and Epicurus suppose that sight is caused by the insertion
of little images into the visive organ, and by the reception of certain
rays which return to the eye after meeting the object. Empedocles
supposes that images are mixed with the rays of the eye; these he styles
the rays of images. Hipparchus, that the visual rays extend from
both the eyes to the superficies of bodies, and give to the sight the
apprehension of those same bodies, after the same manner in which the
hand touching the extremity of bodies gives the sense of feeling. Plato,
that the sight is the splendor of united rays; there is a light which
reaches some distance from the eyes into a cognate air, and there is
likewise a light shed from bodies, which meets and joins with the fiery
visual light in the intermediate air (which is liquid and mutable);
and the union of these rays gives the sense of seeing. This is Plato's
corradiancy, or splendor of united rays.

CHAPTER XIV. OF THOSE IMAGES WHICH ARE PRESENTED TO OUR EYES IN MIRRORS.

Empedocles says that these images are caused by certain effluxes which,
meeting together and resting upon the superficies of the mirror, are
perfected by that fiery element emitted by the said mirror, which
transforms withal the air that surrounds it. Democritus and Epicurus,
that the specular appearances are made by the subsistence of the images
which flow from our eyes; these fall upon the mirror and remain, while
the light returns to the eye. The followers of Pythagoras explain it by
the reflection of the sight; for our sight being extended (as it were)
to the brass, and meeting with the smooth dense surface thereof it is
forced back, and caused to return upon itself: the same takes place in
the hand, when it is stretched out and then brought back again to the
shoulder. Any one may use these instances to explain the manner of
seeing.

CHAPTER XV. WHETHER DARKNESS CAN BE VISIBLE TO US.

The Stoics say that darkness is seen by us, for out of our eyes there
issues out some light into it; and our eyes do not impose upon us, for
they really perceive there is darkness. Chrysippus says that we see
darkness by the striking of the intermediate air; for the visual spirits
which proceed from the principal part of the soul and reach to the ball
of the eye pierce this air, which, after they have made those strokes
upon it, extend conically on the surrounding air, where this is
homogeneous in quality. For from the eyes those