588 



THE NERVOUS SYSTEM. 



table are given the wave-lengths for the center of each color in 

 ten-millionths of a millimeter. 



Red 7000 



Orange 5972 



Yellow 5808 



Green . 5271 



Blue . . ...'.>- 4960 



Indigo 4383 



Violet . . 4059 



There are rays, calorific rays, beyond the red rays whose wave- 

 lengths are longer than the red, and others beyond the violet whose 

 wave-lengths are shorter than those of the violet ; these latter are 

 the actinic rays ; neither the calorific nor the actinic rays are visi- 

 ble. 



If, after the dispersion, a second prism in reversed position 

 (Fig. 363) is placed in the path of the colored rays, these will be 



FIG. 363. Reunion of colored rays to form white light. 



reunited, and will emerge from the second prism as white light. 

 This synthesis of light, or the composition of white light by the 

 union of all the colors of the spectrum, may be brought about by 

 the union of certain colors without using all of them ; thus red 

 and bluish green will produce white light, as will also orange and 

 light blue. Colors which when mixed produce white light are 

 complementary. In the color diagram (Fig. 364) this relation is 



FIG. 364. Color diagram. 



made evident, the form of a triangle being selected around which 

 to arrange the colors, rather than a circle, for the reason that they 

 do not act equally as stimuli. Red, green, and violet are placed 

 at the angles on the Young-Helmholtz theory of these being the 

 primary colors i. e., the theory thaf the other colors are mixtures 

 of these three colors. A reference to this diagram shows that red, 

 green, and violet, represented by R, G, and v, make white, repre- 



