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 rays are poured forth which are neither black nor cloudy. Upon this account darkness is visible to us.
CHAPTER XVI. OF HEARING.
Empedocles says that hearing is formed by the insidency of the air upon the cochlea, which it is said hangs within the ear as a bell, and is beat upon by the air. Alcmaeon, that the vacuity that is within the ear makes us to have the sense of hearing, for the air forcing a vacuum gives the sound; every inanity affords a ringing. Diogenes the air which exists in the head, being struck upon by the voice gives the hearing. Plato and his followers, the air which exists in the head being struck upon, is reflected to the principal part of the soul, and this causeth the sense of hearing.