Page:Mind (Old Series) Volume 12.djvu/349

 336 w. JAMES : The judgment of objective singleness and that of identical direction seem to hang necessarily together. And that of identical direction seems to carry with it the necessity of a common origin, between the eyes or elsewhere, from which all the directions felt may seem to be estimated. This is why the cyclopean eye is really a fundamental part of the formulation of the theory of identical retinal points, and why Hering, the greatest champion of this theory, lays so much stress upon it. It is an immediate consequence of the law of identical projection of images on geometrically similar points that images which fall upon geometrically disparate points of the two retinae should be projected in disparate directions and that their objects should consequently appear in two places or double. Take the parallel rays from a star falling upon two eyes which converge upon a near object O, instead of being parallel, as in the previously instanced case. If SL and SB in Fig. 2 be the parallel rays, each of them will fall upon the nasal half of the retina which it strikes. But the two nasal halves are disparate, geometrically symmetrical, not geometrically similar. The image on the left one will therefore appear as if lying in a direction left- ward of the cyclopean eye's line of sight ; the image of the right one will appear far to the right of the same direction.