bodies; I therefore now see two objects, precisely because perception takes place by means of, and within, the Understanding.—The same thing happens without squinting when, for instance, I look fixedly at the furthest of two objects placed at unequal distances before me, and complete the optic angle at it; for then the rays emanating from the nearer object do not impinge upon symmetrically corresponding places in both retinas, wherefore my Understanding attributes them to two objects, i.e. I see the nearer object double (see fig. 2, page 70). If, on the contrary, I complete the optic angle at the nearer object, by looking steadily at it, the further object appears double. It is easy to test this by holding a pencil two feet from the eyes, and looking alternately at it and at some other more distant object behind it.
But the finest thing of all is, that this experiment may quite well be reversed: so that, with two real objects straight before and close to us, and with our eyes wide open, we nevertheless see but one. This is the most striking proof that perception is a work of the Understanding and by no means contained in sensation. Let two cardboard tubes, about 8 inches long and 1½ inches in diameter, be fastened parallel to one another, like those of a binocular telescope, and fix a shilling at the end of each tube. On applying our eyes to the opposite extremity and looking through the tubes, we shall see only one shilling surrounded by 'one tube. For in this case the eyes being forced into a completely parallel position, the rays emanating from the coins impinge exactly upon the centres of the two retinas and those points which immediately surround them, therefore upon places which correspond symmetrically to each other; consequently the Understanding, taking for granted the usual convergent position of the optic axes when objects are near, admits but one object as the cause of the reflected rays. In other words, we see but
