416 STUDIES IN SPECIAL SENSE PHYSIOLOGY 



more behind the steadily increasing greenishness, until we finally 

 reach a green which seems to be entirely free from' yellow. To 

 this succeed green colours which already play into blue (water- 

 green) ; further on the bluishness of the colours becomes 

 increasingly stronger, the greenishness weaker, until we finally 

 reach a blue exhibiting no more greenishness at all. To this blue 

 succeed blue colours of increasing reddishness and correspondingly 

 diminishing bluishness (blue-violet, red-violet, purple-red), until 

 the last trace of bluishness vanishes in a definite red." ( 24 ) 



If we define a pure green as a sensation free from admixture 

 with blue and yellow, and the other three sensation qualities in 

 the same manner, we see that our pure colours (from this point 

 of view) can be arranged in two pairs, yellow and blue forming 

 one and red and green the other. The members of each pair can 

 be placed opposite one another in a diagram, because we can only 

 pass from yellow to blue or from red to green by traversing the 

 province of a member of the other pair, as just explained. There 

 is no pure yellowish-blue or reddish-green sensation quality. 



But there is yet another contrast, from the standpoint of sen- 

 sation quality, between yellow and red on the one hand, blue and 

 green on the other. 



Somehow, in a manner difficult to express in words yet of 

 universal experience, the two former colours are associated with 

 a certain heightening and increased vividness of sensation-tone, 

 while the two latter exercise a depressing or subduing influence. 

 This finds its expression in the classification by artists of colours 

 into warm and cold. Goethe has emphasised these points : 



" We find from experience, again , that yellow excites a warm 

 and agreeable impression. Hence in painting it belongs to the 

 illumined and emphatic side. 



" This impression of warmth may be experienced in a very 

 lively manner if we look at a landscape through a yellow glass, 

 particularly on a grey winter's day. The eye is gladdened, the 

 heart expanded and cheered, a glow seems at once to breathe 

 towards us." () 



Of blue he says : " This colour has a peculiar and almost 

 indescribable effect on the eye. As a hue it is powerful, but it is 

 on the negative side, arid in its highest purity is, as it were, a 

 stimulating negation. Its appearance then is a kind of contra- 

 diction between excitement and repose. 



