. Refraction and motility of the eye, with chapters on color blindness and the field of vision . gment may produce very different effectsfrom mixtures of the sensations produced by those pig-ments separately. Tn dealing objectively with pigments, we find that bycombinations of the three so-called primary colors red, blueand yellow and their derivatives, we can produce all theother colors. On the other hand, in dealing with the sub-jective sensations produced by decomposed light or com- 21 322 REFRACTION AND MOTILITY OF THE EYE. paratively pure pigments, we find that by combining invarious prop
. Refraction and motility of the eye, with chapters on color blindness and the field of vision . gment may produce very different effectsfrom mixtures of the sensations produced by those pig-ments separately. Tn dealing objectively with pigments, we find that bycombinations of the three so-called primary colors red, blueand yellow and their derivatives, we can produce all theother colors. On the other hand, in dealing with the sub-jective sensations produced by decomposed light or com- 21 322 REFRACTION AND MOTILITY OF THE EYE. paratively pure pigments, we find that by combining invarious proportions the sensations produced by red, blueand green (instead of yellow) we can not only producewhite, but by varying the proportion and intensity of thethree, produce the sensation of any other color of the spec-trum. These results show that our recognized color sensa-tions may be reduced to three, that is to say, our vision istrichromic as based on variations of three primary colorsensations. When, however, we begin to investigate thephysiological processes by which we apprehend color, we. Fig. 103. JBiu.*- v>our are confronted by several rival theories: the chief beingthose of Young-Helmholtz and of Hering. We cannot gointo these theories deeply, but suffice it to say that mostfacts can be explained by both, but there are a number thatseem consistent with neither. According to the first theorythere are three sets of fibres in the retina, all of which areexcited by every color, but with different intensities. Oneof these is affected most strongly by the long waves andgives the sensation of red; another set which responds moststrongly to blue waves and a third to the green. A com-bination of waves which stimulates more than one set offibres would give a sensation of composite color according to COLOR-BLINDNESS. 323 the amount of stimulation of each as shown iii the diagram,which makes no pretense, however, of showing the exactproportions of each which cause any sensation.
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