AN EASY AND VERY PRACTICABLE METHOD TO ENABLE DEAF PERSONS TO HEAR: Together with A brief Account of, and some Reflections and Ob­servations upon, the several Attempts formerly made for the Benefit of such Persons.

Translated from the GERMAN OF ANDREW ELIAS BUCHNER, Professor of Medicine and Natural Philosophy in the University of HALLE.

LONDON: Printed for Mess. HAWES, CLARKE, and COLLINS, Booksellers in Paternoster-row. MDCCLXX.


THE more extensively useful, and the more adapted to the occasions of life, the matters are which an author takes upon him to lay before his readers, the more he answers that end, which every virtuous man ought, in ju­stice, to propose to himself in every address to the Public, and the more such matters claim the atten­tion and patience of the reader. These considerations have princi­pally [Page ii]weighed with me in favour of the present undertaking, and I pro­mise myself, on this occasion, the approbation of every one, who can put a due value on the enjoyment of his senses, as well as of him, who can be sensible of the great disad­vantage arising from the loss of any of them.

Sight and hearing are undoubt­edly two of the principal external senses, as they supply us with the knowledge of a far greater number of external objects, than the other senses put together; which, though indeed of considerable, are yet of a more limited usefulness, and their impairment or loss more tolerable; but blind or deaf, what melancholy objects! Both blind and deaf, what accumulated woe!

I wave, at present, the several attempts wich have been made, in order to correct the manifold defects of sight, at least to lessen or render them tolerable, confining my re­flections, on this occasion, to that of hearing; and, for that purpose I shall relate the several means de­vised, in order to amend this sense, when impaired, or retrieve it, when intirely lost; or by help of the other senses, and a tolerable degree of understanding in the patient, to render its loss, in some measure, more tolerable: And lastly, I shall select, among the several methods proposed, that, which to me ap­pears, to be the easiest and most simple. But, previous to this, I shall briefly explain the reasons of the principal defects of the sense of hearing, both from their causes, [Page iv]and from the structure of the outer and inner ear; and then more ac­curately determine the greater or less utility of the methods hitherto employed, in order to amend these defects.


CHAP. I. Containing reflections preparatory to the following discourse.

AMONG the defects, to which the sense of hearing is subject, the greatest, without dispute, is the entire loss thereof, or that, which, in a word, we call deafness. This, when ei­ther brought into the world, or contracted before a child comes to the use of his un­derstanding, and before he learns to speak, renders him very unhappy, as thereby he continues to be speechless or dumb, and [Page 2]thus precluded all social intercourse. And this is the reason, why persons born deaf, are at the same time also dumb, if not taught to speak by some peculiar devices, or by means of the other senses. To this defect of hearing, we are to class that which is called difficulty of hearing; which, besides that it comes nearest to absolute deafness, proceeds, for the most part, from the same causes, only in a less de­gree; all the other defects of this sense, as not being to our present purpose, we shall wave at this time.

All the senses have from nature their proper organs, which are in a certain de­terminate manner affected and altered by external objects; and first, in that they propagate these affections or alterations to the common sensory, and thereby render our sensations complete, and communicate them to the soul. Now, as deafness is the inability to perceive those tremulous or vibratory motions of the air, which produce sound; the cause of this defect must necessarily be, either in the organ it­self, namely the ear, or in its connection with the common sensory, the vibrations [Page 3]of the air being prevented from producing the necessary and determinate alterations in those parts of the human body. The same thing holds with respect to difficulty of hearing, as being only a less degreee of deafness.

The ear consists of several distinct parts, which together concur to produce the sense of hearing. Hence, if the causes of deafness, or of a difficulty of hearing, are in the ear itself, one or more parts thereof must be injured, that is, be in a preterna­tural state. To shew this the more di­stinctly, it is necessary to consider those parts separately, and to explain the preter­natural alterations which occasion deafness, or a difficulty of hearing.

Anatomists commonly divide the parts of the ear into two sorts, namely, those which belong to the external ear, and are situate without the temporal bones; and into those that constitute the inner ear, comprising all the parts that lie within the said bones.

To the first sort belongs that which is properly called the outer ear, and the mea­tus auditorius, or auditory passage or canal, [Page 4]the inner part of which last, anatomists generally refer to the inner ear; but it may be here very commodiously treated, together with the external parts, as being only a passage from them. As the diffe­rent defects of that which is properly called the external ear, if, in other respects, the aperture of the auditory passage is not at the same time affected, may produce a diffi­culty of hearing, or other defect of this sense, but are never the causes of perfect deafness; so I shall not insist on this, but directly handle the several defects of the auditory passage, as an exter­nal part of the ear, so far as they are to my present purpose.

The use of the auditory passage is, to propagate the vibrations of the air, com­municated externally thereto, by repeated repercussions in its cavity, to the inner parts of the ear: And thence it is neces­sary, that this passage be neither obstruct­ed, nor extraordinarily constricted or straitened. In the first case, deafness is the consequence; in the last, a difficulty of hearing at least. The first defect often arises either from a long accumulated, a [Page 5]condensed, or a greatly indurated ear-wax, or from foreign bodies introduced into the auditory passage; as for instance, cherry-stones, peas, lead-shot, &c. or from tumours and imposthumes, or from fleshy or spungy excrescences therein; or, very often from the concretion of its sides from such imposthumes; or, lastly, from a pellicle or membrance growing across it, as is frequently observed in new-born children. The other defect of the audi­tory passage, namely, its too great con­striction, may arise from the very same causes, if we only except the preternatural membrane stretched across it, or the ob­struction of the auditory passage by fluid matters, which diffuse themselves on every side.

The second species of the parts of the ear, mentioned above, constitutes the in­ner ear, and comprises the membrane of the tympanum, or drum, its cavity, the la­byrinth, the tuba Eustachii, and the audi­tory nerves. The membrane of the drum receives by the auditory passage the tremulous motions or vibrations of the air, which it farther diffuses in its cavity, and [Page 6]in the labyrinth. But particularly in the drum we find four species of defects, which prevent its ordinary use: One, the too great flaccidity of its membrane, whereby it is unfitted for vibrations or tremulous motions, and so transmits sounds, either not at all, or but faintly, to the other inner parts. And hence we may judge, how it happens, that a phlegmatic constitution, moist and purulent ears, damp air, foggy and rainy weather, and the like, often increase a difficulty of hearing, to a pitch of perfect deafness. The other defect of the membrane of the drum is directly opposite to this, and consists in an extra­ordinary tension thereof; which, when to so considerable a degree, as too much to re­sist the insinuating tremulous air, and pre­vent its vibrations, gives rise in like man­ner to a difficulty of hearing, and even to perfect deafness; as may be often ob­served in the case of elderly people, and emaciated constitutions. Both these de­fects, flaccidity and tension, may also arise from an undue action of the muscles, moving the small auditory bones. But as such considerations would carry us to ana­tomical [Page 7]and philosophical niceties, we shall wave them at present, as not greatly to our purpose. The complete induration, or even ossification of the membrane of the drum, is the third defect; which may besides, from the same causes mentioned before, under the extraordinary tension of this membrane, impair the hearing. And lastly, its laceration constitutes the fourth defect, which, indeed, does not so soon vitiate the hearing; as the air, insinuating into the auditory passage, can freely pass into the inner parts of the ear, and put them in motion: but then, by this im­mediate contact, the just mentioned tender and sensible inner parts are blunted and rendered unfit for farther regular sen­sations.

The cavity of the drum, and the laby­rinth are, indeed, as consisting of bones of a more durable substance than all the parts of the ear hitherto mentioned, sometimes, however, subject to several untoward acci­dents, whereby the hearing may be inju­red or depraved. For as they are covered with a very tender and extremely sensible periosteum, which may be affected with [Page 8]inflammation and imposthume, and thereby be either destroyed, or so indurated, that no communicated vibrations of the air can any longer put them in due motion: Or, also, as these cavities are sometimes so choaked up with purulent matter, as to become unfit for propagating the vibratory motions of the air; or that at length there sometimes ensues from the imposthuma­tion of the periosteum, a caries of the bones themselves, which may intirely destroy the whole of this curious piece of mecha­nism, and unfit it for its destination.

In the last place, before I touch on the defects of the auditory nerve, I must far­ther mention the tuba Eustachii, which some reckon among the parts of the exter­nal ear, but which I refer to the internal, because the bony part of this passage lies between the temporal bone and the os multiforme; besides, the entire passage lies concealed in the cavity of the mouth: And running from the cavity of the drum to the palate, and terminating behind the tonsils, with an aperture in the mouth, is partly bony, partly cartilaginous, and partly membranous, and internally lined [Page 9]with a fine membrane full of mucose glands: This passage, I say, serves princi­pally to renew or shift the air, which is lodged in the inner cavities of the ear, in order to prevent its intire loss of elasticity by a too long confinement there. When this passage therefore is either obstructed, or intirely destroyed, the air, contained in the ear, will be unfit for the reception and propagation of that determinate degree of vibratory motion, which is necessary for the act of hearing. The obstruction of this passage often arises from a critical and catarrhous accumulation of mucus, from an incrassation and induration of this ac­cumulated mucus; from the swelling of the mucose glands; from membranous and fibrous excrescences; which, upon the erosion of the inner membrane of this passage, sometimes happen, particu­larly by a venereal taint; and from num­berless other causes. The erosion in this case happens in the same manner, as was mentioned in the erosion of the membranes of the bones of the ear.

The auditory nerve is the last, but yet a principal part of the internal ear, and [Page 10]the alone copula, or tie, by which this pe­culiar organ of sensation is connected with the common sensory. Whence also its due and regular disposition is absolute­ly necessary, in order to communicate to the soul, by means of this sense, its pro­per perceptions and sensations. This com­munication or intercourse of motion is in­terrupted, when the subtle fluid, called the nervous juice by physiological writers, is obstructed in its regular motion and passage through these nerves and their principal branches. Most pathologists reckon principally, among the causes of this interrupted passage, the obstruction of the nerve. But as from physiological principles, it does not appear, how this extraordinary subtle fluid should be incras­sated, or the fibres of the nerves drawn together or contracted; the obstruction in this case must be the same as when in the nutricious vessels, and within the involucra or sheaths of this nerve, accumulated, in­durated, or even extravasated juices from lacerated vessels, being collected, compress the nervous fibres. The principal defect, which in these nerves can possibly inter­rupt [Page 11]the motion of the nervous juice, is, secondly, their compression; which may arise either at their origin, or near the common sensory, or in their entire length, either internally or externally, by accumu­lated or even extravasated blood, or other juices of the adjacent parts; as also in the ear itself, from a caries or exostosis of its bones; which last has often been observed, particularly in venereal cases.

Besides these defects of the auditory nerve hitherto mentioned, we are princi­pally to attend to the seat of this disor­der, and to its greater or less distance from the common sensory. For, when deaf­ness arises from compression, or even ero­sion of the nerve spread over the labyrinth, there still remains a resource to supply this defect in another and that an ingenious manner; and even to produce such sensa­tions, as are otherwise communicated to the soul by the organ of hearing. But if the origin of the nerve, namely, that part thereof which lies nearest the com­mon sensory in the brain, is injured, it is not in the power of art to restore the sense of hearing. Yet by all this I would not [Page 12]on any account deny, but that dumb per­sons of this class, might by the eye, by a long, careful, and attentive observation of the different motions of the mouth in the act of speaking, be brought, at last, to understand the thoughts of those about them; as in Amman's method, of which hereafter.

CHAP. II. An account of the attempts formerly made for the relief of the deaf.

HOW various soever the causes of deafness and difficulty of hearing, hitherto mentioned, may be, many have, for a long time past, especially more lat­terly, been employed in the quest and discovery of the means of removing some way or other, or at least of diminishing this calamity. The many essays for this purpose, made by physicians and inquirers into nature, may be very properly divi­ded into two classes. To the first I refer that method, according to which, a per­son, either naturally deaf, or become so [Page 13]by some accident, may, by means of the other senses, without the intervention of the organs of hearing, or any part of them, be enabled to have those perceptions, which others obtain by the sense of hear­ing. The second class, on the contrary, comprises those methods, in which the auditory nerve itself is put in motion, and thus the very sensation produced in the soul, which we usually call hearing. This method again is twofold: One, in which the vibratory motion of sound is propaga­ted to the auditory nerve, by means of the ordinary, but, in other respects, faulty parts of the organ of hearing; by the in­tervention of some other bodies, and by a variety of ingenious devices. The other method, on the contrary, conveys sound in like manner to the auditory nerve, and thus produces the sensation of hearing, not only by means of the ordinary channels and organs, but also by means of the ad­joining firm parts of the head.

Several physicians and other learned persons have been at great pains on the discovery and improvement of the first method, in order, by the other senses, [Page 14]particularly the sight, without the inter­vention of the auditory organs, to produce in the soul the perceptions peculiar to the ear. But most of these attempts have on­ly occasionally and incidentally proved of any benefit to the hearing: As most of them have, in all their attempts, made it their principal view, to enable the deaf person to speak; though, indeed, the fre­quent and attentive observation of the mo­tions of the mouth and other parts, which concur to form articulate sounds, may give such a degree of readiness to those wretched persons, as to enable them to understand and distinguish, with extraor­dinary quickness, all the motions of a speaker, and thus also clearly to compre­hend all that is spoken. Nature herself has formed most persons uncommonly do­cile in this respect, though otherwise not endued with the brightest parts. Expe­rience very day almost shews, that deaf persons may observe by the mouth, that which others speak; and their uncommon and great attention is the reason, that they have the misfortune to be generally taken by the common people for very arch and roguish.

But this very natural device, namely by means of the nicest observation of the mo­tions of the mouth in the act of speaking, employed in order to hear, and by imitat­ing the very same motions also to speak, may be reduced to several rules, limited and de­termined by the genius of every language spoken, and thereby the learning them made much easier. This is that device, in which, for a century and a half back, many learned men have employed their thoughts; among whom Peter Pontius, Paul Bonnetus, Dr. Wallis, Holder, Sib­scota, Franciscus Mercurius Van Hel­mont, but above all others, John Conrad Amman, have most of all distinguished themselves. It would carry me too far, and be inconsistent with my present de­sign, were I to recite here all the attempts made by these learned men to this pur­pose, and their success therein. Suffice it therefore to give a short account of the latest attempt in that way, namely, that of Dr. Amman; and at the same time to point out its principal defect; but as to the others, briefly only to mention their writings, or other accounts we have of [Page 16]them. Peter Pontius, a Spanish Bene­dictine, who lived towards the close of the sixteenth century, made the first essay in this way, and taught deaf persons both to write and to speak. His method, which he did not himself describe, was afterwards improved by Paul Bonnetus, a master-gunner of the king of Arragon, and explained in a particular writing, en­titled, Reduccion de las letras, y arte para ensenar hablar los mudos; i. e. The re­solution of the letters, with the art of ena­bling dumb persons to speak, Madrid, 1620, in 4to. Dr. John Wallis, who af­ter both the former applied himself to improve this art, gave a description there­of, both in his Tractatus grammatico-phy­sicus de loquela, and in his letter to the honourable Mr. Boyle, de surdis mutis (que) informandis. The former tract is also pre­fixed to his Grammatica linguae Angli­canae, published in 1653, and was after­wards often published with Dr. Amman's writing. But the latter we have in the philosophical transactions, No. 41; as also in the Ephemerides acad. nat. curiosor, Dec. 1. Ann. 1, in append. p. 11. & seqq. [Page 17]About the same time Dr. Holder, subdean of the king's chapel, published in 1669, in 8vo, a book, called Elements of speech, &c. together with the art of teaching deaf and dumb persons to speak. In the year immediately following, namely 1670, George Sibsesta published, also at London, the following book, namely, Deaf and dumb man's discourse, or concerning those who are born deaf and dumb; to which he subjoined a treatise, De ratione loquelae cre­aturarum animatarum. Lastly, the youn­ger Van Helmont attempted to explain more distinctly, the natural formation of the letters of the alphabet, for the bene­fit of the deaf and dumb; but the has confined himself to the Hebrew language, and given his rules in his Alphabetum na­turale Hebraicum, which has been several times reprinted: I have seen an abstract of it under the following title, Francisci Mercurii ab Helmont alphabeti verè naturalis brevissima delineatio, quae simul methodum suppeditat, juxta quam, qui surdi nati sunt, six informari possunt, ut non alios solum lo­quentes intelligant, sed et ipsi ad sermonis [Page 16] [...] [Page 17] [...] [Page 18]usum perveniant, Ann. 1667, in 12mo, cum fig.

But above all others, John Conrad Amman, a physician of Amsterdam, dis­tinguished himself more, towards the end of the last century, by his ingenious method of teaching the deaf and dumb to speak: And after having happily succeeded in his method, not only on a deaf and dumb girl at Harlem, but also on his own daughter, and on several others, he published, in 1692, at Amsterdam, his Tract of Surdus loquens, in 8vo, wherein he laid open the whole of his method. Which being afterwards published in English by Daniel Foot, and highly ap­proved by the learned, he gave a new and more enlarged edition of it at Amster­dam in 1700, in 8vo, under this title, Dissertatio de loquela, qua non solum vox humana et loquendi artificium, ex originibus suis eruuntur, sed et traduntur media, quibus ii, qui ab incunabulis, surdi et muti fuerunt, loquelam adipisci, qui (que) difficulter loquuntur, vitia sua emendare possint. And afterwards there came out several editions thereof, a proof of the good reception it met with [Page 19]from the public. On this foundation William Kerger established his method in his epistle De surdo-mutorum cura, published in the appendix to the Ephe­merid. Acad. nat. curiosor. Cent. I. & II. p. 233. seqq. accommodating his instruc­tions to the German language, together with a succinct account of his predecessors in the same method of treatment.

The whole of this method rests on that well known physiological principle, in­contestably confirmed by daily experience, namely, that we communicate our thoughts to each other by means of articulate sounds, formed by the organs of speech, which we call language: And, by a daily prac­tice, we insensibly learn to form with every conception, a certain articulate found. The simple articulate sounds are generally four and twenty, and in several languages fewer, called letters of the al­phabet; which, when combined according to certain rules, and pronounced at once like a single articulate sound, are called syllables, and a farther combination forms that which we call words. But all these articulate sounds, in order to their pro­duction, require, at the same time, a cer­tain [Page 20]visible alteration and motion in the organs of speech, namely, the lips, teeth, tongue, cheeks, larynx, &c. For in­stance, all sounds, articulated by a bare aperture of the mouth in different degrees, are called vowels: And all others, form­ed by means of the other parts, are mutes or consonants. And, indeed, the accurate attention to, and careful imita­tion of, all the particular motions requi­site to the articulation of sounds, consti­tute the whole of Amman's method.

As in this, or in any other method of the same kind, the organs of hearing contribute nothing to the effect, it may indeed, be employed in all the defects and imperfections of the auditory organs, by which either deafness or a difficulty of hearing is produced. This method, however, is subject to several considera­ble imperfections, which render it greatly inferior to some of the following methods, by which the auditory nerve itself is at the same time made to be affected. In the first place, let us suppose a case, and which actually happens, as appears from the history of diseases, namely, that such a persom is born deaf, dumb, and blind. [Page 21]No one, certainly, though more dexterous than Amman himself, could, by that me­thod, impart the conceptions, which, in other respects, arise from the sense of hearing. But then it may be alledged, that if he cannot see, he may feel, at least. I grant, that he may learn to speak in that manner: But then, for one in this condi­tion, to lay his hands on the mouth and throat of the speaker, would appeal clum­sy and aukward: Not to mention, that in forming sounds, several motions are performed with the tongue, the teeth, the cheeks, the gums, &c. mostly observable by the eye, but not properly to be felt, without interrupting the speaker at the same time.

The second imperfection in this method, consists principally in confining the con­ceptions imparted, barely to language. All those ravishing sensations, which, in other respects, the sense of hearing is sus­ceptible of, are here quite lost; nor can the thrilling motions of the organs of speech, instantaneously lost in each other, when raised with that rapidity in the ex­pressions of the deeper Passions, as to [Page 22]strike and surprize the hearers, be once distinguished by, much less yield, that melting sensation to a person so wretched. Much less could a skilful musician throw him into those soft and calm raptures, when under his hands, the strings, in har­mony truly divine, thrill the hearer with unspeakable delight. Thirdly and lastly, take a person of little or no natural abilities, and attempt to teach him in this manner; I am fully persuaded, that all the pains taken with him, would be quite lost: Not Amman himself, with all his art and practical skill, could hope to succeed in a case of such indocility.

I now proceed to the second order of the attempts made to restore hearing to the deaf, by putting the auditory nerve itself in motion, thereby producing the sensation of hearing. I have already shewn above, that this order may be pro­perly divided into two sorts. To the first belong the methods of propagating sound in a due degree of motion, by the ordinary though faulty organs of hearing, quite to the auditory nerve. To this we may justly refer all those contrivances, which, either [Page 23]by peculiar instruments, or other means or devices, raise or heighten the moti­ons and repercusions of the air in the chan­nels and cavities of the ear; when those parts are so faulty as not to be put into the proper vibratory motions by the ordinary action of sound. And in this case it is al­ways requisite, that the auditory channel be open.

When the auditory channel is thus open, or the other parts of the inner ear connec­ted therewith are susceptible of some, though a very faint degree of, vibratory motion, and only require a greater ac­tion of the insinuating air than is necessary in a natural state, there hence arises a dif­ficulty of hearing, and not a perfect de­gree of deafness. Now as among the se­veral methods of propagating sound, by means of the parts mentioned, to the au­ditory nerve, in natural order, they are only of service in difficulty of hearing, but not in the case of perfect deafness; I shall therefore mention only, in brief, some of the means of this species of method. And one of the best known, and which nature herself, for the most [Page 24]part, points out, is, to apply the hand bent and hollow to the ear, and there­by not only to convey a greater quan­tity of vibrating air to the auditory chan­nel, but likewise to raise or heighten its repercussions. With this view al­so, such persons generally set the mouth wide open, when they want to hear more accurately; that the air, reflected from the palate, may be forced through the tuba Eustachii into the cavity of the drum, and thereby render more intense the vi­bration of the air. But then we are to suppose this last mentioned channel to have no obstruction.

And this very heightening the action of sound, is procured by means of peculiar instruments. Of this sort are acoustic trumpets or horns, instruments commonly well known, and which require no parti­cular notice to be taken of them here. Somewhat less known is the ingenious acoustic drum of Father Sebastian Truchel, a Carmelite monk, which, in 1718, he presented to the royal academy of sciences at Paris, and which had their approbation. This drum consists of gold-beater's skin, [Page 25]which is originally ox gut. This skin is stretched either on a round or an oval hoop, as is commonly done in drums; so that when fastened to the ear, it forms, with the natural membrane of the drum of the ear, a perfect drum; the artificial skin exhibiting the part which is struck upon; the ear itself again and the auditory chan­nel, the kettle or hollow cavity of the drum; and the natural membrane of the drum of the ear, the undermost skin of the drum. The artificial skin had, be­fides, over it, a raised cover, in shape of a box, whose aperture was turned to the mouth of the speaker. A person hard of hearing in both ears, may, by means of a semicircle of brass or silver, which goes round the hinder part of the head, under the hair or peruke, fasten two such drums to his ears.

We are now at length come to the other method of the second class or order, comprising those means which convey found, and thereby restore actual hearing by extraordinary ways, and not by means of the natural auditory channel, to the auditory nerve. But before I explain the [Page 26]peculiar methods under this head, I must here borrow three prepositions as princi­ples, from natural philosophy and ana­tomy, as they properly afford a natural foundation and reason for all the methods that are now to follow, and to all the remarks that may occasionally offer, as we proceed. In the first place, sound is propagated by bodies elastic, and suscepti­ble of a vibratory motion. Secondly, pro­pagation of sound is interrupted by softer interposing parts, unsusceptible of any, or of but faint vibrations. Thirdly, the bones of the skull, in which the auditory nerves are lodged, form, with the upper maxil­lary bone, one continued hard and elastic body, uninterrupted in their connection by any softer parts, and hence extremely well adapted for the propagation of found.

As I have adduced these prepositions principally with the view that the at­tentive reader may have them constantly in his eye, either in passing a judgment on, or in explaining, the several methods, which, indeed, produce the sense of hear­ing by means of the auditory nerve, but [Page 27]not by the natural auditory channel, to which class also my own method, which I am now about to explain, does belong; so I shall at present, first, historically relate the several imperfect attempts of this kind: And then, secondly, describe my own method, in all its circumstances, and in the whole of the manner of procedure. Thirdly and lastly, explain it in its phy­sical and physiological principles, and at the same time determine the particular case, in which it is absolutely inapplica­ble.

We have extant experiments of a long standing, the first careful attention to which is generally, at least by Father Kir­cher, in his Musurgia universalis, P. II. p. 559. ascribed to the celebrated Neapo­litan John Baptista Porta; namely, that we can, for instance, hear the sound of a ringing fork, when striking its fore-part, or prongs, on another hard body, we hold its handle to the teeth. The very same thing is observable in a pair of tongs, a steel wire, a sword-blade, &c. when struck in the same manner, and applied to the teeth. Moreover, that we distinctly hear [Page 28]all the tones or notes of a musical instru­ment, when played upon, on taking it in the teeth, or touching it with a wire, sword-blade, &c. held in the same man­ner. Travellers, who happen to stray in the night, upon laying the head, especi­ally the hinder part, close to the earth, may hear distinctly, at the distance of a German mile or more, people going, ri­ding, or travelling. In this manner, some of the inhabitants of Halle could, on the neighbouring eminences, hear all the can­non fired in the glorious battle of Rosbach, in as distinct and plain a manner, as if at no great distance from the action, though at that time full four German miles off. Conrad Victor Scheider, so celebrated for his description of the mucose glands of the nose, in his book, De ossibus temporum, published at Wittemburg in 1653, in 8vo, p. 43, relates the same thing of some pea­sants, who sticking their staves in the earth, held one end in their teeth; to wave other instances at present.

All these experiments succeed as well, if not better, with deaf persons, than with those that have their hearing: As those [Page 29]last, upon stopping their ears, feel a ting­ling and whizzing from the included air, which the former are without. The proof of this I refer to the experience of all deaf persons who will make the trial. For, cases, where deafness cannot be relieved by this method, and which I shall men­tion towards the conclusion, are very rare: Nay, the practice of setting the mouth wide open, in difficulty of hearing, in or­der more distinctly to hear, is in some measure reducible hither: Though, in explaining this observation, I must differ from very great physicians, who would ac­count for this manner of hearing, solely from the air insinuated into the tuba Eu­stachii; which I shall more fully treat be­low.

That the methods of hearing but just mentioned, without the use of the ordi­nary organs of hearing, has been confirm­ed by the repeated observations of physi­cians and inquirers into nature, I shall briefly illustrate from some credible histo­ries, which may, at the same time clear up, and shew the different application of the method I am now upon. Boerhaave, [Page 30]a man, whose testimony is every where unexceptionable, tells us in his Praelecti­ones academicae in proprias institutiones me­dicas, T. IV. p. 414. according to Hal­ler's edition, of a deaf Musician, who, laying hold with his teeth in the upper parts of his lute, at the tuning pegs, played in a manner perfectly just, and ac­cording to all the rules of art, without the least mistake or blunder. Like in­stances we have in Ingrassias, in his Com­mentarii in Galeni librum de ossibus, Schelha­mer in his book De auditu, and in Du Verney, in his treatise on hearing.

Du Verney, just now mentioned, as also De Lanis, in his Magist. natur. & artis, p. 928, and others, have farther observed, that deaf persons have been enabled to hear extremely well, if, in speaking, one should direct the sound over and against the head. A curious instance of this we find in the Ephemerides academ. nat. curiosor. decur. i. ann. i. observ. xxxv. which is the more remarkable, as the principal cir­cumstance therein lies buried in the rub­bish of trifling quack medicines. Ema­nuel Ramiresius de Cariour, a Spaniard, is [Page 31]the inventor of this method, of whom Petrus a Castro, physician to one of the Dukes of Mantua, learned it, and to whom we owe the account. The whole of it consisted in the following particulars. In the first place, the patient, according as his constitution might require, was to use a proper laxative, and then once or twice a somewhat stronger purgative; after which the head was to be shaved at the coronal suture, for a hand's-breadth, and often rubbed, especially morning and eve­ning, with the following salve: Take three ounces of the best brandy, two drams of purified saltpetre, one ounce of oil of bitter almonds, set the whole to boil gently, till all the brandy is evaporated, then pour to it an ounce of orange water, (aqua naphae) stir it with a spatula, till it turns of the consistence of a thin salve. Lastly, early every morning the patient must clean, perfectly well, his head and eyes, and clear his ears and nose, rinse his mouth, and chew some mastich, or other fragrant substance, and then do his hair back with an ivory comb; this done, the speaker is to direct his voice just over the shaven [Page 32]part, and the deaf person comes to hear perfectly and distinctly every word that is spoken: And thus the deaf learn, not only to hear, but to speak. The reason of all this, will appear below.

But as the methed of Ramiresius is at­tended with many inconveniences, and as it must be very troublesome, not only to the patient, on account of such antecedent preparation, but to the speaker also. The following methods of producing this sense, by means of some elastic body held to the teeth, claim, by much, the preference: Of this the experiments adduced above are sufficient proofs. But the following account, taken from the Breslaw collection, Essay 21. p. 330. is still a fuller proof. A man at Copenhagen had, by distemper, lost his hearing, to such a degree, as not to have the least sense of firing of cannon, the beating ever so many drums, nor of any other the most violent motions: At last, he accidentally fell on a method, by which he could perfectly well understand any speaker, and write down all that he said; and this he did by means of a stick of wood, of a moderate length, one end of [Page 33]which he held to, or took in his teeth, rest­ing the other end against the place where the speaker stood. And thus at church he could understand the preacher, and write down the sermon, upon seating himself just under the pulpit, with his face towards it, and one end of the stick, while the other was between his teeth, resting against the foot of the pulpit.

About ten years since, John Paul Bau­mer, a young physician of Franconia, un­dertook to improve this method: And in a writing, which we shall presently men­tion, he pretended, he himself had devised the whole of the method, explaining it from the nature of the sense of hearing, and from the different manner of propa­gating sounds; but now and then some­thing escapes him, which bewrays, that he was not altogether unacquainted with that which others had attempted before him in that way. He published his me­thod in an inaugural disputation at Erfurt in 1749, under the following title, Pro­dromus methodi surdos a nativitate faclendi audientes & loquentes. The whole consists in taking a stick, made of an elastic body, [Page 34]or glass, steel, copper, bell-metal, silver, &c. flat and broad at both ends, to pre­vent its touching the lips; and being thus made fit for the due propagation of sound, one end of this stick the deaf person takes between his teeth, and the speaker the other, with this precaution, however, that neither of them shall touch the stick with the tongue or lips: In this manner, the deaf person hears every word that is uttered.

In order the more fully to establish the utility of this method, the author gives an instance in his second remark, § 6. of a young woman of twenty-four, who learned to hear in this manner, though with an old rusty piece of a sword-blade, about two feet long: For, upon pro­nouncing only a few words, she, with a smile, and pointing to her head, inti­mated, that she perceived every word that was said, and directly attempted to imi­tate them. But, as there are many defects in this method, as namely, that the stick must not be touched either with the lips or the tongue, in which case, all the lin­gual and labial letters, as b, d, f, l, m, [Page 35]&c must be uttered indistinctly; to obviate which, the author, indeed, has, § 15 and 17. of his disputation, proposed another method, by using an acoustic tube, and a speaking trumpet. If the first, the deaf person must take it in his teeth, and the speaker must pronounce at the wide end of the tube; which purpose a common funnel will answer as well: But if a speaking trumpet, the deaf person must open his mouth very wide, while the speaker, who pronounces through it, holds its upper broad part close to the teeth of the deaf person, yet without touching them.

CHAP. III. An account of the best and easiest method to make deaf persons hear.

TO conclude, all the methods hither­to metioned under this second class, are rendered far more commodious, more perfect, and of far more general utility, by considering a peculiar instance of an ingenious deaf person, who gave the great­est [Page 36]attention to every incident that offered to his observation: And this method I shall now propose at full length, as the easiest and best to enable deaf persons to hear. I am not, indeed, the first who published the account, and an explana­tion of it; as an unknown author, under the initial letters C, F, W. has already described it in the Harlem Journal for the year 1754, p 393. seqq. but as both his historical part is erroneous and imperfect, and the explanation of its circumstances, and the observations made thereon, are groundless and false; I had the whole matter more fully and more justly de­scribed, a year and an half since, in an academical disputation, defended under my presidentship, with the following title, Dissertatio sistens novae methodi, surdos red­dendi audientes, physicas & medicas rationes. But as such dissertations seldom come into the hands of any, but of physicians, I shall here, first, relate the history of this deaf person, in all its circumstances, toge­ther with the manner in which he reco­vered his hearing. Then, secondly, give a rational explanation, grounded on phy­sical [Page 37]sical and medical principles, of all the incidental circumstances observable there­in.

A reputable merchant of Wesel, in the Duchy of Cleves, a venerable, hoary, old man of seventy-eight, had, as early as his twentieth year, a great difficulty of hearing, which, as far as he could recollect, was occasioned, either by a violent fall, or by a profuse bleeding at the nose. The most promising means against this disorder proved ineffectual, it rather growing upon him from year to year, till, at last, he became quite deaf, unable to understand a single word, without bawling loud in his ears. Both German and Dutch physi­cians, who were consulted on this occa­sion, could not, with all their art and skill, afford any relief: At length, after an accurate examination of the external organs of hearing, the case was deemed incurable. However, he procured a variety of acoustic tubes from Amsterdam, in order to afford some relief to those who wanted to speak with him: But their use was afterwards laid aside, as being attended either with [Page 38]much inconvenience, or as never procu­ring any distinct degree of hearing.

Afterwards marrying, and having two of his eldest children, a son and a daugh­ter, taught to play on the spinnet, he often came up to it, and eagerly wished to hear the music: As the music-master once happened to say, that it was very possible for him to hear, if, according to an old, and well known experiment, he held a thin stick, or a tobacco-pipe, with the one end on the bridge of the sound-board, and with the other to the upper teeth; this he instantly tried, and was greatly pleased, that he could both plainly di­stinguish each note, and, as he thought, much stronger than formerly, at his best hearing. But all this was ineffectual to make him understand persons speaking, till an accidental trial procured him also this happiness.

In the year 1749, he had the good fortune to light, by mere accident, on a peculiar method, by which any person, at the distance of twenty, or even thirty paces, may, without greatly straining his voice, speak to be understood. This [Page 39]happened as follows: As one time this deaf person had all his family about him, and was pleasing himself with his daugh­ter's playing, by means of his tobacco­pipe; his brother, who happened to be present, alledged, that as he could plainly distinguish the sounds or notes of the spin­net, he might also, in the same manner, understand the articulate sounds of a spea­ker. For this purpose, his brother took a speaking-trumpet, and holding the nar­row part, or mouth-piece, to the upper teeth of the deaf person, he uttered a few words at the upper or wider part thereof: This trial, however, proved unsuccessful, the deaf man not being sensible of the least articulate sound. But he himself directly fell upon a device, which proved more successful. The brother was to hold the rim of the wide end of the speaking-trum­pet to his upper teeth, and he himself to do the like with the lower end, or mouth­piece: Upon which, his brother had scarce uttered a couple of words, but he directly repeated them with the greatest joy, and also assured him, that he under­stood them more distinctly than if he had [Page 40]bawled them in the loudest manner in his ear.

The deaf man did not stop here: In order to be convinced, whether the suc­cess was not owing to the structure of the speaking-trumpet, or whether the same thing might not succeed with other bo­dies; he directly tried, in the same man­ner, his tobacco-pipe, and a little wood­en stick, and to his great joy found it not only possible, but that the speaker might even speak as low as he pleased, so the voice were only audible. The curiosity of this man and his friends did not rest here; they wanted to know, at what di­stance one might converse with him: For this purpose, they took thin sticks or slips of wood, of different lengths, and one, in particular, six feet long, an inch broad, and of the thickenss of the back of a knife. At Wesel, and in the coun­try round about, they call such sticks flooring-slips or laths, which they use in filling up the openings of the boards of the flooring, when starting asunder: And such slips are the more commodious, as being thin, they the less hinder the pro­nunciation, [Page 41]and as in other respects, they produce the same effect in propagating sound: And even, by means of a bundle of them tied together, the lowest sound is distinctly audible, when the by-standers can scarce perceive any.

The farther trials and observations, which were made in the use of this me­thod, have been confirmed by the follow­ing experiments. In the first place, upon bawling in the loudest manner, in the mouth of the deaf person, through a large tin funnel, without touching the teeth, or even without the funnel, not a single word was understood. Secondly, if the slip of wood be held too fast with the finger, or laid hold on with shut lips, the voice proves very indistinct. But thirdly, if held with the teeth, the sensation is extremely weak. Fourthly, if the slip be held to the under teeth, there is not the least sense of hearing. Whereas, fifthly, the voice is perceptible and distinct, upon bringing, in using the slip, the tongue to the palate or to the teeth. Sixthly, the voice is less perceptible on joining the teeth together, than on their standing asunder. Seventhly, though the mouth be full of water, the [Page 42]hearing is not in the least diminished. Eighthly, when a brass or iron wire is held to the teeth, the deaf person hears nothing at all; but held between the teeth, a lit­tle. Ninthly, the deaf person may hear very well, on holding, by the lower rim, a beer-glass, to the upper teeth; or if, with the mouth shut, he presses it some­what hard just under the nose, and ano­ther person directs his voice up the glass, close to it; all which answers not with a wine-glass. Tenthly and lastly, the spea­ker must have good sound teeth, with­out any loose ones, at least in the upper jaw, as then the voice is very indistinct.

As the explanation of all the methods hitherto treated, and the observations oc­casionally offering thereon, are founded on the three physical and medical propo­sitions, advanced above; all that is neces­sary here, is to make a closer application of them to the present case, and from the consequences thence drawn, give a sufficient proof of the commodiousness and utility of the last method proposed, to procure hearing to the deaf. And thus, in the first place, I shall briefly handle [Page 43]the propagation of sound, so far as is ne­cessary to my present purpose. Secondly, mention those parts of the body, which either obstruct, or promote this propaga­tion. Thirdly, deduce from their several causes the peculiar observations, made in the foregoing paragraph. Fourthly and lastly, determine briefly those cases, in which the application of this method does not take place.

Inquirers into nature shew, that the propagation of sound depends principally on elastic bodies, that is, such, whose parts resist the action .of another body upon them, and which, when thereby altered in situation, restore themselves to their former state, from a force, not arising from their gravity, but peculiar to them. For, sound is nothing other but the tremulous, or vibratory motion, arising from elasti­city, of the minutest air-particles, whereby a peculiar sensation is produced in the au­ditory organs. Now, as this vibratory motion, and the sound produced thereby, are solely owing to the elasticity of bodies, we may thence fairly infer, that all elastic bodies are sonorous; for instance, glass, [Page 44]bell-metal, copper, silver, steel, &c. But, in order to one body's acting upon ano­ther, they must come either into mediate or immediate contact with each other. For, action at distance, actio in distans, is both, by physical and metaphysical prin­ciples, a non-entity, a mere fancy. Now, as daily experience shews, that sound takes its rise at a distance from the ear, and thus only mediately, namely, by ano­ther intervening body, puts in motion the auditory organs; it follows hence, that the body producing this mediate ef­fect, must be elastic, as the propagation of sound is not possible by means of any other body.

The elastic body, which commonly propagates sound, is the air; but it is possessed of this virtue from no other quality, but from that of its elasticity. Consequently, all elastic bodies without exception answer this purpose, so that they only affect the organs of hearing, or are continuous with them. Of this we have undoubted proof from well-known expe­riments. Besides the instances adduced above, it is a thing we may daily ob­serve [Page 45]in musical instruments. The tremor or vibration, imparted to the string of a spinnet or violin, and the like instruments, is propagated from it to the bridge, and thence again to the sound-board; and in the instance we are now upon, from the bridge of the spinnet to the tobacco-pipe, and thence farther on, till it reaches, and puts into a similar motion, the organs of hearing; and the parts themselves of our body are adapted for this propagation. For instance, hang a little bell, cymbal, pair of tongs, &c. by means of a metal wire or gut-string, on the finger, and with that finger stop the ear, and strike upon or move any of these bodies, and the sound is perfectly well perceived: Or take a watch by the chain between the teeth, and stop the ears close, and you will very di­stinctly hear it go.

As in these cases, the sound is propa­gated from the mouth to the ear, though the air, which is put in motion, is no ways connected with the external ear; in that case it must be, that the parts of the head, lying between the mouth and the organ of hearing, are the means of [Page 46]propagation. But as it is well known from physical grounds, that soft parts, susceptible of little or no degree of vibra­tion, are not only in themselves incapable of propagating sound, but even obstruct, or, at least, diminish its farther propaga­tion, when happening to interrupt the connection of the hard and elastic parts: The hard and elastic parts, therefore, of the body, uninterrupted in their close connection or continuity by the inter­vention of softer parts, are alone fittest for this purpose.

I shall now briefly mention, as I pro­mised above, all these hard parts of the head, with their several connections with each other; from all which, their capa­city or incapacity to propagate sound will be more easily and certainly determined; and shall begin with the under parts, where, according to the experiments above mentioned, the communication and pro­pagation of sound took its rise; and thus shall proceed to the upper parts. And first, the teeth offer to consideration, which are parts extremely hard and firm, and by an articulation, called gomphosis, [Page 47]wedged or fixed immoveably in their ca­vities or sockets, in both the jaw-bones, so as not to drop out even in a skeleton. In the second place, follows the under jaw-bone, both whose apophyses condyloi­deae are obliquely inserted in the fovea gle­noides of the temporal bone, and move over the oblique eminence of the same bone, by means of the cartilago interar­ticularis. Thirdly, the upper maxillary bones come to be considered, whose hin­der and inner part is immediatly connected with the apophyses pterygoides of the os sphenoides; but the fore-part firmly con­nected with the palatine to the ossa palati, and with the zygomatic processes to the os zygomaticum. Then, fourthly, follows the just mentioned os jugale, or zygomati­cum, which, by a peculiar process, is closely connected, backwards, with the temporal bone. Fifthly, the palatine bones are connected with the os cuneiforme by the pterygoidal processes. Sixthly, the os cuneiforme lies in the middle, between the said bones, and forms, as it were, the common copula or tie of these and of the temporal bones; seeing it is connected [Page 48]forwards with the palatine bones by the pterygoid processes, and by the temporal processes, called by some the greater wing of the os cuneiforme, with the os squamo­sum and petrosum of the temporal bone. Hence, seventhly, it appears, that the temporal bone is immediately connected with the os jugale and cuneiforme, and me­diately with the palatine bones, and both the maxillary bones, and with the teeth; yet so, as that the connection with the inferior maxillary is interrupted by an in­terposing cartilage. Eighthly, the con­nection of the temporal with the other bones of the cranium, as the ossa frontis, sincipitis, and occipitis, is either mediate, by means of the os cuneiforme, or imme­diate, by means of the sutures; which last, in more advanced years, intirely dis­appear. Ninthly and lastly, to this head we refer the tuba Eustachii, a canal, part­ly bony, partly cartilaginous, and partly membranous, and closely connected with the temporal bone.

From this connection of bones, we may plainly see, that sound is propagated by such of them, as are continuous, and [Page 49]closely connected together, and are, as much as may be, either bare and naked, or only covered with thinly expanded soft parts: Of this kind are principally the upper teeth, then the upper maxillary bone; also all the bones of the cranium, when stript of their hair, and their other softer parts, are a little stretched, either by the hand, or some astringent. And this is the foundation of Ramiresius' method, very easily explicable from that which we have just said. On the contrary, where there is neither no perfect and continuous connection of bones with each other, par­ticularly with the temporal, which con­tains the internal ear, or where too many softer parts lie round or between the bones, the propagation of vibratory motion, and consequently of sound, is, according to phy­sical principles, impossible: On this ac­count, neither the under maxillary bone, nor the tuba Eustachii, can properly propa­gate sound. Of the last we are, moreover, to observe, that being membranous from the pterygoid processes to its opening into the mouth, and partly also lax, and on that account exhibiting a somewhat collapsed [Page 50]passage, the vibrating air cap neither be conveyed in sufficient quantity, to the cavity of the drum, nor produce in it the due vibratory motion.

As sound may be propagated by all ela­stic bodies, in close connection or con­tact with each other; so in this case may be of service all thin slips of wood, Spa­nish reeds, sword-blades, tobacco-pipes, &c. when pressed to the above-mentioned hard and elastic parts of the head, which stand connected with the temporal bones. Now, as among all the elastic bodies just mentioned, the fibres of wood are remark­ably tough and flexible, and on account of their loose and open texture, give no great resistance to vibratory motions, but rather afford them greater scope; so thin slips of wood, or slender Spanish reeds, are best adapted for the purposes of propagating sound to the elastic parts of the head, and to the organs of hearing.

From the principles hitherto advanced, may be explained all those experiments, which were made on occasion of actually employing this method, and briefly recited above. The first experiment, either with [Page 51]the large funnel, or with barely speaking into the mouth of the deaf person, in or­der to produce the sense of hearing, mis­carried in the execution: For, as in this case, the air alone is to communicate to the teeth, and other elastic parts connect­ed with them; a vibratory motion; it is in general unfit for this purpose, as it comes greatly rarified from the mouth of the speaker, and consequently, greatly dimi­nished in activity and elasticity: Besides; from the property common to all forced fluids, as soon as it has escaped the mouth of the speaker, it expands every way, and thereby becomes still more weakened in its efficacy, and consequently cannot, in that case, overcome the resistance of the teeth, and other elastic parts of the mouth of a deaf person, nor put them into vibra­tory motion, sufficient to produce the sense of hearing.

The second, third, and sixth experi­ments, in which the voice proved too weak and imperceptible to the deaf man, when the slips of wood were held too fast with the singers, or shut lips and teeth, as also when held to the shut teeth, may be [Page 52]explained in the same manner. From the foregoing propositions it is evident, that the softer parts of our body interrupt the progress of sound, receiving indeed the vibratory motion, but for want of the re­quisite re-action not propagating it far enough: And for this there is also ano­ther reason, namely, that in the three for­mer methods of applying the slip of wood, the same degree of force must put in mo­tion a far greater quantity of the vibratory air, than can happen in different and op­posite circumstances, whence, of necessity, a less effect must ensue: Now, as in the third and sixth experiments, a greater share of vibration is lost in the under jaw-bone, the sensation thereof must, of course, be extremely weak and indistinct.

And this farther explains the fourth ex­periment, by which the deaf person per­ceived not the least sound, on holding the slip to the under teeth. To explain this observation there can be no difficulty, when we recollect the connection of the under jaw-bone with the temporal: The under jaw-bone having its connection with the rest of the bones of the head, only by [Page 53]means of soft interposing parts, namely, a soft cartilage, which, besides, on account of the constant moistness of those parts, is lower, receiving, indeed, the vibratory motion, but directly again losing it, and, as it were, deadening it, in its softer sub­stance, for want of the requisite re-action; how is it possible then to expect any alte­ration in the other bones of the head from the vibratory motion of this bone?

The fifth experiment, on the contrary, is somewhat more difficult to explain: For, as here the tongue, a softer part, is brought to the palate and teeth, and yet that which another utters remains distinct and perceptible to the deaf person, it should seem, that this experiment contra­dicts the second, third, and sixth.

But here we are to consider, that, in the first place, the tongue is applied be­hind the teeth. 2dly, That all soft parts, as fully appears from physics, receive not such a quantity of vibratory motion, as do hard bodies: Whence it is, as the teeth are as it were wedged in the upper ma­xillary bone, being a hard part, the greatest share of vibration will go to the jaw, and [Page 54]only a smaller share thereof to the tongue: But, if you slip the tongue forwards over the teeth, the same thing happens as in lips together; either no sound at all, or but very indistinctly, being perceivable by the deaf person.

The seventh observation, namely, that the hearing is not diminished, though the mouth be full of water, is easily accounted for; as we learn from philosophy, that there is much elastic air in water, adapted for the propagation of sound; as suffici­ently appears from the example of divers, who, under water; perceive the sound produced above water: Now, as water perfectly encreases the continuity of the parts in the mouth, and propagates the vibrations produced by sound from the teeth to the maxillary bones, and the pterygoid processes of the os cuneiforme, we may, from the connection of these parts with the temporal bones, easily judge, that the sensation of sound is rather heigh­tened than diminished by the water in the mouth.

In order to explain the eighth experi­ment, which was made with a brass or [Page 55]iron wire, two things, in particular, are to be remarked; first, that such metal strings or wires are a great deal firmer than wood, and consequently require a greater degree of force, in order to vibrate, than is possible to be produced by the air in speaking: Secondly, that their base of contact with the teeth is by much too small, for them to communicate a suffici­ent degree of motion to the whole range of bones reaching quite to the ear: And this is the very reason, that by laying hold on it with the teeth, the points of contact being encreased, the deaf person comes to have some degree of sensation.

The happy effects produced with the beer-glass, and the unsuccessful attempts with the wine-glass, which was the ninth experiment, seem to depend, either on the greater compass of the former, or on some degree of compression pro­duced in the air spoken into it, which thereby communicates its vibratory motions and repercussions to the elastic glass, and by that means to the teeth and upper jaw­bone, though the lips interpose or lie be­tween, as they acquire a greater degree of [Page 56]closeness in their texture, and greater sus­ceptibility to propagate sound, by the greater degree of pression, made on them with the rim of the glass: Whereas, a less portion of air goes into the wine-glass, besides, its compass is smaller, and the greater mass of foot or stalk, diminishes the motion of the air, so as to prevent its communicating to the teeth a sufficient pitch of vibration. And lastly, the reason why, according to the tenth observation or experiment, the loose teeth of the upper jaw rendered speaking indistinct to the deaf person, is easily understood, when we reflect, that, in order to propagate a vibra­tory motion, a closer continuity of elastic parts is requisite.

As the sensation, which is perceived in the act of hearing, produced by the me­thods of the second order of the second class, seems to be formed almost in the middle of the brain, backwards at the me­dulla oblongata, we may hence, according to anatomical grounds, judge, that the vi­brations produced by sound, put the audi­tory nerves in sensation, from the os petro­sum, quite to their origin: And hence [Page 57]arises this practical proposition, that the easy method we have been hitherto upon, to procure hearing to the deaf, is adapted to all persons afflicted with deafness, be the other auditory organs injured how they may, provided the auditory nerves are not ob­structed, injured, or quite destroyed at their origin: For, this last is the only case, in which the present method is not applicable, and on such melancholy objects all labour and pains are lost.


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