408 



SCIENCE. 



[N. S. Vol. XII. No. 298. 



specialization, in pronouncing upon a critical 

 question in the classification of the fossiliferous 



rocks. 



John M. Clakke. 



the problem dp color. 

 Although I don't accept Professor Cattell's 

 contention, in the last numher of the Psycholog- 

 ical Review, that the nugatory process by which 

 two colored lights (if properly chosen in hue 

 and in intensity) disappear for sensation and 

 leave behind a sense of grayness only is due to 

 a cortical and not to a retinal physiological 

 process, I am nevertheless willing (in the in- 

 terest of fair play) to furnish him with one 

 more reason on his side. When a colored ob- 

 ject is mirrored in a piece of colored glass 

 (say red in blue), we get in general a color blend, 

 that is, for consciousness, a reddish-blue sensa- 

 tion. In case the colors chosen are a pair 

 which, on fusing, are transformed into some- 

 thing else (yellow and blue into white, or red 

 and green into yellow), this is, according to all 

 the non-psychical color-theories, because two 

 counteracting color-processes in the retina are 

 exactly balanced, or else because two partial 

 photo-chemical molecular dissociations unite to 

 complete each other and to produce an un- 

 differentiated gray- process, — either of these 

 suppositions being sufficiently plausible in 

 itself. But — and this is the fact, if it is a fact, 

 which works upon Professor Cattell's side — 

 there are occasions upon which, according to 

 Helmholtz and to Wundt, this antagonism, or 

 this completion, fails to take place. One some- 

 times sees, they say, one color through the 

 other ; guided by the belief that the red sensa- 

 tion is due to the presence of a red book, e. g., 

 one cannot help but see the redness of the book 

 through the sea of blue. They do not dwell 

 upon the colors which they used in making the 

 experiment — so long as these are red and blue 

 there is nothing strange in the differing inter- 

 pretations ; but if, under these circumstances, 

 blue and yellow should not give white (and red 

 and green should not give yellow), then it 

 would seem to follow that the antagonistic or 

 the completing processes are not of the nature 

 of chemical changes in the retina — such could 

 not be so easily undone by the reasoning, or the 



perceiving. Psyche. Hering denies with great 

 warmth the contention of Helmholtz and of 

 Wundt that these exceptional cases occur ; or 

 rather, he says that if they do occur it is owing 

 to spots or unevennesses in one or the other of 

 the two surfaces. But even though she be as- 

 sisted by any ulterior aids whatever, it would 

 not seem that the Psyche can undo, in the in- 

 terests of reasonable interpretation, a chemical 

 change that has already taken place. Perhaps 

 she can, however; but in that case her powers 

 must also suffice to undo an actual white (or yel- 

 low) an d separate it into its possible components. 

 If, in the case of a blue book seen in a yellow 

 glass, for a portion in the center of the surface 

 of the book a gray of equal brightness be sub- 

 stituted, and alike gray for an exactly coincid- 

 ing portion of the yellow reflector, then it is 

 possible that self-deception would go so far as to 

 enable us to see a continuous blue book in a 

 continuous yellow mirror. The experiment is 

 perhaps worth trying. 



On the other hand (to be equally fair to my 

 own side, in turn), the fact that binocular color 

 mixture does not occur to any great extent — 

 that is, does not occur for colors far apart in 

 the spectrum — is at once destructive to any 

 hypothesis which relegates the fusion of colors 

 to the perception-forming centers of the brain. 

 Whether an overlapping blue and yellow are 

 mediated by one eye or by two can have nothing 

 to do with the case if their mutual quenching 

 is an affair of perception. Helmholtz, after a 

 long series of the most painstaking experiments, 

 declared absolutely that binocular color-fusion 

 does not take place.* This shows, in passing, 

 the unprejudiced character of his work, for the 

 fact, as I have said, is quite destructive to his 

 theory that the mutual suppression of blue and 

 yellow into white is merely a matter of the 

 judgment : it cannot make any difference 

 whether we know that we see blue and yel- 

 low at once through one nasal half-retina, or 

 through a nasal and a temporal half-retina to- 

 gether — the more so as we have in 



* Binocular color-fusing of two complementary 

 colors many be obtained with the Hering color-mixer 

 by ' long and steady gazing, ' but this is the sufficient 

 condition for turning each color into a dead gray, 

 when looked at by itself. 



