412 PROCEEDINGS OF THE AMERICAN ACADEMY 



ceive one sixty-fourth of a semi-tone, which is less than the difference 

 between the pitch of two of Corti's arches. In the one case, the two 

 disks, as in the other the two arches, nearest attuned to the wave- 

 length, would be excited, — the nearest one the most strongly; so that 

 we shall never be able to perceive the steps or jumps which correspond 

 to the difference between the ultimate percipient elements in either the 

 tone or color scale. 



The histologist Hensen long ago conjectured that perception took 

 place at the outer segment of the cone, because the field of vision is 

 made up of points so widely separated in comparison with their diame- 

 ter. It has more recently been urged that the cones are not nervous 

 substances, and that no fibres can be found running from their external 

 segments. To this it can only be said that, if the size of the fibres 

 bears any proportion to the length of the wave, observations on the 

 ultimate nervous elements of the ear would teach us that comparatively 

 large bundles of ultimate retinal fibres would still be invisible under 

 the highest microscopic powers. The two hundred and fifty thousand 

 fibres of the oj^tic nerve may themselves be very complex. Our the- 

 ory only adds a third to the two yet unexplored intervals along the 

 diameter of the retina, which all who believe that the coues share in 

 the act of visual perception admit must be somehow traversed by sen- 

 tient processes. 



If, then, certain phenomena, like colored shadows, or the subjective 

 light of the closed eye, and many others, may be partly explained by 

 the action of disks on each other ; especially, if colors shall be found, 

 in any sense, to be reproduced on the retina, — it may be that some of 

 the many ingenious but mistaken color theories which have abounded 

 in the world ever since Plato's day may have something to teach us 

 which has been overlooked ; for instance, Schopenhauer's, wliich has at 

 least the merit of being purely physiological, while his formulce of di- 

 visible remainders, and of qualitative and quantitative retinal activity, 

 may be applied at once. 



Chodin's observation, that moderate pressure always excites a sensa- 

 tion of green, whether on a black or white ground ; Wheatstone's dis- 

 covery, that on a smooth surface of red and blue squares the red seem 

 raised ; the fact that a distant landscape, viewed with inverted head, 

 seems more like a flat surface, but more brightly colored, so that color 

 and the third dimension of space seem reciprocal functions, — these and 

 many other observations seem more or less fully explained by our hy- 

 pothesis, which at least suggests new paths of investigation, and may 

 perhaps even justify the question how much better, at this stage of our 



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