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.