SInce my last Opportunity of Discoursing with you, (which is now some Months past) my Thoughts have run continually upon the Subject we were then en­gag'd in, which was the Nature of Magnetism; and what with the dignity of the Matter and the Indearments of the Party who argu'd so Rationally upon it, whereof the one facilitated the remembrance of the other; I have hard­ly talk'd of any thing else waking, nay, (as I am told) sleep­ing too, and all this at last without the success that might justly have been presum'd of such frank endeavours; but that you may know how much I am the wiser, and be di­verted by my Example from lavishing too great a Portion of time upon such Gordian-knots, I have ventur'd to send you the summ of my Acquisitions. It is a Question which we know has employ'd and prov'd too hard for the Pens of the most eminent Philosophers, and is to be rank'd among those Misteries of Nature, which neither the thoughtful Ancients, the laborious School-Men, nor our acute Virtuosi, could ever make a compleat Discovery of: Not but that the Peripate­tick is verily persuaded he has seen farther into it than other People, as long as he can answer your demands with Oc­cult quality or its elder Sister Substantial form; and if this does not lay it all bare, what does? there is says he, very gravely, something whereof we cannot with confidence affirm any thing, which either within the Magnet or from without, disposes it in such and such a manner; and then [Page 2] there is another what do you call it, with which according to the Determination of its Poles, it attracts or repels a Body Congenial; and think you Sir, this answer is not very wor­thy of a Philosopher? Others have entertain'd an Opinion, that the Magnet accomplishes its Operations by the Emission of Effluviums out of its own Continuum; and this the Learn­ed have so Rationally disprov'd already, that I shall think it sufficient, if not superfluous, to offer but one Objection a­gainst it, which shall be grounded upon the Nature and Structure of the Load-stone. It is to be remembred that as that Stone is for the most part fetch'd out of Iron-mines and foster'd in Beds of Iron Ore; so in its Nature it scarce varies from that Metal, save in the eminence of one Quality which is Compactedness; for altho' in other Qualities it dissents from Iron, as in its Gravity, Inductility, and Microporosity or littleness of Pores, yet in these it rather differs from the Me­tal consequentially than essentially, since the Original and Fountain of them seems to be the Quality of Compactedness, for the comprehension of more univocal matter in less Space, which is but a Periphrasis of Compactedness unecesarily re­quir'd to gravity; and then as for its Inductility, 'tis con­fessed that the most compact and heavy of all known Bodies which is Gold, is the most Ductile and Malleable, but it is not reasonable to conclude from thence, That the most Ductile and Malleable Bodies are always the most compact and pon­derous; Ductility or Malleableness as I conceive, requir­ing no more than that the Parts should be of such a Figure as would be least impatient of those Impressions, suppose of an Aequilateral Quadrangular Superficies, whereas such a si­militude and correspondency of Parts seems not to be abso­lutely necessary to a Bodies becoming heavy and compact, so their Connexion and Union be but such as admits of the smallest Interstices and Pores; not but a coincident Figure of Parts, such as that I just mentioned an Aequilateral Quad­rangular, contributes much to Compactedness, for which reason all Architects take care their Materials be of such a form. But the parts of the Load-stone are in all probability so far from Aequilateral-Quadrangulars, that they are rather to be supposed of a Branchy stragling Figure as the Parts of [Page 3] Iron, yet because those Branches are better and closer Plait­ed and Connected one with the other than those of Iron, which are so loosly dispos'd as to be even thorough fares for Heterogeneous Matter, they become more Inviolable and Inflexible than those of the latter; nor is there any far­ther occasion to prove as much of the Tenuity of its Pores. seeing therefore the Magnet and Iron have so near an Affini­ty as to be in respect of Magnetism, two Species of the same Genus, and their difference chiefly to consist in the Dignity and Degrees of some Accidents, on account of which Iron may be reputed an imperfect and Bastard Load stone, and the Load-stone the most pure and noble Iron; there will be found but few Phaenomena which may not be attributed to both indifferently, wherefore it ought to be a general Pro­legomenon in disputes upon this Subject, That Magnetism, not of the Magnet only properly so called, but of all Mag­netical Bodies is the Theme. Magnetical Bodies being therefore naturaly unapt for Malleableness and Ductility, though one Species less so than another; it will follow that notwithstanding they are tight and compact, yet that the Parts of them are of no Quadrangular regular shape, but on the contrary of a stragling Branchy one, though strongly Interwoven and Connected; whence it is Demonstrative that the Effluviums of Magnetical Bodies flow not from with­in themselves, for by such a Procession and Expiration, it is certain there must be a very considerable and visible ex­pence of the Parts: for though slightly considering the mat­ter, it may be answered that the Evaporating Particles are few and slender, yet when their mutual Dependence and Concatenation is weigh'd, it will appear that one single Par­ticle cannot escape without the attendance of its whole Chain, so that in a short time there would necessarily suc­ceed a very sensible and obvious decay of Parts; and this may suffice you for the Confutation of the Opinion of Perspiration. I shall not worry you with the rest of those Hypo­theses and Notions which some Mens Brains have teem'd­with; such as the Influence of the Stars, or the entire Mag­netism of the Earth and the like, which instead of giving a light into the Question, is but meer building new Extra­vagancies [Page 4] and Errors upon our Antecedent Ignorance. I have therefore only a Word to say to Des Cartes and the Materia Pennata Men, and so shall go on to perform my promise. The latter of them seem to be offenders against all Reason and Rule too; it is a receiv'd Maxim or Postula­tum among Philosophers, That Entities without a necessity are not to be Multiply'd, and if so, then certainly are those Philosohers to blame, who have invented a new Species of Matter, of an unaccountable extract and production to ef­fect those Operations which another Species of Matter, the existence whereof is evidently known has Power to effect. But as for the Ingenious Des Cartes, it were an unpardona­ble peice of Ignorance and Envy, not to acknowledg his Hypothesis to be the most satisfactory and adequate Account hitherto Published; but yet as a Man's having good Eyes when he walks in the Dark, will not save him from stum­bling some times, so neither could the Perspicacity of this great Man, ensure him from many mistakes in the trace of so profound a Secret. For not to mention to one who knows them so well, the many perplexities which the Learn­ed have discover'd in his Philosophical Principles, altho' the reality of his Magnetical System must unavoidably stand or fall with those Principles: I say not to mention any thing of this; there are yet some difficulties observable in the Sy­stem it self; take one for all, for his Instruments, he sup­poses a sort of fine Matter to issue out of both Poles of the Earth after such a manner, that those that come from one Pole take a compass round the Superficies of the Earth and enter in again at t' other, which matter he has Denominat­ed Corpuscula Striata, because of the Strias impressed upon it by being drain'd thro' the Apertures or Interstices necessarily left-between the contacts of the Globuli of his second Ele­ment; This matter he supposes to be a Species of his first Element, which he defines thus, Quoe tantam vim habet agita­tionis, ut aliis Corporibus occurrendo in minutias indefinitae parvita­tis dividatur, & figur as suas ad omnes Angulorum, abijs relictorum angustias implendas, accommodet; It is, says he, so agil a kind of Matter as upon encountring other Bodies, to dash into innumerable Particles, and conforms it self to the Spaces [Page 5] which are left between those Bodies. but how is it possible to conceive, That Matter of so easy and yeilding a Nature should not be as Susceptive of an Impression from, and as conformable to the Pores of Bodies compounded of third Elementary Matter, in the number of which are Magneti­cal Bodies, as it is to the Interstices of the Globuli of the se­cond Element, which if it be, then cannot it act with any force or impulse, but must glide ineffectualy thro' the Pas­sages of the Magnet, and like a winding Stream comply with the Luxuriancy of its Channel; nor will it avail to say that this Matter upon approaching the Poles of the Magne­tical Body is Congregated, and Acts with an united force, since we cannot see why it should more readily congregate and confederate upon such an accession than before or after it, unless, which this Learned Philosopher I am sure will not admit, it is Collected by some Sympathetical Attraction of the Magnetical Body. thus Sir, you see one Difficulty, and were it needful perhaps I could make you sensible of many more; but I am unwilling to attempt a Dispute, which would be as endless as the Ropings of the Welchman's Toasted Cheese. Now be pleased to hear what I can say for my self.

It is apparent that there can be no such thing as Motion without an Impulse, and that upon such an impulse a Mo­tion greater or less must ensue; from whence we gather that all Magnetical Bodies require some Impellent to enable them to perform those various Feats and Operations obser­vable in them; and here an Inquiry will arise, were we shall meet with an Agent confessedly existent in Nature, neither too gross not too feeble, but in all respects qualify'd for such undertakings, Corpuscula Striata or Pennata, as has been al­ready shewn, are Fabulous or Impotent if not both, and the daily Testimonies of Mens Eyes assure them that no visible Conspicuous Agent is in the Cause; of necessity therefore it must be something of a midling kind between these two, which cannot be any other than the Aethereal or Subtile Matter incorporated in the Atmosphere of our Terraqueous Globe, which Matter by the diurnal Motion of the Earth is rapidly devolv'd from West to East perpetualy: Now you [Page 6] will presently wonder, I do not doubt, how that which moves from West to East should direct any Magnetical Body so as that its Poles should point directly North and South, but have a little Patience. The existence of such Aethereal Matter I am confident you will not call in Question, and that it is endu'd with a Scrutinous penetrating Nature may, were it not trivial, be Demonstrated from the very end and essence of it; but still this Agent suffers under the Imputa­tion of Insufficiency and Variability equally with that of Des Cartes, and considered by it self undoubtedly it does so, but considered with Circumstances as the Precipitance of its Motion, the Disposition of the Parts of its Patient and the like, it will answer your Expectation and Demands. Thus the Wind can manage the Sails of a Windmil, and turn them round with ease, but has no Power upon a Rock or a Mountain; from hence it is evident therefore that this Agent must be driven with a due force of Motion, and al­so that the Patient must have some of its Parts adapted for receiving and suffering the Impulse. Whoever takes a just estimate of the Earths Celerity in her diurnal Motion, must be convinced that the Violence of such a Motion is able to effect great things, and whoever remembers that the Motion of the Aethereal Matter about the Earths Superficies must be proportionably quicker as that is Degrees fluider, must also be satisfy'd of the abilities of such Matter to penetrate all the accessible passages of those Bodies, which occur in its course and to rage and aestuate in them, if they be not very regu­lar and open.

Having thus obtain'd an Agent; there are two things next to be examin'd, the one is whether this Agent when it is free and uninterrupted is capable of such an Administration; The second is, Whether though it be so of its self, yet ex­ternal Diversions and Disturbances may not frustrate and evacuate its Influence, which Queries being both Answer­ed, I hope no further difficulties will remain. In order to clear the first, I must give you to understand that many of the Particles of Magnetical Bodies are like so many Tend­rils or little Springs, Taper and Tortuous, which in regard of the Internal Disposition and Posture of Magnetical Bodies, [Page 7] and the many anomalous Ramosities into which the Parts of them spread themselves, I may expect to be easily grant­ed. The Body of the Aethereal Matter therefore rushing into the Pores of the Magnetical Bodies, and there labouring to exert its self on all sides, and obtain a free Passage or a convenient Receptacle, distends and explicates these little Springs which lie ranged in one and the same order, from this Pole to that Pole of the Magnetical Body, the conse­quence of which distention can not be a direct Progressive Motion of the Body, because then all parts of these Springs must equally resist the Impulses of the Aethereal Matter, but being of a Taper form, larger and stronger toward the Radix of them than toward their Summity or Cuspis, (for­give my Pedantry where I cannot help it,) the finer and weaker parts of them suffer a readier or more forcible Ex­pansion or Diastole than the larger and radical, whereup­on ensues insted of a Progressive Motion a Deflexion or Distortion of the Springs themselves, and of the Continu­um to which they adhere. For instance, If the Radix of the Spring of a Watch were fastened to a peice of Wood or Iron, when the Summity or lesser Parts of that Spring were distended and display'd, it would not carry the Wood or Iron at the end of it in a direct Motion to any Point just before it, but it would turn and move it round within the Limits of the same Area, on which it lay before the Terminating weaker Parts were expanded; and this Distention may very easily be effected by the Vehemency and Agitation of the Aethereal Matter, which (to make a gross Comparison) Acts as vigorously upon them as the Wind in a crop of Corn, or among the sprigs of Trees. When therefore the Poles of Magnetical Bodies are thus deflected to the Points of North and South, the equal urgency of the Influx of the accessory Aethereal Matter upon all Parts of the Magnetical Body, de­stroys the Strength of the Impression, and stays its Motion at just that Instant; for it must be remembred that the sides of the Magnet have not Pores fit to receive the Aethereal Matter, which therefore upon impaction flows round it in a Vortical manner, as shall be better explain'd hereafter. So the first dificulty disappears, the second follows, Whe­ther [Page 8] though our Agent be capacitated, yet external Diver­sions and Disturbances may not frustrate its Influence. The Cartesians I hope will not be the Men that start this Quere, their Doctrine of the Loadstone labouring under the same or a worse disadvantage; for if external Commotions as of the Wind, &c. can confound the order and irritate the Operation of our Aethereal Matter, whose Motion is so certain, regular, strong and unintermitted; what will be­come of their Corpuscula Striata or Pennata, they being not only obnoxious to accidental Ruffles and Perturbations, but continually thwarted and Transverst by this flux of our Sub­tile Matter? But I am persuaded we are both out of dan­ger from Storms of every kind, and need not shrink at the rage of Whirlwinds and Hurricans, for such is the minute­ness and velocity of our Agents that they make their way thro' all Opposition: like an Arrow in the Aire, or a good Keel through the Waves, or as the Sunbeams directly dart thro' the Atmosphere many times when 'tis vext and tost with the Winds; which last Similitude carries the most in it, on account of the vicinity between the matter of the Sunbeams and our Subtile or Aethereal Matter; And thus we are past the two Impregnable Wards of this Inchanted Labyrinth.

You will look perhaps that I should examine all the in­stances and Energies of Magnetical Bodies, and should solve every particular Phaenomenon by this Hypothesis, but if you do you will be deceived, for I am not yet so prodigal of my Time or of my Paper, which of late is very considera­bly risen, as I suppose you have e're this experienced, and therefore am of Opinion that the explication of these Five Properties following may suffice.

First, the Magnet (for now we come to particular cases) if it be unrestrain'd and have its just Liberty, will turn about till its North Pole directly answers the South Pole of the Earth, and its South Pole the North Pole of the Earth: Of which conversion I need not repeat to you the cause, hav­ing already so lately and largely spoke of it.

Secondly, If two Magnets lye at a convenient distance one from the other, and their Poles be disposed for their Accession, as when the North Pole of the one faces the [Page 9] South Pole of the other, or the South Pole of the one faces the North Pole of the other, they will close, and if their Poles are laid just contrary wise they mutually retreat, for you must know the Aethereal Matter which effects to move in a Mathematicaly Circular Line, upon invading the sides of the Magnet, finding few or no Pores to receive it, the main course or grain of the Pores lying extended from Pole to Pole, deviates from its regular Line of Motion and flowing round all parts of the Magnets Superficies, falls into a kind of Vortex on all sides of the inclosed Body; when therefore two Magnets are situate at such a distance off each other that the intermediate Space is too close and narrow to Transmit the influxes of so much of the Aethereal Matter as is carried round the approximated Poles of both Magnet's, the Influxes unite and generate one Vortex common to them both, which cannot come to pass but at the same time the devia­tion of the Aethereal Matter from its regulare line of Mo­tion will encrease, and consequently with it its Propensity to recover it again, whereupon must ensue a stronger Im­pression and Protrusion than ever upon the exteriour Poles of both Magnets, they being the Points of its widest devia­tion, and to their Impression the Magnets giving way imme­diatly close, so that the nearer they lie to one another, the stronger is the Impression upon their exteriour Poles, the weaker the resistance of the Interposing Matter, the fud­dainer their Concourse, and the firmer their Unition, & vice versâ. The requisiteness of their Dinominal Poles facing one another is plain, because that Position which is natural to them, separately consider'd, cannot but be the most suitable for their Unition; and the reason of their flying one another when their Cognomininal Poles are Approxi­mated is this. The Central Parts of the Vorticle wherein both Magnets are immers'd, conform as in all Vortexes whatsoever to the Motion of the exteriour Parts, and that is as we have just observ'd, a Deviation or Distraction or equal Division of the Vortex it self toward either Point North or South, and such by consequence must the distri­bution be of the Central Parts of the Vortex, and therefore acting with equal strength on both sides, if those of one [Page 10] side, that is toward the Polar parts of the Magnet, on one side meet with so disagreable a Texture of Parts, as obliges them to retire unsuccesful, and those which act on the o­ther side or toward the Polar parts of the opposite Magnet are more mildly received, as it will be when their Denomi­nal Poles are placed over against one another, this would be apt to drive away one of the Magnets from the other, were not the Impression of the external Parts of the same com­mon Vorticle more powerful than that of such Central Parts; but when the Cognominal Poles of both Magnets face each other, the Impression of the Central Parts of the Vortex on both sides will be equal, and their mutual renitency will as easily overpower the Impression of the external Parts of the Vortex, as a Man that should be to bend the Body of a young Tree, though with one Hand singly he were not able to move it, yet when he set his other Hand against the Body of another Tree of equal growth, would find it in his power to bend them both. The following Draught will Illustrate this.

Thirdly, If two Magnets be duly dispos'd, one will support and sustain the other in the Air, as also a Magnet will in like manner sustain a peice of Iron, which is very easily accounted for, the second Phaenomenon being well understood, for being first united in the manner there describ'd, their Cohaesion [Page 11] must be as valid and tenacious by reason of the pressure of the Aethereal Matter upon their Superficies, as is the Cohae­sion of two Polished Marbles thro' the compression of the External Air; and the same is to be said of Iron, which as was hinted before to you, seems to be but a Bastard Load­stone.

Fourthly, A Loadstone will Communicate its Faculties and Affections to Iron: for you are to remember that Iron is of a Congenial Nature with the Magnet it self, and that therefore it requires but a little Modification to render it compleatly Magnetical, which Modification it under goes from the Loadstone as it lies in its proper posture, for altho' the Loadstone does not then abound with or discharge the Aethereal Matter in such Plenty as when it is laid with it Poles East, and West, yet a more moderate Concoction and Ebullition of the same kind of Matter continues, which Con­coction being effected among the Springs of the Magnet, the Aethereal Matter which is agitated and Concocted must of necessity receive such a peculiarity of Motion as the Pas­sages lying among and between those Springs will Model it into, and issuing out of the Magnets Poles in such a Motion it enters the Pores of the Applicated Iron, where finding at once a larger Liberty (the Pores of Iron being more lax than those of the Magnet) and also new Recruits of other Aethe­real Matter, which enters the large Pores of Iron at all parts of it alike till such Iron is Magneticis'd, it aestuates with great­er vigour, joins forces with the Aethereal Matter that it finds in the Iron, Communicates to it the same Species of Motion, and both in Conjunction, Purge, Polish, Frame, and in all respects prepare those Particles of the Iron which are capa­ble of being wrought into Magnetical Springs, and when by such a course they are wrought into those Springs, the Iron becomes compleatly Magnetical; for as the Coadjution of the Cock is required toward the Perfectionating those Se­minal Principles the matter whereof rests in the Ovary of the Hen, and without such Coadjution would prove at best A­bortive: so there appears a necessity of the Irons receiving the influx of the Aethereal Matter, which was Model'd in the Magnet, to beget such a Motion of its own Aethereal Matter [Page 12] as might compleat its Magnetism, which Analogy I think fairly explains the whole Supposition.

Fifthly, Magnetical Bodies are divested of their Qualities either by Rust or Excandefaction, or if they are confin'd any length of time to a forc'd and violent Position: The first partly Corroding, partly Distempering, and partly In­cumbering the little Springs; the second utterly destroying them, and the third suffering Malignant and Heterogeneous Matter to disturb and Choak them.

So much good Friend, for our Physical consideration of Magnetical Bodies, for I am very loath to examine all those other Phaenomena, which patienter Naturalists in better times have enumerated, especially since those already discussed are the most difficultly solv'd of any of them. If you are angry to see coarse Fare garnished with such variety of hard Words, which I must confess is a fault much in vogue among our Philosophers, and after all is no more than a Vacuum Disseminatum in their Books, I must e'n tell you I could not help it; Delicacy of Subject and Newness of Notion (such as it is) would have it so; nor can I take offence if my Opinion in a Matter where­of many have wrote much to little purpose, merit not your Approbation. To feed my imagination with hopes of success after the disappointments of such Heroes of Phi­losophy, were as Sawcy and Presumptious, as it would have been in one of Hercules's Wives to pretend to beat her Husband after he had Conquered his twelve Labours; nay, so little do I promise my self of any thing like it, that I am very apt to believe all our Inquiries into the Causes of Magnetical Operations are next to desperate, and will ever be so. Indeed the All-wise Authour of Na­ture seems to have design'd them not so much Objects of our Curiosity, as matter of our Admiration, and I might add of our Imitation; for where is there that Emblem or Hieroglyphick which in so lively Colours represents the Pas­sions and Morals of Mankind? The Malicious and Quarel­some World see themselves Mock'd while they behold two Stones fly on another for no other Reason than an innate Natural Aversation. again the Covetous may blush to see [Page 13] in the manner of the Magnet's Communication the Picture of one at Home, who instead of spending any part of his Treasure upon himself, spends himself wholly upon that. again it's perpetual Affection of the same Points of the He­misphere, exposes the Ambitious and Voluptuous, whose Souls are so link'd to Greatness and Pleasure, that they seem to have forfeited the Priviledge of a free Will. On the other Hand it tacitly teaches Rational and Sober Men the necessity of directing their Designs and Actions all to one end, and in Order thereto of preserving a mutual Un­animity amongst themselves. As therefore the Magnet seems primarily, and especially to be deputed to this Mo­ral use, for in the whole Republick of Nature, there is not an inanimate Body more edifying, nor certainly an animate more inscrutable, so does it discharge this function in a manner most punctual and at the same time most unintel­ligible. and in this Instance as in many others, the Com­modiousness and Utility of the Phaenomena compensate for their Latency and Obscurity; for as for those artificial Pur­poses we have taught it to serve, particularly in Navigation, they do not appear to have been the Genuin and Natural ends of it they being altogether Precarious and Contingent; so that the study of its Instructions is much more safe and benificial than the study of its Construction▪ and did Philoso­phers observe this Rule in all their Philosophical enquiries, it would make much more for the credit of their Profession, and be of greater advantage to Mankind in general; we should have less of their Errors and more of their Reason; and that Science which has lost its Reputation by its Falla­cies and Presumptions, would by these means more than recover it; nay, doubtless a clear Knowledg of the true uses of things, would give us a better Light into the Na­ture of them, then their Nature gives us into the uses of them. But I decline the Prosecution of this Argument as hav­ing been so Particularly and Elegantly manag'd in the Case before you, by a learned Gentleman of the last Age; this only I will add, That whether any or all our Disquisi­tions of this kind succeed or fail, we shall have still new Motives of expressing our Praise and Veneration to the Al­mighty [Page 14] Lord of all things; our Praise when they succed for his having permitted the Children of Men to know so much of the Methods of his Providence, and our Veneration where they fail. For who can do other than adore and revere the infinite Power and Wisdom of the Creator, When the noblest of humane Faculties are not able with the nicest Inspection to make any satisfactory discovery of the Frame and Constitution of the Creature. Let therefore that Orizon with which we lately terminated our Discourse, con­clude this Letter. That the Omnipotent Authour of all things would bestow on his Rational Creatures with their Knowledg a proportionable largess of Grace to use it to his Honour and Glory, and our own Spiritual Improvement. I hope all our Friends in the Country thrive.