Book 4
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DEMOCRITUS and Epicurus suppose that sight is caused by the insinuation of little images into the visive organ, and by the entrance of certain rays which return to the eye after striking upon 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 congruous air, and there is likewise a light emitted from bodies, which meets and is joined with the fiery visual light in the intermediate air (which is liquid and mutable); and the conjunction 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.
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EMPEDOCLES says that these images are caused by certain effluvias which, meeting together and insisting upon the superficies of the mirror, are perfected by that fiery quality emitted by the said mirror, which transmutes withal the air that surrounds it. Democritus and Epicurus, that the specular appearances are formed by the subsistence of the images which flow from our eyes; these fall upon the mirror and remain, while the light rebounds 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 struck back, and caused to return upon itself: the same appears in the hand, when it is stretched out and then brought back again to the shoulder. Any one may apply these instances to explain the manner of seeing.
Chapter XV. WHETHER DARKNESS CAN BE VISIBLE TO US.
