544 VISION 



In the preceding table have been brought together after Helmholtz the results 

 of mixing different spectral colors. At the top of the vertical columns and at 

 the left are found the simple colors; where the vertical and horizontal columns 

 intersect are found the colors resulting from the mixture of the two simple 

 colors standing at the beginning of the intersecting columns. 



D. ON THE THEORY OF COLOR 



From the facts just given it appears that we can produce the whole series 

 of different color tones by appropriate mixture of a few simple colors. Any 

 physiological theory of color has therefore to show what these simple colors 

 are and to derive all color sensations from them. 



There are at this time two principal opposing views as to the production 

 of color, namely, the three-color theory, originally proposed by Thomas Young 



R O Y G B V 



FIG. 237. Excitation of the different components of the visual organ by light rays of different 



wave lengths, after Helmholtz. 



and later developed by Helmholtz, and the theory of antagonistic colors, 

 offered by Hering. Since an exhaustive critical discussion of these views 

 would call for entirely too much room and inasmuch as it will probably be 

 a long time yet before the question is finally settled, we shall limit the dis- 

 cussion to a purely dogmatic statement of the essence of the two theories. 



1. The Three-color Theory. Young regarded red., green and violet as 

 fundamental or primary colors, because they cannot be obtained, at least not 

 in complete saturation, by mixture of other colors. He supposed that in every 

 part of the retina which is capable of all the color sensations, there are three 

 separate nerve elements: stimulation of the first produces the sensation of 

 red; stimulation of the second, that of green; stimulation of the third the 

 sensation of violet. Since the action of light on the percipient parts of 

 the retina is in all probability a chemical process in which certain com- 

 pounds are broken down, there would be in the retina, according to this 

 theory, three different visual substances corresponding to the three primary 

 colors. In order not to commit ourselves as to the way in which the light 

 acts directly, we shall designate these percipient elements in general as com- 

 ponents of the visual organ. 



Light acts with varying intensity according to its wave lengths, on the 

 three components. The red-perceiving component is excited most powerfully 

 by light of the greatest wave length; the green-perceiving component by 

 light of medium wave length, and the violet-perceiving by light of the shortest 

 wave length. However, it is possible, and for the explanation of certain phe- 

 nomena it is necessary, to assume that each spectral color stimulates all the 

 components, one of them feebly, the others powerfully. 



