December 12, 1913] 



SCIENCE 



851 



gets the sensation green, it is not the chloro- 

 genic light-rays (i. e., those which produce for 

 us the pure green sensation) that are achro- 

 matic to him, but that it is exactly the " blue- 

 green "-producing light-ray region to which he 

 is wholly chroma-blind. This is a hard saying 

 for the adherent of the Hering theory: one of 

 the many logical voltes-face which he is 

 obliged to perform, in order to follow his 

 leader, is to believe at one moment that red 

 and green are complementary colors (which 

 every kindergarten child knows they are not),^ 

 and to admit at the next moment that the mid- 

 spectrum region which gives an " achroma "- 

 sensation to the partially color-blind is not 

 green but blue-green. This latter fact de- 

 mands (and receives) countless most compli- 

 cated purely ad hoc hypotheses by way of 

 explanation on the part of the adherents of 

 Hering (or so many of them as have recog- 

 nized its damaging character).^ In my color 

 theory' this fact is a matter of course — it is 

 one of the facts which the theory was devised 

 for the purpose of taking account of. 



Our shockingly inadequate color-language 

 does not readily permit us to state — and hence 

 still less to remember — that objective light- 

 rays of a given periodicity are not in them- 

 selves, e. g., "green," but only a cause of a 

 green sensation, in a normal eye, after their 

 effect on the retina has been transmitted to the 

 cortex. What looks pure* green to a person 

 with normal vision will look pure yellow to 

 the partially color blind, with equal justifica- 

 tion — a fact which is quite destructive to the 



1 Hering himself has explained to me that color 

 does not mean muchj because colors vary so with 

 the illumination I 



2 See G. E. Miiller in the Zeitschrift fur Psy- 

 chologie, Bd. XIV., and passim. 



s See Baldwin 's ' ' Dictionary of Philosophy and 

 Psychology," Art. Vision, and the "Psychology" 

 of Professor Calkins, who has now relegated both 

 Helmholtz and Hering to an appendix. My theory 

 has lately been appropriated by F. Schenck. v. 

 Briicke, Zntrlb. f. Physiologie, 20, No. 23. 



* That one can perfectly well form this judg- 

 ment "imitary color," "color-blend," has lately 

 been shown by Westphal, Ztsch. f. Psychol. (1), 

 44, p. 182, 1909. 



Hering theory. We have here good proof that 

 it is important to have a reasonable color- 

 theory in the back of one's mind, or at least 

 not to have an unreasonable one. Those who 

 maintain that color-theories are, in the present 

 stage of our knowledge, of no consequence are 

 those who are nevertheless, subconsciously, 

 fully dominated by the Hering theory. They 

 will tell you, for example, that the brightness 

 of the most brilliant of reds is wholly due to 

 its whiteness, quite as if they were making, 

 not a wildly improbable theoretical statement, 

 but a plain statement of fact. One of them 

 said to me lately, " But I can not think of 

 red and green as anything but complementary 

 colors ! " No physicist, of course, can give a 

 moment's attention to a theory which flies in 

 the face of fact to this extent. On the other 

 hand, the open-mindedness to psychological 

 considerations which the physicist is sure to 

 develop some time is already evidenced in a 

 phrase lately dropped by Robert Wood (in his 

 wonderful book on " Physical Optics ") ; he 

 speaks of an even red and green light-mixture 

 as producing " subjective yellow." This is 

 probably the first time that any physicist has 

 ever found occasion to admit that though red, 

 green and blue spectral lights, if mixed, will 

 furnish matches for all the intervening colors 

 of the spectrum, it still needs to be explained 

 that the series matched by the red-greens con- 

 tains, for sensation, no trace of red-greenness. 

 Helmholtz himself said that the yellowness of 

 red-green, and the whiteness of red-green-blue 

 were quite immaterial circumstances. 



J. B. and M. L. Watson, reporting on their 

 work on the specific light response of some ro- 

 dents, in which they seemed to find that the rat 

 does not discriminate between red and green, 

 nor between blue and yellow, say : " To the ad- 

 herents of color theories the denial of a response 

 based upon wave-length, in the case of red and 

 green, and in the case of blue and yellow, is 

 the equivalent of denying the possibility of a 

 response on the basis of wave-length anywhere 

 in the animal's spectrum." But this view is 

 an indication that all theories look alike to 

 them. On my theory, which was devised for 

 the purpose of taking account of the facts of 



