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 contray, 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.