OP ARTS AND SCIENCES. 407 



These unexplained flicts, however, are very simply accounted for, vpheu 

 we reflect on the instability which the central position of the green 

 disks would give them, and the readiness with which a wave of disturb- 

 ance, starting here and passing each way, would produce the impression 

 of an admixture of white light ; while the abruptness with which the 

 impression of green fades out, after the stimulus ceases, leads us to 

 believe, according to tlie law of acoustic sensibility in sonorous bodies, 

 that the green disks give sympatJietic response to a greater variety of 

 wave-lengths than the red, or even the violet ; in other words, that the 

 sympathetic function at the centre of the cone-spectrum is less special- 

 ized than at its ends. This, too, if rays are brought to a second focus 

 in each cone, we should expect. 



Passing to violet, we must believe that the retina is directly sensitive 

 to its own fluorescence. This, Helmholtz says, is improbable. But, if 

 fluorescence is a property of the anterior layers of the retina, why 

 should the eye not be sensitive to it, as it is to the retinal blood-vessels, 

 or to the almost constant stimulation of blood-color from other adjacent 

 membranes ? If, on the other hand, the light green which has been 

 observed in a fresh retina, under the stimulation of ultra violet rays, is 

 due to a complementary activity of the green disks, then, of course, 

 the mind perceives it directly in the lavender gray which may be seen 

 by a- sensitive eye among the most refrangible rays. Of course, this 

 question is greatly complicated by the fact that the lens is far more 

 fluorescent, and scatters light blue rays all over the interior eye ; and 

 that even the cornea and vitreous humor aid in this general dispersion. 

 While this would impair the distinctness of every violet image, it does 

 not seem sufficient, without adding the eff'ects of retinal fluorescence, to 

 account for the evanescent touch of green which appears in ultra violet 

 rays. It is possible, though hardly probable, that retinal fluorescence 

 is a part of the function by which complementary colors are developed. 



Before the late observations of Boll and Kiihne, the theory that 

 colors are to any extent reproduced in the eye would have been thought 

 as baseless as the scholastic doctrine of visible species, or the Cartesian 

 theory that colors are different rates of vortical motion. Boll now, 

 however, not only insists that we must choose between what he terms 

 the interpretation and the identity theories, but gives his vote for the 

 latter. The great interest which the psychologist feels in these inves- 

 tigations is because this question is at least involved here. While it 

 would be premature to say that all the observations thus far can be 

 interpreted upon the hypothesis of a cone-spectrum, it seems quite cer- 

 tain that they cannot be interpreted in accordance with Young's theory. 



