &c. While the Sucker is drawn back, by how much a greater place is left (within,) by so much a lesser place is left to the external Air, which being thrust backwards by the motion of the Sucker towards the outmost parts, doth move in like manner the Air that is next it self, and that Air the next, and so forwards; so that it is of necessity at last that the Air must be compell'd into the space deserted by the Sucker, and to enter between the convex and surface of the Sucker, and the concave of the Cylinder. For it being supposed that the parts of the Air are infinitely subtil, it is impossible but they should insinuate themselves that way by which the Sucker is drawn down. For first, the contact of those surfaces cannot be perfect in all points, because the surfaces themselves cannot be made infinitely smooth. Then, that force which is applied to draw back the Sucker, doth distend in some measure the cavity of the Cylinder. Lastly, if in the confines of (that is, betwixt) the two surfaces any one single hard Atom should enter, pure Air will enter at the same way, although with a weak endeavour. I might also have accounted that Air which for the same cause insinuates it self through the Valve of the Cylinder. You see therefore the consequence from the retraction of the Sucker, to the being of an Empty place is taken away. It will follow also that the Air which is driven up into the place deserted by the Sucker, because it is driven up thither by a great force, is moved with a very swift and circular motion betwixt the top and the bottom in the Cylinder, because there is nothing there that can weaken its motion: and you know that there is nothing that can give motion to its own self, or diminish it.

p. 39. Haerent hic, &c. Here our men are at a stand: How will you expedite this difficulty?

A. I have don't already: For the Air being beaten back by the retraction of the Sucker, and finding no place in the world (which we suppose to be full) where it might dispose it self, besides that which by driving out other bodies from their places it may make for it self, is by perpetual pulsion at length forced in the Cylinder with so great swiftness, between the concave surface of the Cylinder and the convex surface of the Sucker, as may answer that store of power which you found necessary to the drawing back of the Sucker. Now the Air, with what swiftness it enters, retains the same within, and then distends every way the sides [Page] of the Brass Cylinder, which is (of it self) Elastical. Therefore the Air in the Cylinder being vehemently moved, endeavours or thrusts against all parts of the concave surface of the Cylinder; but in vain, untill the Sucker, is drawn back: But as soon as the Sucker having slipt the hand, ceases to make its impulse upon the Air, that Air which was before driven in, by reason of its endeavour against every point of the internal superficies of the Cylinder and of the Elastical force of the Air, will insinuate it self between the same surfaces with the same swiftness as that by which it was impell'd, that is, with that velocity which answers the strength of the impulsion. If therefore so great a power of Weight be hung upon the Sucker as may answer the power of the hands by which it was impulss'd; the swiftness with which the same Air goes out of the Cylinder, finding no place in the world (which is full) where to dispose it self, will again impell the Sucker to the top of the Cylinder, for the same reason that the Sucker a little before made an impulse upon the Air.

p. 44. In vas, &c. B. We poured water into an open Vessel, we placed in the water a long, streight, slender Tube; and we observed that the water did ascend from the Vessel underneath into the erected Tube.

A. No wonder: For the small Particles that are interspers'd in the Air near the Water, did by their motion beat upon the surface of the Water, so that the Water must of necessity ascend into the Pipe, and that sensibly into a Pipe that was so exceeding slender.

p. 45. Siquis, &c. If any one after the frequently-repeated impulse and retraction of the Sucker, endeavour to draw out the Stopple of the upper Orifice of the Receiver, he shall find it gravitates very much, as if a weight of many pounds hung upon it. Whence comes this?

A. From a strong circular endeavour of the Air within the Receiver, made by the violent ingress of the Air between the convex surface of the Sucker and the concave of the Cylinder, procured by the repeated impulse and revulsion of the Sucker, which you improperly call the Exsuction of the Air. For by reason of the fullness of Nature the Stopple cannot be drawn out, but the Air that is in the Receiver (contiguous to the Stopple) must be drawn out too: which Air, if it were settled and at rest, the Stopple would easily be drawn out; but whiles that doesmost swiftly circulate, it comes out very hardly, that is, it seems to be very heavy.

B. Very likely: For as soon as fresh Air is by degrees let into the Receiver, it likewise by degrees loses this seeming gravity.

p. 47. Vidimus, &c. We saw also water, being let down into the Receiver, after some returns of the motion of the Sucker, to bubble so as if it had boiled over a fire.

[Page] A. This likewise happens, as we spake, by reason of the swiftness of the circulating Air: unless perhaps you find the water hot too whiles it bubbles. For if we were sure it was hot, we must find out some other cause of the Phaenomenon.

B. We are certain it is not sensibly hot.

A. In what therefore can the greater or lesser motion of the Atmosphere promote such a motion as this?

B. I suppose they do not attribute this motion to the Atmosphere.

p. 49. A. It is manifest from this Experiment, that the Receiver is not made empty by this exsuction of Air, as you call it: For the water could not be moved but by some contiguous mover, that was it self in motion. Therefore this Phaenomenon seems to contain no weak demonstration of my Hypothesis.

p. 50. Besides, tell me, could you see the water bubbling in that manner?

B. What else?

A. Do not your Associates grant that Vision is made by a continued action from the object unto the eye? Do they not also think action to be motion, and all motion to be of some body? How therefore could the motion be derived from the object, the water, unto your eyes through a Vacuum, that is somewhat that is not a body?

B. Our friends do not affirm the Recipient to be so empty that no Air at all is left.

A. No matter whether the Receiver be wholly, or for the greater part empty; for which ever you suppose, the derivation of the motion from the object to the eye will be intercepted.

B. It may be so; I can't tell what to answer.

p. 51. Credin' tu, &c. Do you think these Animals were therefore so quickly killed because they wanted Air? How then do they who make a trade of Diving live under water, of whom there be some who being accustomed from their childhood have wanted Air a whole hour? No. Thatmost vehement motion by which Bladders shut therein are distended and broken, kills these Animals shut up in the Receiver.

Ibid. Ego contra, &c. I on the contrary think that neither the Air can be suck'd out, nor that the Animal would so soon dye if it were suck'd out. The action indeed to which this death is a consequent may seem either a certain suction (and so, that the Animal is kill'd by the exsuction of the included Air, its Respiration being taken away) or a compulsion of the Air from all parts towards the Centre of the spherical Glass in which the Animal is inclosed, and so may be seen to dye stifled by the [Page] tenacity of the compress'd Air, as it were, with Water; the Air more tenacious than usual, being drawn into the inwards of the Lungs, and there between the Pulmonary Artery and Vein stopping the course of the blood.

p. 53. Placet, &c. Your Hypothesis pleases me better than that of the Spring of the Air: For from its truth depends the truth of a Vacuum or a Plenum; but from the truth of that nothing follows on either part of the Question. The make of the Air (sayes he) is like that of comprest wooll. Well; wooll is made of hairs or threds. Right; but of what figure? if of a Parallelopipedon, there can be no compression of parts: if not of a Parallelopipedon, there will be betwixt the hairs certain spaces left, which if they be empty they suppose some place empty, to prove that a Vacuum is possible; if full, they say that is full which they suppose to be empty.

p. 56. Fuere, &c. There were some of them that said there remained in those coals (though they seem'd extinguish'd) some fiery Particles, which being blow'd up by the Air upon its admission did re-kindle the rest of the mass.

Ibid. Nae, &c. In good faith they seem not so much as to have considered what they should speak, as to have taken it up at all adventures. Do you believe that in a kindled coal, there is any part which is not a coal but fire; or in a red-hot Iron there is any part that is not Iron but Fire? A great City may be set on fire by one spark: Now if the body of fire be different from the thing fired, there can be no more parts of fire in the whole Town on fire than that one spark. We see bodies of divers kinds may be set on fire by the light of the Sun, as well by the Refraction as the Reflexion that is made in Burning-glasses. And yet I do not believe that there is any man thinks that Particles of fire darted from the Sun can pass through the substance of a crystal Globe. And in the Air between the Sun and the Globe there is no fire.

p. 58. When is it that we may truly say of a man that he is dead, or (which is the same) hath expired his Soul? For it has been known that some men who have been taken for dead, being brought out the next day revived.

A. It is hard to determine the point of time in which the soul is separated from the body. Proceed therefore to other Experiments.

p. 59. Si acus, &c. If a Needle excited by a Loadstone hang freely within the Receiver, it will nevertheless follow the motion of the Iron which is drawn about without the Receiver. So objects put within will be seen by those that are without, and sounds made within will be heard [Page] without: all these as well after as before the exsuction of the Air, except that the sounds are somewhat more weakly heard after than before.

B. These are most manifest signs that the Receiver is alwayes full, and that the Air cannot thence be suck'd out. That the sounds thence are more weak to ones hearing is a sign of the consistence of the Air; for the consistence of the Air is diametrically opposite from its motion.

p. 61. Quia nihil &c. Because there was nothing there that the weight of the Atmosphere should do; no more strong or evident Argument could be made against a Vacuum than this Experiment. For if of two coherent Marbles either of them should be thrust forward that way that their surfaces lye contiguous, they would easily be sever'd; the neighbouring Air successively flowing into the deserted place. But so to pull them asunder, that at one time they should lose their whole contact, is impossible, the world being full. For then either motion must be made from one term to another in an instant, or two bodies at the same time must be in the same place: to say either of which is absurd.

p. 62. Confitentur, &c. They themselves and all others confess, that all Ponderation is an endeavour every way by right lines unto the Centre of the Earth; and so that it is made not by the figure of a Cylinder or Column, but by a Pyramide, whose top is the Centre of the Earth, and whose Basis is part of the surface of the Atmosphere.

Ibid. Conatus, &c. Therefore the endeavour of all the points that ponderate will be propagated to the surface of the upper Marble, before it can be propagated further (suppose) to the Earth.

p. 64. Has, &c. These Scales he puts one upon another and draws out the Air, and then are they kept so comprest and united by the gravity of the external Air, that six strong men cannot pull them asunder. But if at length by the use of utmost endeavour they are pluckt in sunder, they make a noise equal to the report of a Musquet; but as soon as ever by the Stop-cock open'd there is the least entrance given to the Air, they are severed of their own accord.

p. 65. Sed vis, &c. But can the Spring, which they say is in the Air, confer nothing to the holding up the Marble? — Nothing at all: For there is no endeavour of the Air to the Centre of the Earth, more than to any other point in the Universe. For seeing that heavy things tend from the circumference of the Atmosphere unto the Centre of the Earth, and thence again to the circumference of the Atmosphere by the same reflected lines, the endeavour upwards will be equal to the endeavour downwards, and so destroying one another they will endeavour neither way.

[Page]p. 66. Non potest ergo pars BC, &c. Therefore the part BC (that is a part of the Atmosphere placed any where within the whole) cannot (by reason of its greatness) descend, although it be heavy, and therefore it cannot press or gravitate.

Ibid. Si possibile, &c. If I should deny it possible, that by the art of man two furfaces of two bodies could be made so accurately fit that they should touch in all points, so that there could no creable Corpuscle pass between them; I do not see how they could defend their own Hypothesis, or disprove our Negative assertion.

Ibid. Vtraque, &c. Both these Fancies, as well that of the Weight as of the Spring or Antitupy of the Air, are Dreams. But if it be granted that there is a kind of Recoyling in those small hairs or slender Corpuscles of which the Air consists; one may enquire whence it is that those crooked bodies, settled and at quiet in that posture, came to be moved into a streightness. They ought, if they will be esteemed Natural Phylosophers, to assign some possible cause of this.

p. 67. Cur non, &c. Why cannot the water, which when it was injected did compress the particles of Air, be again cast out by the same particles explicating themselves?

A. Because when explicated they require no greater place than when comprest: As in a vessel full of water, wherein are many Eeles, the same proportion of place receives them, whether they are folded round or at length. Therefore they cannot drive up the water by their Spring, which is nothing else but the motion of bodies explicating themselves.

B. The comparison of Air to Eeles in water I suppose will be well received by our Academians.

p. 68. Vides, &c. You see how foolish a thing it is to bring for the explication of such effects Metaphorical words, as the shunning of a Vacuum, the ahhorrence of Nature, &c. which heretofore the Schools used to defend their reputation.

Ibid. In the Gardeners Watering-pots therefore is the water suspended, because that which issues out at so small a hole is so little, that it cannot diffuse it self to such a length, that by its descent it may give passage to the Air through the circumferences of the holes. Nor can the Air driven off by the water going out find any other place besides that which the water leaves.

p. 69. Qui per, &c. He that sucks water into his mouth by a Pipe, first sucks up the Air between, whereby he removes the distended external Air, which being removed (the world being full) it can have no place but by removing the next, and so by continual pulsion the [Page] water is at length driven into the Pipe, and doth fucceed the Air which is suckt out.

p. 72. Id vero, &c. But that is impossible: For in a Siphon, unless both legs are filled with water, the water will not ascend out of the Bason. The cause of its ascent into that cloth is the motion of the earthy Atoms which are near the water, I say the simple circular motion communicated to the Air in which they move, which Atoms striking the water beat it up into the woolly matter, which beating of them against the cloth makes it more and more moist, till it becomes all over wet. And when it is so, &c.

p. 73. A. Fateris, &c. You confess then that your Collegiates have as yet in nothing advanced the knowledge of natural causes, but that one of them hath found out an Engine, in which there may be such a motion of the Air excited, that the parts of the Sphere may together every way tend unto the Centre, and that the Hypotheses of Mr. Hobbs, before probable enough, may be thence made more probable.

B. Right; I am not ashamed to confess it; for it is somewhat to arrive so far, if we can make no further progress.

A. Why so far? To what end such preparation and charge for Engines difficult to be made, to make no further discovery than Mr. Hobbs had made before you? Why did you not rather begin where he ended? Why did you not use the Principles he had laid; and when Aristotle had rightly said, That without the knowledge of Motion there is no knowledge of Nature, how durst you take such a task upon your selves?

Ibid. Est, &c.

Thus to have made an entrance though we miss

Of further progress, some performance is.

p. 75. But most of us distinguish the nature of fluid from that which is not fluid, by the greatness of the parts of which any body consists and is made up with. Wherefore we do not onely look upon Air, Water, and all Liquors, but upon Ashes also and Dust, as fluid bodies. And we deny not that fluid things may be made of things not fluid; for we do not digest the Notion of infinite Divisibility.

A. Infinite Division cannot be conceived, but (infinite) Divisibility may easily. I on the contrary do not understand the distinction of Fluids and not Fluids, which you take from the greatness of the parts: could I digest this, I must say, the ruines of shattered rubbish stones that lye in Pauls were fluid. But if those ruines cannot be called fluid because the stones are too big, define me the bigness that the parts of a ruin'd wall must have that they may be called fluid. But you that cannot understand infinite Divisibility, tell me what you think to be the cause why I [Page] should think it more hard for Almighty God to create a fluid body less than any Atom proposed, that its parts might actually flow, than to create the Ocean. Therefore you make me despair of any fruit of your meeting, by saying, that they think Air, Water, and other fluids consist of Non-fluids; as if a wall that began to fall and be ruinous were called by them a fluid body. If they may speak so, every thing is fluid, for even Marble it self may be broken into parts less than any Atom imagin'd by Epicurus.

p. 79. Ruina, &c. The ruines that lye in Pauls Church might be called fluid.

Ibid. Si sic, &c. If they may so speak, there is nothing but is fluid, for even Marble may be beaten into parts less than any Epicurean Atom.

p. 80. Divisio, &c. Division that is infinite cannot be conceived, Divisibility may easily.

p. 81, 82. Quia corpuscula, &c. But the Corpuscles (such as are the Atoms supposed by Lucretius and also by Mr. Hobbs) being hard before might be easily compacted by any of the mention'd causes, so that it is not to be doubted but that the whole to be made of those Corpuscles will be hard.

Ibid. Si dura, &c. If hard bodies are made out of parts originally hard, why are not fluid bodies made of parts originally fluid? Could great fluids, as the AEther, be created; and could not small ones? He that first made a body hard or fluid, could if he would have made it greater or less than any other proposed body. Now if a fluid body be made of parts not fluid, (as you speak) and hard bodies onely from hard parts; doth it not follow that nothing neither fluid nor hard is made of original fluids?

p. 84. B. Quaenam, &c. What are the principles of Fluidity and Firmness.

A. Of Fluidity nothing but Rest, of Firmness Motion, such as is fit to produce that effect. By Rest I understand the rest of two parts one with another, when they each touch, but neither press one another. For entire bodies of fluids may be in motion their fluidity abiding, and hard bodies be at rest although their parts be in motion.

p. 85. At (que) binc, &c. And hence it is manifest that there is a great compression in the Air so moved and shut up, namely, so great as that force by which it was driven in was able to make; and also that from so great compression some degree of consistence must be made, though less than that of the consistence of water. Now if in all the same Particles of Air, besides the motion by which one presses another, there was also [Page] the simple circular motion and that vehement enough, it would be almost impossible any one of them should be moved from its little circle; but that the other Particles resisting, the whole would be pressed together, that is, become hard: For that is hard of which no part gives place but upon the motion of the whole. You see therefore that hardness may be made in a most fluid body by this simple circular motion of Particles, which was before imparted to them by two contrary motions.

p. 86. At (que) talis, &c. And such indeed may be the cause of the Durum primum, or first hard body. But of the second, that is, of the cohesion of two of these first hard bodies, the cause may be the very same simple circular motion, conjoyned with their superficial contact, or perhaps their being one with another intricated.

Ibid. Si supponamus, &c. If we suppose with them that the cause of hardness is the greatness or thickness of the parts, what reason can we give why congealed water should be harder or firmer than the same water is before such congelation?

p. 87. Ut sit, &c. That it be conceivable, that is, not absurd; and that from its being granted the necessity of the Phaenomenon may be inferr'd.

p. 88. Qui, &c. They which putting bodies to bodies shew the new and admirable works of Nature do wonderfully inflame the minds of men with the love of Philosophy, and do not a little instigate them unto the search of Causes, and on that account are worthy of commendation.

True; for they enrich Natural History, without which Natural Science is in vain sought for.

[Page]

A Summary of the Contents of the several Chapters.

CHAP. I.

THe occasion and scope of the present Treatise. Reasons why Mr. Hobbs might have employed himself otherwise, and have spared this Discourse, p. 2. Why the Author would have been contented he had done so, ibid. Why he now undertakes the Reply, p. 3.

CHAP. II.

Of some mistakes of Mr. Hobbs touching matters of Fact and the Authors Doctrine. That he mistakes in ascribing the Explications and Experiments in the Physico-Mechanical Treatise of the Society at Gresham College, p. 3. the Experiments having been seen done long, and the book published, before the Society began, &c. p. 4. That the Experiments were not devised nor employed to prove a Vacuum, Ibid. Whether Mr. Hobbs by the Experiment of the Gardeners Watering-pot demonstrates that there can be no Vacuum, p. 5. That if the Watering-pot were tall enough, the water would run out with unstopping the upper Orifice, prov'd by M. Paschal's Experiment, p. 6. The way of Argument on both sides compared, p. 7, 8. Why the Author did not assign the cause of Springs, p. 9. That Mr. Hobbs his account of Springs is imperfect, and that he has not solved the Phaenomena of them, p. 10, 11, 12, 13. That he mistook the Authors notion of the Air, p. 14. 15.

CHAP. III.

Wherein the Weight and Spring of the Air are asserted against Mr. Hobbs. Several Experiments recited that prove the real Weight of the Air, p. 16, 17. Mr. Hobbs's Objections against the Experiment of the heaviness of a blown Bladder, p. 17, 18. answered, p. 19. The Spring of the Air asserted from Mr. Hobbs's concessions, p. 20, 21, The same asserted by particular Experiments, p. 22, 23. Mr. Hobbs his answer to that of the Bladder considered, p. 23, 24. Experiments of the Spring of the Air not comprest, p. 25.

CHAP. IV.

Wherein Mr. Hobbs his principal Explications of the Authors Phaenomena are examined. What things Mr. Hobbs takes for granted, p. 26. His Hypothesis considered of the simple circular motion, whether it be not precariously ascribed to aqueous and earthy Particles, p. 27, 28. Whether in [Page] the exhaustion of the Cylinder any Vacuum be produced, p. 29, 30, 31. Experiments to prove that the Glass is in great part devoid of common Air, p. 31, 32. Whether a purer sort of Air may unperceived dive under Water to pass into the Receiver betwixt the Cylinder and the Suker, p. 33, 34. That the Cartesian way of explicating this Phaenomenon in favour of the Plenists is more plausible than Mr. Hobbs's, p. 35. Whether the place deserted by the suspended Mercury in the Torricellian Experiment be empty or full of Air, p. 37, 38. Mr. Hobbs's Explication of that Experiment of Mr. Boyle, in which the Air impells up the Sucker together with above 100. pound weight, p. 39, 40. The Examination of this Explication, p. 41, 42.

CHAP. V.

In which divers scatter'd Explications and other passages in Mr. Hobbs's Dialogue are examined: His Explications why water without visible force ascends in a slender Pipe considered, p. 44, 45. Why the stopple of the Cover of the exhausted Receiver so much gravitates, considered, p. 46. His Explication and the Authors, why in the exhausting of the Receiver water let down into it boyles as it were or bubbles there, viewed and compared, p. 47, 48 Whether the Phaenomenon of this water bubbling in the Receiver be an evidence that there is no vacuity in the Receiver, p. 49, 50. Whether Animals in the exhausted Receiver dye for want of Air, or for the causes assigned by Mr. Hobbs, p. 51, 52. That the Author asserts not the proof of a Vacuum or Plenum to depend on the Hypothesis of the Spring of the Air, p. 53. That the Air in the exhausted Receiver is not thicker but thinner, not heavier but lighter, proved by Experiments, p. 54 55. The Epicurean Hypothesis of fire, and the effects of the Sun-beams through Burningglasses, p. 57. Whether he deserves a censure that calls kindled coals fire, p. 58.

CHAP. VI.

Wherein other passages of Mr. Hobbs's Dialogue that concern the Author are examined. That the Experiments of the Needle's motion in the exhausted Receiver, and of sounds being audible, and objects visible there, are reconcilable to the doctrine of the Atomists, p. 59. Whether from the cohesion of two Marbles the non: existence of a Vacuum follows, p. 60, 61. How the lower Marble is upheld, p. 62, 63. The power of the oblique pressure of the Air to these effects illustrated by Experiments, p. 64. Whether the throwing up of water in the Glass fountains, invented by Vincenzo Vincenti of Urbin, can be explicated by the Spring of the Air, p. 67, 68. Mr Hobbs's Explication of the cause of waters being suspended in a Gardeners Wateringpot examin'd, p. 69. An Experiment purposely devised to shew that both [Page] Vacuists and Plenists should admit an Elastical power in the Air, p. 70, 71. Mr. Hobbs's correction of the Authors discourse about the ascension of water in Siphons and Filtres animadverted, p. 72. Some unhandsom passages, and such as shew the unequal estimation Mr. Hobbs has of his own and others preformances in Philosophy, p. 73, 74. What parts of Mr. Hobbs's Treatise, and why, past by without censure by the Author, p. 75.

CHAP. VII. (Being an Appendix to the past Discourse)

Wherein is examined what Mr. Hobbs teaches concerning Fluidity and Firmness. Mr. Hobbs mistakes, and so misreports, the Authors Doctrine of the cause of Fluidity, p. 77. His Animadversions on the Doctrine considered, p. 78, 79. Whether fluid bodies are made from parts originally fluid, or from small Solids in motion, &c. p. 79, 80, 81. Mr. Hobbs's Theory of Fluidity and Firmness examined, p. 81, 82, &c. What influence therein his simple circular motion may have, considered, p. 82, 83. That there is a third requisite of a good Hypothesis, viz. That it be not inconsistent with any Truth or Phaenomenon of Nature, p. 84. That Mr Hobbs his Hypothesis wants this requisite, proved by references, p. 85. By instances out of ordinary, not elaborate, Experiments, p. 86. The Conclusion to the Reader, p. 88.

FINIS.

[Page]

A CATALOGUE Of all the PHILOSOPHICAL WORKS Published by our AUTHOR.

*NEW Physico-mechanical Experiments concerning the Weight and Spring of the Air; published in English, Anno Dom. 1660.

* A Continuation of them, Part I. 1669.

* The Defence of the New Experiments, &c. against Franciscus Linus.

The Examen of the Physical Dialogues of Thomas Hobbs, concerning the Air. These two were published, A. D. 1661.

* The Sceptical Chymist. 1661.

* Physiological Essays, together with the History of Fluidity and Firmness, and some other Tracts, Printed 1662.

* The Experimental History of Colours begun, A. 1663.

Concerning the usefulness of Experimental Philosophy; the first Tome: A. 1664.

The second Tome was Printed, 1669.

* A Tract concerning the Origin of Forms and Qualities, 1666.

Though this Tract was turned into Latine divers years before the Genevlan Collection was published, yet was omitted therein whence it appears, that the Publisher was not very cautious, who affirms in his Preface, That all Mr. Boyle's Works are contained in that Volume.

The Experimental History of Cold begun, to which is subjoined a Dissertation concerning Antiperistasis, together with an Examen of Mr. Hobbs's Doctrine about Cold; 1665.

* Hydrostatical Paradoxes; 1666.

[Page]* The Origin of Forms and Qualities; the second Edition; to which is annexed a Dissertation concerning Subordinate Forms; 1671.

* Tracts concerning the Cosmical Qualities of things; Cosmical Suspicions; the Temper of the Marine Regions; the Temper of the Subterranean Regions, and of the Bottom of the Sea: 1671.

* An Essay concerning the Origin and Vertues of Gems; 1672.

A Tract containing New Experiments between Flame and Air; together with an Hydrostatical Dissertation; 1672.

* Some Essays concerning the wonderfull Subtilty and Efficacy of Effluviums, and their determinate Nature; 1673.

Some Tracts consisting of Observations concerning the Saltness of the Sea; with a Sceptical Dialogue concerning the Nature of Cold both positive and privative; 1674.

Tracts containing some Suspicions concerning some Occult Qualities of the Air; with an Appendix touching Celestial Magnets, &c. 1674.

An Introduction to the History of particular Qualities in the Phylosophical Transactions N. 63. p. 2057.

* Of the Excellency of the Mechanical Hypothesis; N. 103. p. 53.

Experiments and Observations concerning the Mechanical Production and Origin of several particular Qualities; together with some Reflexions upon the Hypothesis of Acid and Alcaly; 1675.

The Sceptical Chymist, or Chymico-physical Doubts and Paradoxes about those Experiments, whereby vulgar Spagyrists do labour to evince, that Sal; Sulphur and Mercury are the genuine Principles of things; to which, viz. in this 2d. Edition, sundry Experiments and Considerations are subjoined concerning the Producibleness of Chymical Principles; 1680.

* A Continuation of new Physico-mechanical Experiments; the second Part; 1680.

The Aerial Noctiluca, or some New Phaenomena and a Process of a Factitious self-shining Substance; 1680.

New Experiments and Observations made upon the Icy Noctiluca, to which is annexed a Chymical Paradox; 168½.

These are the Philosophical Works of our Author hitherto published; what he hath wrote in Divinity belongs not properly to this place; not to mention several Dissertations of his which you may find here and there intersporsed among the Philosophical Transactions published in Print.

[Page]

Information about this book

Title statement

New experiments physico-mechanical, touching the airNew experiments physico-mechanical, touching the spring of the air, and its effects

Boyle, Robert, 1627-1691.

Edition statement

1682

Publication

Publisher

Text Creation Partnership,

Place of publication

Ann Arbor, MI ; Oxford (UK) :

Date

2003-01 (EEBO-TCP Phase 1).

ID [DLPS]

A29007

ID [STC]

Wing B4000_PARTIAL

ID [STC]

Wing B3942_PARTIAL

ID [STC]

ESTC R23366

ID [EEBO-CITATION]

12760915

ID [OCLC]

ocm 12760915

ID [VID]

93491

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Early English books online.

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(EEBO-TCP ; phase 1, no. A29007)

Transcribed from: (Early English Books Online ; image set 93491)

Images scanned from microfilm: (Early English books, 1641-1700 ; 707:11)

Source

— New experiments physico-mechanical, touching the air, New experiments physico-mechanical, touching the spring of the air, and its effects, Boyle, Robert, 1627-1691., Sharrock, Robert, 1630-1684., Boyle, Robert, 1627-1691. Defence of the doctrine touching the spring and weight of the air., Boyle, Robert, 1627-1691. Examen of Mr. T. Hobbes his Dialogus physicus de naturâ aëris.. The third edition : whereunto is added a defence of the author's explication of the experiments, against the objections of Franciscus Linus and, Thomas Hobbs..

Extent

[16], 203, [12], 117, [8], 102, [2] p., 2 leaves of plates (1 folded) ; 21 cm.

Printed by Miles Flesher for Richard Davis, bookseller in Oxford,. [London :: 1682]. (Title taken from half-title. Each of the three works has special t. p. and separate paging; the third has separate signatures.) (Contains the first formulation of Boyle's law.) ("A catalogue of all the philosophical works published by our author": p. [1]-[2] at end.) (Edited by Robert Sharrock.) (Reproduction of original in Huntington Library.) (New experiments physico-mechanical, touching the spring of the air, and its effects, made, for the most part, in a new pnuematical [sic] engine : written by way of letter to the Right Honorable Charles Lord Vicount of Dungarvan, eldest son to the Earl of Corke / by the Honorable Robert Boyle Esq. -- A defence of the doctrine touching the spring and weight of the air, propos'd by Mr. R. Boyle in his New physico-mechanical experiments, against the objections of Franciscus Linus : wherewith the objector's funicular hypothesis is also examin'd / by the author of those experiments -- An examen of Mr. T. Hobbs his Dialogus physicus de naturâ aëris, as far as it concerns Mr. Boyle's book of New experiments touching the spring of the air, &c. : with an appendix touching Mr. Hobbs's doctrine of fluidity and firmness / by the author of those experiments.)

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