. Light, a textbook for students who have had one year of physics. complementary colors. A convenient way of showing these is illustrated in figure 13. White light passes through the slit S to the lens L, which makes the rays parallel. It then passes through the prism P and the second lens L,, which focusses the spectrum in the plane vr. Instead of having a screen at this place, another lens, L3, is placed just behind it. The two lenses L2 and h3 together form an image of the face of the prism on a properly placed white screen A. Since light of all colors comes through the whole face of the pr
. Light, a textbook for students who have had one year of physics. complementary colors. A convenient way of showing these is illustrated in figure 13. White light passes through the slit S to the lens L, which makes the rays parallel. It then passes through the prism P and the second lens L,, which focusses the spectrum in the plane vr. Instead of having a screen at this place, another lens, L3, is placed just behind it. The two lenses L2 and h3 together form an image of the face of the prism on a properly placed white screen A. Since light of all colors comes through the whole face of the prism, and all the COLOR MIXTURE 25 light passes through the two lenses, this image will be uniform-ly white. Now, if an opaque obstacle be placed just in frontof L,, i. e., just in the plane in which the spectrum is formed,the obstacle being of sufficient width to cut off a certain spec-tral region, say the green, then only the remaining colors willreach the screen A, and the image of the prism-face willtherefore show the color complementary to the color cut Figure 13 By this means, we find thai the color complementary to theaverage spectral green is a peculiar shade of red, that com-plementary to spectral blue a sort of golden yellow, , one or both of a pair of complementary colors areimpure in the spectral sense. It is found that a combination of the red, the green, andthe blue of the spectrum, in suitable proportions, will producethe sensation of white, without the presence of the other colors,such as violet, orange, and yellow. This can be tried with thearrangement of figure 13 by placing before the lens L3 a cardwith holes cut through it so as to let pass only some of thesethree colors. The best exact location of the holes, and theirproper sizes, can be found only by trial. Furthermore, bysuitably altering the relative intensities of these three colors,as by stopping down one or two of the holes, any other color,ither a pure spectral hue, or such a color
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