NEITHER FOR HEARING IS THE AIR NECESSARY AS A MEDIUM.
5. As to hearing, there are several theories. One is that the air is first set in motion, and that this motion, being transmitted unaltered from point to point from the (location of the) sound-producing air as far as the ear, causes the sound to arrive to the sense. Again, another theory is that the medium is here affected accidentally, and only because it happens to be interposed; so that, if the medium were annihilated, we would feel the sound immediately on its production by the shock of two bodies. We might think that the air must first be set in motion, but the medium interposed (between the first moved air and the ear) plays a different part. The air here seems to be the sovereign condition of the production of sound; for, at the origin of the sound, the shock of two bodies would produce no sound if the air, compressed and struck by their rapid concussion did not transmit the motion from point to point as far as the ear.[173] But if the production of the sound depend on the impulsion impressed on the air, the (qualitative) difference between voices and (instrumental) sounds will challenge explanation; for there is great difference (of "timbre") between metal struck by metal of the same kind, or another. These differences are not merely quantitative, and cannot be attributed to the air which (everywhere) is the same, nor to the force of the stimulus (which may be equal in intensity). Another theory (of Aristotle's) is that the production of voices and sound is due to the air, because the impulsion impressed on the air is sonorous. (To this it should be answered that) air, in so far as it is air, is not the cause of sound; for it resounds only in so far as it resembles some solid body, remaining in its situation, before it dilates, as if it were something solid.[174] The (cause of the sound) then is the shock between objects, which forms the sound that reaches the sense of hearing. This is demonstrated by the sounds produced in the interior of animals, without the presence of any air, whenever one part is struck by some other. Such is the sound produced by certain articulations when they are bent (as, the knee); or certain bones, when they are struck against each other, or when they break; in this case air has nothing to do with the production of the sound. These considerations compel a theory of hearing similar to our conclusions about sight. The perception of audition, like that of vision, therefore consists in a repercussion (an affection sympathetically felt) in the universal organism.
THE RELATION OF THE AIR TO THE LIGHT.
6. Could light exist without air, if the sun illuminated the surface of bodies, and if there were a void in the interval which is accidentally illuminated by virtue of its location (between the sun and the bodies)? It is certain that if the other things were affected because the air itself was affected, and if light were nothing more than an affection of the air, that is, its substance; then indeed this affection could not exist without the experiencing subject (the air). But (in our view) light is not essentially characteristic of air as such; for all fiery and brilliant bodies, among which are precious stones, possess a luminous color. Could that which passes from a brilliant body into some other body exist without that other body? If light be but a simple quality of an object, and as every quality implies a subject on which it depends, light will have to be sought in the body in which it resides. If, on the contrary, light be only an actualization produced by some other thing, and if there be no body contiguous to the luminous object, and it be entirely surrounded by a void, why could light not exist, and radiate upwards (as well as downwards, and in every direction)? Since light radiates, why should it not radiate without hindrance? If its nature be to fall, it will spontaneously descend; for neither the air nor any illuminated body will make it issue from the illuminating body, nor can force it to advance, since it is neither an accident that implies a subject, nor an affection that implies an affected object. Otherwise, the light would remain (in the illuminated body) when the object from which it emanates should happen to withdraw; but since the light withdraws with it, it radiates. In what direction does light radiate? (Its radiation) demands no more than the existence of sufficient space; otherwise the body of the sun would lose its actualization; that is, the light it radiates. In this case light would not be the quality of a subject, but the actualization that emanates from a subject, but which does not pass into any other subject (as a kind of undulation); but if another subject be present, it will suffer an affection. As life, which constitutes an actualization of the soul, affects the body if it be present, and does not any the less constitute an actualization if the body be absent, likewise light constitutes an actualization subject to the same conditions. It is not the obscurity of the air that begets light, nor obscurity mingled with the earth which produces an impure light; otherwise one might produce something sweet by mingling some thing with what is bitter. The statement that light is a modification of the air, is incomplete without the addition that the air must itself be modified by this modification, and that the obscurity of the air is no longer obscure after having undergone that change. The air itself, however, remains what it was, just as if it had not been affected. The affection belongs only to that which has been affected. Color therefore does not belong to the air, but subsists in itself; the air's only function is its presence. But enough of this.
DOES THE WITHDRAWAL OF THE LUMINOUS SOURCE ABANDON THE LIGHT TO DESTRUCTION; OR DOES THE LIGHT FOLLOW IT?
7. It might be asked whether the withdrawal of the object from which light emanates abandons the light to destruction, or does the light follow the source into withdrawal? This question is related to the former one; (and it may be said that) if the light inhere in the illuminated body in a manner such as to have become characteristic of it, the light perishes with it. The light is an immanent actualization, for otherwise it would surround the object from which it emanates, and remain within it, accumulating there. If this were so, the light could not vanish so long as the object from which it emanates itself continues to subsist. If this object pass from one place to another, light would pass thither also, not because it turns back on itself or changes locality, but because the actualization of the luminous object exists and is present as soon as nothing opposes it. If the distance from the sun to the earth were much more considerable than it really is, the light of the sun would nevertheless reach us, providing no obstacle were interposed. On the one hand, there is in the luminous body an actualization, a kind of superabundant life, a principle and source of activity; on the other hand, beyond the limits of the luminous body, exists a second actualization which is the image of the actualization characteristic of this body, and which never separates itself from the body. Every being has an actualization which is its image; so that, as soon as the being exists, its actualization exists also; and so long as the being subsists, its actualization radiates nearer or further. Actualizations (differ indeed); some are feeble and obscure, others are secret or hidden, others are powerful and radiate afar. When an actualization radiates at a distance it must be admitted to exist there where it acts, where it exercises and manifests its power. Consequently one can see light shine from the eyes of animals whose eyes are naturally brilliant[175]; likewise when the animals that exert a concentrated interior fire happen to open their eyelids, they radiate rays of light into the darkness; while, when they close their eyes, no more light exists outside them. The light therefore does not perish; only, it is no longer produced exteriorly. It does not re-enter into the animal but merely ceases to exist exteriorly, for the visual fire does not pass outside, remaining inside. Is light itself then within? At least this light remains within; but (when the eye is closed) the eyelid forms an obstacle to its diffusion.
LIGHT AS ACTUALIZATION IS THE BEING OF THE LUMINOUS BODY, AND IS INCORPOREAL.
Thus the light that emanates from bodies is the actualization of the luminous body which is active exteriorly. The light in the bodies whose original nature is such, is the formal being of the originally luminous body. When such a body has been mingled with matter, it produces color. The actualization alone does not suffice to give color; it produces only the hue, because the actualization is the property of a subject, and depends on it, so that nothing can be withdrawn from the subject without simultaneously being withdrawn from its actualization. Light is entirely incorporeal, though it be the actualization of a body. It could not therefore properly be said of light that it withdraws or is present. The true state of affairs is entirely different; for the light, so far as it is the actualization of the luminous body, is its very being. The image produced in a mirror is therefore an actualization of the visible object, which acts on anything that is passive (that can suffer, or experience), without letting any of its substance escape by any wastage. If the object be present, the image appears in the mirror; it is as it were the image of the color that possesses some particular figure. When the object withdraws, the diaphanous body no longer possesses what it possessed while the visible object was acting on the mirror. A similar condition is that of the soul; her actualization dwells within the (world's) body so long as this soul herself dwells within it.
LIFE AND LIGHT DO NOT PERISH, BUT ARE NO MORE THERE.
(Curiosity might lead some one to ask about) a force that were not the actualization of the Soul, but which only proceeded from this actualization, such as the life which we say is proper to the body. Is the case of such a force similar to that of the light characteristic of bodies? We said that the light inheres in colored bodies, so far as that which produces the colors inheres in the bodies. As to the life proper to the bodies, we think that the body possesses it so far as the soul is present; for nothing can be inanimate. When the body perishes, and when it is no longer assisted by the soul which communicated life to it, nor by the actualization of this soul, how should life remain in the body? What! Has this life perished? No: this life itself has not perished, for it is only the image of an irradiation; it would not be correct to say more than that it is no more there.[176]