September 14, 1900.] 



SCIENCE. 



409 



absolutely do consciousness as to which eye we 

 are seeing anything with. 



It is customary to speak of color-mixing as 

 if it were the same sort of thing throughout the 

 whole spectrum, but in reality it is of two very 

 different kinds. When a unitary green and 

 blue are mixed to produce a blue-green, the 

 phenomenon is purely a psychological one (and 

 there is nothing strange in the fact that such 

 mixtures work binocularly as well as monocu- 

 larly) ; we can see in the blue-green the blue 

 and the green of which it is composed (and we 

 have not even in this case taken the trouble to 

 devise a separate name for it). But if a spec- 

 tral red and a spectral green in neither of 

 which any trace of yellow can be detected be 

 seen together (and even if one of them is a 

 trifle bluish), a yellow is produced which has 

 not any perceptible falling oflF, even in satura- 

 tion, from the yellow of the spectrum (as has 

 just been stated explicitly by Breuer and von 

 Kries); and a correspondingly strange event 

 results from the mixing of blue and yellow. To 

 say that such a transformation-scene as this is 

 the work of judgment (the judgment being led 

 to it by no motive whatever — it cannot be any- 

 thing in reality, it would seem, but the pure 

 spontaneous play of fancy, rather than the work 

 of a reasons-obeying judgment, or perception) — 

 this is to make a serious draft upon the powers 

 with which we need to endue that faculty, or, to 

 use the more modern term, that cortical center. 

 At all events, the two occurrences are very dif- 

 ferent, and my object now is merely to suggest 

 that they should be called by different names. 

 When green and yellow producing ether-radia- 

 tions are thrown together upon the retina, I 

 would propose that the yellow-green sensation 

 which results, be called a color-blend, and that 

 the two colors be said to be blended. But when 

 yellow and blue unite to make gray, I should 

 say, using in fact a term of Helmholtz's, that 

 the process is one of mutual color- quenching 

 (and in the same way red and green may be 

 said to quench each other when they result in 

 yellow). Color-blending is plainly a psycho- 

 logical matter ; color-quenching it is far more 

 natural, in the first instance, to attribute to a 

 peculiarity of the photo-chemical processes 

 which we know to be going on in the retina. 



Farther — still in the interest of mutual com- 

 prehensibility between the adherents of different 

 schools, who speak at present languages which 

 have too little in common — I would propose to 

 call red, yellow, blue, and green, not primary, 

 nor elementary, nor fundamental colors — that 

 commits one to one or other of the rival 

 schools ; not ' principal ' colors — that is purely 

 an aesthetic designation ; but unitary colors. 

 Since the admirable discussion of this subject 

 by Professor Ellas Miiller {Ztsch. f. Psychol., 

 Vols. X. and XIV.) no one can doubt — even of 

 those who doubted it before — that these partic- 

 ular ether-radiations have for consciousness a 

 peculiar character — that of being the end-mem- 

 bers of ' rectilinear ' color-series (series such 

 that each member differs from the one before 

 it in the same way in which that differs from 

 the one next preceding); in other words, they 

 are not, for consciousness, of the nature of 

 color-blends. Yellow-green and green-blue are 

 — on their faces — color- blends. Orange and 

 violet have secured unitary names for them- 

 selves (though they are nothing but a reddish 

 yellow and a reddish blue) — doubtless on ac- 

 count of the excessive interest which attaches to 

 reds in nature as compared with greens; but that 

 is not sufiBcient to make them unitary colors. 

 This nomenclature commits one to no theory 

 whatever — whether retinal or cortical ; it is 

 simply the expression of the psychological fact 

 that there are four very characteristic points in 

 the color gamut, red, yellow, green and blue, 

 their character being sufliciently described by 

 the word unitary. That this is true will easily 

 be seen by any one who will take the trouble 

 to spread out for himself in order in a circle as 

 many different color-hues (all of the same satu- 

 ration and the same brightness — the spectrum 

 will not do, therefore), as can be procured. 



To conclude, a color-blend is then surely a 

 psychological product ; an instance of color- 

 quenching is either psychical or physiological 

 according to the theory which one is pleased to 

 adopt. How hard it is for the physicists to 

 understand this point of view is evidenced by 

 the fact that they are constantly affirming that 

 fresh proof has been adduced of the Young- 

 Helmholtz theory, because it has been shown 

 that all the colors of the rainbow and white 



