COLOR VISION 881 



pasteboard. The latter are slit radially from periphery to center so 

 that they may be lapped over each other to expose a larger or smaller 

 segment of each. Another method is to superimpose different sections 

 of the spectrum upon a screen by means of a system of lenses or mir- 

 rors. In either case, this physiological mixing of colors cannot be com- 

 pared with that employed by the painter. Thus, a blue and yellow 

 pigment when mixed, give rise to the sensation of green and not of 

 white, because these two colors combined absorb all the rays excepting 

 the green, the latter only being reflected into the eye. When used 

 alone, the former appears blue, because it allows only the blue and 

 some of the green rays to be reflected, while the latter appears yellow 

 because it absorbs all the rays excepting the yellow. Consequently, 

 when we mix these colors we obtain a subtraction, the blue pigment 



FIG. 480. ROTHE'S ROTATORY APPARATUS FOR COLOR Discs. IT is so ARRANGED AS TO 

 GIVE VARIOUS RATES OF ROTATION BY COMBINING THE MOTIONS OF 1, 2, AND 3. 



absorbing the red rays which the yellow pigment lets pass, while the 

 yellow pigment absorbs the blue rays which the blue allows to pass. 

 Thus, only the green rays are left over. 



The colors which may be arranged in a series of pairs to give white 

 are the following: 



Wave-lengths. 



Red and greenish blue 656-492 



Orange and blue 608-490 



Bright yellow and blue 574-482 



Yellow and indigo 567-465 



Greenish yellow and violet 564-433 



The fusion of a pair of colors lying closer together than their com- 

 plementary colors, yields an intermediate color which becomes more 

 completely saturated or free from white, the nearer they are to one 

 another. Thus, the union of red and yellow gives rise to orange, 

 but the latter is less saturated than the corresponding spectral color. 

 In the former instances, for example, rays of 656 juju and 564 /z/x are 



56 



