406 PROCEEDINGS OF THE AMERICAN ACADEMY 



that the two change their relative position with every irritiition, we 

 should expect tliat the ends of the cones would be often injured or un- 

 developed, as, indeed, the microscopist often finds them. How far the 

 insensibility of the normal eye to the less refrangible red rays is due 

 to the limit of retinal function, and how far to the absorptive power of 

 the lens and humors, has never been determined. We should expect, 

 however, to find some of the thermal rays just at or beyond the point 

 of the external cone, perhaps limiting, and sometimes even impairing, 

 its functions. Toward the violet end of the spectrum, there is good 

 reason to believe that no solar rays enter our atmosphere which do not 

 cause, at least, fluorescent sensibility in the retina. 



Professor Fick has lately reinvestigated the facts of the color- 

 blindness of the equatorial tracts of the retina, and frankly admits 

 that the phenomena he has observed cannot be explained by the ab- 

 sence of a fundamental color. He endeavors, however, to preserve the 

 hypothesis of three sets of fibres by arguing that the 2>hysical con- 

 stitution of the eye is such that excitation must be considered as a 

 function of oscillation. Thus, the longer ordinates of the curves rep- 

 resenting the maxima of each of the three sensations in the spectral 

 series of colors approach each other as the color-blindness here becomes 

 complete, or as the angle of vision increases : so that, e. g., a red ray, 

 falling here, might appear yellow. Now, by assuming near the ora ser- 

 rata either a shortening or an inclination of the cones, so that either 

 the red disks are absent, or not reached by their corresponding rays, 

 these phenomena, if we take into account the chromatic aberration of 

 the ante-retinal eye, which Fick has entirely disregarded, can all be 

 explained in a much simpler way. More accurate observations, how- 

 ever, than have yet been recorded, respecting tlie angle of inclination 

 of the ray to the cone, and the amount and uniformity of shortening of 

 the external cone near the front edge of the retina, are here needed. 



The peculiar relation of green to the two other colors, as shown on 

 the leverage curve, or chart of mixing, as reconstructed by Maxwell, 

 has never been satisftictorily explained on the hypothesis of Young. 

 Why have we here a curve, and not an angle, as at red and violet ? or, 

 in other words, why does the mixture of any two tones of green cause 

 such a sudden and exceptional decrease in saturation ? 



When we consider the almost perfect integrity with which the green 

 rays reach the retina, and its sensitiveness to them, we should expect 

 not only a greater saturation than is observed in the spectrum, but also 

 moi'e shades and more distinct hues than we find upon the color table. 

 The complementary hues of green are numerous and pronounced. 



