604 



SCIENCE. 



[N. S, Vol. VII. No. 174. 



to take up the former metaphor again, show 

 him the competing theories in their right per- 

 spective. 



It may be said, without any hesitation, that 

 there are now only two discussable theories of 

 Color Vision, those of Helmholtz and of Her- 

 ing. The theories of Konig, von Kries and 

 Mrs. Ladd Franklin are simply improvements 

 on (or modifications of) the ' tri-component ' 

 theory of Helmholtz. The theories of G. E. 

 Miiller and of Ebbinghaus stand in a like rela- 

 tion to the ' antagonistic color ' theory of Her- 

 ing. I will say a few words upon both the- 

 ories. 



I. The Helmholtz theory. — This theory was 

 devised to explain ' the phenomena of color 

 mixture and color analysis '. (Stevens, p. 520). 

 It does explain them, admirably ; it explains 

 nothing else. It breaks down in face of the 

 facts of color blindness, of indirect vision, of 

 after-images and contrast, of the Purkinje 

 phenomenon, etc. Hence, its original and 

 most attractive simplicity (p. 516) has been 

 given up in favor of Konig's shift of excita- 

 bility in the three elementary substances, von 

 Kries' double white-process (one-flbre white 

 and three-fibre white), and Mrs. Ladd Frank- 

 lin's hypothetical molecule of suicidal tendency. 

 All these modifications are of the nature of 

 subsidiary or ' bolstering ' hypotheses ; each of 

 them has had grave experimental objection 

 urged against it. 



II. The Hering theory. — "The Hering hy- 

 pothesis," says Professor Stevens, "is well 

 known and probably universally rejected among 

 physicists." The latter part of this statement 

 I believe to be substantially true ; the first half 

 I must take leave to doubt. Hering's theory 

 in its modern form has nowhere received com- 

 plete exposition. Indeed, if Professor Stevens 

 has not, in the course of his psychological 

 reading, come upon Ebbinghaus' theory, 

 which is readily accessible in a recent volume 

 of the Zeitschrijt fur Psychologic, the conclu- 

 sion is almost forced upon one that he has not 

 himself followed up the Hering theory in its 

 meanderings through a large number of scat- 

 tered journals, some of which are now not 

 at all easy to procure. A brief account of 

 my own experience may, perhaps, serve to 



justify the bluntness of this remark. Until re- 

 cently there was one weak point in the Hering 

 theory which absolutely forbade its acceptance 

 by the psychologist. Having satisfied myself 

 that this defect was really fatal to the theory, 

 I was content for several years to know only 

 the general accounts of it given, e. g., in Helm- 

 holtz's Opiik, Wundt's Physiologische Psychologie, 

 Hermann's Sandbuch, Hering's own Zur Lehre 

 vom Lichtsinn, etc. Not till the publication of 

 Miiller's article, which removed the difiiculty, 

 did I make any serious effort to gain a thorough 

 understanding of Hering's point of view. 

 And if the psychologist is thus remiss, what 

 can be expected of the physicist ? 



Hering's theory is, in actual fact, every whit 

 as adequate to the phenomena of color mixture 

 as is that of Helmholtz. It also oSers a self- 

 consistent explanation of the other phenomena 

 referred to above. It has, further, on more 

 than one occasion, been led to predict a certain 

 state of sensitivity or sensible discrimination, 

 and its predictions have been verified. I do not 

 know what more can be demanded of a psycho- 

 logical theory. The objection to it was that 

 the concept of antagonism was used in one 

 sense for red-green and blue-yellow, and in an- 

 other, quite diflerent sense, for black-white ; 

 but MUller has demonstrated that the black- 

 white antithesis may be of precisely the same 

 nature as the other two, despite the existence 

 of the sensation gray. Ebbinghaus' theory 

 (which is, by the way, a model of expository 

 method) attempts to find an anatomical sub- 

 strate for the three visual substances of the 

 ' antagonistic color ' theory. 



I have so far said nothing of Wundt's theory. 

 This, the periodicity theory, did not, of course, 

 originate in the Philosophische Studien article to 

 which Professor Stevens refers ; it antedates 

 Hering's Zur Lehre, etc. (see Phys. Psych., 1874, 

 p. 388 ; 1880, p. 452). It arose by way of re- 

 action against Helmholtz, and has the merit of 

 possessing an independent white-process. But, 

 though it covers all the facts, it covers them too 

 loosely to serve as a genuine working hypoth- 

 esis. Hence it has never succeeded in get- 

 ting itself discussed. It was an excellent make- 

 shift so long as definite factual objections 

 could be urged against Helmholtz and Hering 



