SENSE ORGANS. 



137 



Brewster wrong, for pigments are never pure colors. A 

 mixture of blue and yellow pigments makes green, be- 

 cause both of the components contain some green ; and 

 when they are mixed, the yellow and blue kill one 

 another, and the green of both comes out. 



Hering differs from both the preceding. He makes 

 six primary colors — viz., white, black, red, yellow, green, 

 and blue. Furthermore, according to him, these con- 

 stitute three pairs of complementaries — viz., white and 

 black, red and green, yellow and blue. There is but one 

 objection that can be made to Hering's view — viz., his 

 inclusion of white and black. These should be put into 

 a different category — viz., that of shade instead of color, 

 of intensity or quantity instead of quality. Leaving out 

 these, Hering's four colors, or two pairs of complemen- 

 taries, are red and green, yellow and blue. Undoubt- 

 edly from the point of view of sensation, unplagued by 

 any physical considerations, Hering is right. As color- 

 sensations these are perfectly simple and wholly distinct, 

 and this is true of no other colors. Scarlet and orange 

 are plainly and visibly a mixture of red and yellow, 

 purple a mixture of blue and red, and even violet is a 

 blue with a glow of red. White and black are also in- 

 deed pure simple sensations as Hering maintains, but 

 color is not the proper word to express these sensations. 



Theory of Color Perception ; General Theory. 

 — 1. Color is a simple sensation and incapable of analy- 

 sis into any simpler elements. It must be, therefore, 

 the result of retinal structure. 2. It is an endowment 

 of the cones and not of the rods. This is shown by the 

 fact that the distribution of color perception over the 

 surface of the retina is identical with the distribution 

 in number and fineness of the cones. In the fovea there 

 is nothing but cones, and these are very small, and the 

 color perception is therefore keenest at the point of 



