1876.] ALo [Hartshorn e. 



problem of the Vision of colors; which, as the great German physicist de- 

 clares, had baffled not only the powerful mind of the poet-philosopher 

 Goethe, but many able students of pliysics and physiology besides. 



There seems to be no good reason for hesitating to accept this theory, of 

 the special responsiveness of certain retinal nerve-elements to particular 

 luminous rays. Helmholtz supports it by at least one striking fact in the 

 comparative histology of the eye; viz: that in a number of birds and reptiles, 

 many of the rods of the retina contain, at their ends which are turned 

 towards the light, minute drops of colored oil; in some red, in others yellow; 

 while others of the rods in the same eyes are entirely colorless. Also, he 

 refers to the analogy of the organs of Corti in the cochlea of the ear; which 

 are supposed, with considerable reason, to vibrate in accordance with par- 

 ticular notes of sound; and, also, to some remarkable external filamentous 

 appendages to the organ of hearing in certain marine crustaceans; which 

 Hensen, of Kiel, has shown to be set in motion, some by one, and some by 

 other kinds of sonorous vibration. These last facts recall the admirable 

 and similar series of experiments of Prof Mayer, upon the vibrations of 

 the antennae of mosquitoes. I believe that there is much importance in 

 this general theory of undulatory consonance, and of special responsiveness, 

 of the minute elements of the organs of sense. It is in the manner of the 

 application of this theory by Helmholtz, and, with him, by all other late 

 physiological writers known to me, to the explanation of negative and com- 

 plementary color spectra, and color shadows, that it appears to me a defi- 

 ciency exists, fatal to the reception of that current explanation ; and suggest- 

 ing, if not proving, an almost or quite contrary view of the same facts. 



The application I here mean to object to, is this: that negative and com- 

 plementary color spectra and color shadows are all explained by partial 

 or local fatigue of the retina, under impressions of light, so that the part 

 of the retina impressed, e. g., by a particular color, becomes, through 

 fatigue, less sensitive to the same color, kind, or degree of light; and 

 therefore an impression is, during the time of that fatigue, made upon our 

 visual consciousness only by the opposite or complementary rays; these 

 affecting those parts or elements of the retina which are fresh, not having 

 been wearied by use. According to this, when we look for a time upon 

 a red object, those rods and cones, or nerve-cells, or nerve-filaments (or, 

 as Prof Draper would have it, portions of the choroid coat behi?id the 

 retina) which are affected by red rays, become exhausted; and so, when 

 we turn toward a white ground, we are, for the time, red-blind; while the 

 green-seeing capacity, so to speak, is fresh and vigorous. Thus we see, at 

 that time, only green; or, the complementary color in any other like case. 

 This fatigue theory is what I am constrained, notwithstanding the very 

 eminent authorities by whom it has been hitherto supported, to call 

 definitely in question. Let me here mention the observations which first 

 led me to look for a different view of the whole subject of these kindred 

 phenomena. 



If a piece of thin white paper, such as is commonly used, on account of 



