# On the Vital Principle/Book 2/Chapter 8

Let us now proceed to determine the nature of sound and hearing. Sound is double—one actual and another potential; for we say that some substances, such as sponge and wool, are without sound; and that others, as brass, and bodies which are hard and smooth, have sound, because such objects are able to sound; are able, that is, to create actual sound by the action of the medium between the object and the hearing. Sound of the actual kind is the invariable result of something in relation to something and in something; for its producing cause is percussion. It is impossible, therefore, that sound should be produced when there is only one substance, as that which percusses must be distinct from that which is percussed; so that the sonorous object sounds by its relation to another object. But there can be no percussion without movement, and sound is not produced by the percussion of any kind of substance, as we have said, (since wool, however percussed, does not, while brass and smooth and hollow bodies—brass because it is smooth—do give out sound,) and hollow bodies create, by reflexion, many percussions after the ​first, owing to the medium within them having been set in motion and being unable to make its escape. Sound is audible in air, and so it is in water, although less distinctly; but neither air nor water is the efficient cause of sound, as for it there must be percussion of solid bodies against each other and against the air, and this is effected whenever the air, having been percussed, remains, is not, that is, dispersed. Thus, if the air be struck sharply and forcibly it gives out sound; for the motion of that which percusses should anticipate the dispersion of the air, as if any one were striking a rapidly moving heap or cloud of sand.
An echo is produced whenever the external air has been more than once repelled by the air contained within a vessel, by the sides of which that air is precluded from being dispersed, just as a ball rebounds. It seems as though an echo ought to be a constant occurrence, although it may not be audible, since that happens to sound which happens to light, and light is continually undergoing reflexion (for, otherwise, as light could not be everywhere, darkness would prevail beyond the spot illumined by the sun), but yet it is not everywhere reflected, as it is from water or brass or any other smooth body, so as to form a shadow whereby we are able to distinguish the light itself.
A Void is rightly said to be the sovereign cause of hearing;—for the air seems to be a void, and the ​air, when moving continuously and as one body, is creative of hearing. But, owing to its being very diffluent, it gives out no sound, unless that which is percussed be smooth; when this, however, is the case, the air becomes simultaneously one over the surface, as the surface of every smooth body is one. Every sonorous body is so constituted as to set in motion the air which, by continuity, is one up to the hearing, and the hearing is naturally connected with the air; and owing to sound being in the air, the air which is without sets in motion that which is within. An animal, therefore, does not hear everywhere, neither does the air penetrate everywhere; for the part to be set in motion is a living part, and does not everywhere contain air. The air itself, owing to its ready diffusibility, is without sound; but, when precluded from being dispersed, its motion is productive of sound. The air which is within the ears has been so immured as to be immovable; and this in order that the sense may perceive accurately all variations of its movement. It is for these reasons that we are able to hear when in the water, as the water cannot gain access to the congenital air, or pass into the ear through the convolutions; when, however, this does happen, there is no hearing, any more than there is when the membrane of the ear, which is to it what the skin over the pupil is to the eye, is diseased. But proof is afforded whether the hearing is perfect or not, in that the ear ​is constantly giving out sound, just as a horn does; for the air within the ears is continually moving in some peculiar manner, and yet sound is foreign to that air and forms no part of its properties. It is on this account, however, that we speak of hearing by a void and something resonant, because we hear by the part which contains the air confined within it.
But is it that which percusses, or that which is percussed, which gives out sound ? Or do both contribute to its production, each in its own way? Now, sound is the motion of something which admits of being moved after the manner of bodies rebounding from smooth surfaces, whereon they may have been impelled. But every kind of body, whether percussing or percussed, does not, as has been said, give out sound ; as when a sharp point, for example, strikes a sharp point, there is no sound; but in order to produce sound, that which is percussed must be so smooth, that the mass of air upon its surface may rebound from, and be agitated over it. The distinctions among sonorous bodies are revealed in the actual sounds which they give forth; for as without light colours are not visible, so without sound the acute and grave are not audible. These terms (acute and grave) are derived from tangible properties, and employed, in a metaphorical sense, for sounds; for the acute moves the hearing quickly and sharply, the grave moves it slowly and dully; not, however, that ​the acute is quick or the grave slow; but that such is the motion of the one from the celerity, and such the motion of the other from the tardiness of its operation upon the sense. And there does seem to be an analogy between those sounds and the sharp and blunt, as perceived by the Touch; for the sharp pricks, and the blunt pushes, as it were, because the motion exerted by the one is rapid, by the other tardy; and it is in this manner that the terms in question have originated. Let us here, however, close our observations upon the nature of sound.
The voice is a sound produced by a living creature; for nothing inanimate speaks, although there are objects, such as the flute, lyre, and others, which, having range of note, harmony, and expression, are said, from a resemblance between their tones and the voice, to do so; and the voice does seem to have all the variations of note possessed by those instruments. Many creatures have no voice (as all the insanguineous, for instance, and some of the sanguineous, as fishes), which is very understandable, seeing that sound is a certain motion of the air; and with respect to those fishes which are found in the Achelous and said to speak, they produce sound by their gills, or other such part. But although the voice is a sound emanating from a living creature, it does not imply any kind of sound, or a sound produced by any kind of part; and as all sound is produced by the ​conditions of something which percusses, something percussed, and a something, that is the air, in which percussion can be made, it might reasonably be assumed, that such creatures only as take in air can have a voice. Now, nature employs simultaneously the air respired for two functions, just as she employs the tongue for taste and for speech; and of these the former is necessary (and therefore imparted to most creatures), and the latter, as an organ for interpretation, is for their higher good; so too does she employ the breath both as necessary for tempering the heat within (as shall be explained elsewhere), and for the production of voice, which is for the welfare of the individual. The pharynx is the organ of respiration, for the sake of which is another part, the lung, and it is owing to this part that quadrupeds have more heat than other creatures.
It is the place about the heart which first needs respiration; and, therefore, it is necessary that the air, during inspiration, should pass inwards; and thus the percussion of the air respired by the living principle in those parts, against the so-called trachea, constitutes the voice. But every sound produced by an animal is not voice, as we have said (for it is possible to produce sound by the tongue, as in coughing), but in order to constitute the voice, there must be a percussing living force, and the sound produced must be expressive of something. The voice is, in fact, a ​sound expressive of something—it is not, that is, as in coughing, a mere sound of the air inspired; and speech is the percussion, by the living principle, of the air in the trachea, against the trachea itself. As proof of which, we are unable to speak when holding the breath, that is, when we neither inspire nor expire; for the act of holding the breath sets in motion the air which is inspired. It is now manifest why fishes, having no pharynx, are without a voice; and they have no pharynx, because they neither admit the air nor breathe. It is foreign to our present purpose, however, to inquire into the cause of their having been thus constituted.

## Notes

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​Note 1, p. 100. Sound of the actual kind is the, &c.] As sound is the result of percussion, the passage implies something to be percussed, as well as something in which that which percusses is to move; but what that something is in which percussion is to be made is not explained. Some commentators, as Simplicius, have considered the words ἐν τινι to imply, "the air which is interposed between the sonorous body and the sense," and which, but for the contradictory opinions of that age with respect to the air, might be at once accepted as its meaning; and even taken as some special medium, as has been suggested, it still may signify a body of air. We ​may consider the voice, Plato observes, as percussion (sound, that is,) transmitted, by the air, through the ears, brain and blood, to the sentient principle. But as the nature and properties of the air were then, from the want of experimental science, unknown, they were available for any hypothesis; and yet there is evidence that Aristotle, not to add Plato, did regard the air as essential to sound and voice. Aristotle, while agreeing with most philosophers in ranking air among the four elements, "sees a difficulty in determining what its nature may be in the universe around the earth, or what its order in relation to the other elements of bodies." He was aware of the air holding water in solution, and observes that, whether water be or be not produced, equally, from the whole air, that which is around the earth must be not air only but vapour, which is again to be condensed and become water. Thus, "we maintain," he adds, "that fire and air, water and earth are producible out of one another, and that each of them is present, in potentiality, in each of the others; as is the case with all bodies, which have a base into which each of them is ultimately reducible." He has distinguished the air we inspire from that which we send forth (ἐκπέμπειν) and to which he has given a specific appellation (τὸ πνεῦμα); but owing to the difficulty of determining either its nature or its office, (although it is the subject of a special treatise,) no ​unexceptionable equivalent for it can be offered. These quotations shew, amid many suggestive observations, that knowledge concerning the air was then very unsettled; and yet they prove, it may be assumed, that air was implied in the passage referred to.
Note 2, p. 101. An echo is produced whenever, &c.] This passage is obscure, both from its elliptical wording and the want of adequate exemplification; but, in attributing to the air elasticity and capability of being reflected, it seems to suggest that the atmosphere only is the cause of sound and, therefore, of echoes. So, according to modern science, "an echo is sound reflected from a distant surface and repeated to the ear; although several other conditions are required for its production." In another treatise, it is assumed that reflexion of the air (ἡ ἀνάκλασις) is the immediate cause of an echo; and since an echo is reflexion, "must there not be, for its production, air confined, impacted and communicating, as one mass, with that which is to be reflected?" But an echo, whether or not audible, ought, as the text states, looking at the properties of the air, to be a constant occurrence; for as light is continually reflected from bodies, and thereby casting shadows by which light is distinguished, so sound, owing to the air's elasticity, must be often reflected and, therefore, repeated, in varying degrees of intensity, according to the nature of the surface on which it may have impinged. That age, in fine, was ​acquainted with several of the properties of the air, but, as they had not been tested experimentally, its acquaintance with them was but conjectural, and could lead to no positive inference; it was reserved for modern science to ascertain what the air is, and what its properties in relation to the world, its productions and inhabitants.
Note 3, p. 101. A void is rightly said, &c.] It would be difficult even to conjecture what could have been meant by a void in that age ; for although it had been perceived, it may be but obscurely, that the air rises by fire (heat) to the upper regions and becomes ether, (as in the Timæus, expiration is accounted for by the rising up from within of the heated breath,) yet it is not to be supposed that rarefaction was an admitted property of the air, or that any condition like rarefaction was implied in the void. Aristotle observes, upon this topic, that, "according to some philosophers, a plenum is a space or vessel when full, and a vacuum or void is the same when empty, thus making, as he says, the plenum to be identical with the vacuum and space, excepting in conditions of relation." In all this it is evident that no account was taken of the air; and he objects to Anaxagoras, (who had shewn, experimentally, that the air is substance of some kind,) that he argues against what had never been contended for—the advocates for a void maintain, he says, that it is a space in which there is no tangible body, and, holding every ​thing to be corporeal, they consider that only to be a void in which there is absolutely nothing; so that it can be to no purpose to shew that the air is something. This epitome shews sufficiently how widely apart from one another are the antient and modern significations of a void, since it now implies such a rarefaction of the air as can be obtained through the air-pump; and, as rarefaction cannot be carried beyond 300 times, no proof can be afforded of the possible existence of a void. Aristotle objects to those who maintained that the void is identical with any space filled with air, "for, if the air be driven out, the space will clearly, he observes, be a void, in a stricter sense than it was, since it will no longer be full of air." But it would be foreign to the purport of these notes to inquire further into the opinions of that age; it may be inferred, however, from what has been adduced, that Aristotle, although he refused corporeity to the air, was not a very consistent supporter either of the plenum or vacuum.
Note 4, p. 102. Every sonorous body, &c.] This passage is a summary of all that physiology has now to offer upon sound and hearing; but although it might have been surmised that sound is vibration of the air, caused by a sonorous body and conveyed, by successive undulations, to the organ of hearing, yet, as the internal ear was then unknown, it is a surprising assumption that air must be contained within the organ, in order that the ​vibration may be communicated to the sense. Aristotle may perhaps have been led, notwithstanding the unstable opinions of his age upon the air, to conclude that, as sound "is present in the air," air must be connected with the hearing, and, if so, be contained, naturally, within its organ. The succeeding passages hardly admit of comment, on account of their evident want of anatomical knowledge; but they prove that the tympanic membrane had been made out, as also that it may be so injured, as to admit fluid from without into the ear. And this disease of the membrane is aptly compared to ulceration and consequent opacity of the eye's membrane, (the cornea,) whereby the rays of light are precluded from entering the eye and producing vision.
Note 5, p. 102. But proof is afforded, &c.] This somewhat puerile experiment is still extant. It seems strange that the very obvious cause of this phenomenon did not occur to one who had surmised, without anatomical proof, that there is air within the tympanum; it had escaped Aristotle, besides, that, in a former passage, he had made the air which is immured within the ear to be immovable.
Note 6, p. 104. The voice is a sound, &c.] This passage is a clear definition of the voice, and it points, although indistinctly, to the parts and functions concerned in its formation. The voice is said to be different from sound, and speech to be different from either; and, as ​speech can be produced by no other part than the pharynx, those creatures only can speak which have lungs, as speech is the articulation of the voice by the tongue. Wherefore, the voice and larynx send forth vowels, the tongue and lips consonants, and these together make up speech. So, too, Cuvier says, that "man alone among animals can articulate sounds, owing probably to the form of his mouth and the mobility of his lips." The pharynx, so called, and trachea, are of cartilaginous nature, and this because they are for the sake of the voice as well as breathing; and it is necessary that that, which is to give out sound, should have firmness as well as smoothness. But the larynx and pharynx are here alluded to as if they were one and the same organ, and it may be, that owing to the complicity of the parts and their multiplied relations to one another, they were then so considered; but yet passages might be cited, which seem to shew that they were known, both by function and position, to be different organs.
Note 7, p. 105. Nature employs, simultaneously, the air, &c.] It was assumed by the physiologists of that and, indeed, many subsequent ages, that the office of respiration is merely to cool the blood, or rather to temper its heat, which was supposed to be constantly tending to an excess incompatible with life. In modern times, on the ​contrary, the action of the air which is inspired upon the venous blood has been by some regarded as a process of combustion, and the source, through combustion, of the special temperature which characterises all organised and living bodies. Respiration is said, by Grant, to be essential to the constitution of animal bodies; for by this function "the vital fluids are purified and replenished, the muscular system is furnished with its capability of action, and the high temperature of the mammalia is preserved in every condition of the surrounding element."
Note 8, p. 106. As proof of which we are unable, &c.] The meaning of this passage, owing in part to the unsettled knowledge of that age, is by no means evident; but it can be readily admitted, that the act of holding the breath must set in motion, disturb, that is, the air which has been inspired, and produce coughing rather than articulation. The French commentator makes the text (κινεῖ καὶ τοῦτο) to imply "disturbance of the function;" Trendelenburg, however, sanctions the version here given. It will be apparent, from what has been adduced, that the word pharynx (of fishes) should have been larynx, for this, being the upper part of the trachea, is the tube which conveys air to the lungs, as the other, being the upper part of the œsophagus, is the tube which conveys food to the stomach; and all fishes have a pharynx, of course, but, as they do not breathe, they are without a larynx.
* ↑ Timæus, 67 B.
* ↑ Meteorologica, I. 3. 3. 2.
* ↑ περὶ πνεῦματος
* ↑ Brande's Hist, of Science.
* ↑ Problemata, XI. 8.
* ↑ Meteorologica, II. 2.
* ↑ Nat. Auscult. iv. 6. I.
* ↑ Topica, vii. i. ii.
* ↑ Hist. Animalm, iv. 9. i.
* ↑ Anatomie Comp. t. I. 15.
* ↑ De Part, Animalm, vii. 3. 5.
* ↑ Ibid. ii. 3. 9 ; iii. 3. 2.
* ↑ Outlines, p. 592.