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spectral distribution. Other methods accomplish this result in terms of a complex stimulus, having general characteristics varying with the method, but seldom spectrally identical with the stimulus to be measured, which nevertheless is found empirically

Fig. 9
Triangle, Showing Loci for Various Monochromatic Analyses
(The ordinates give the percentage excitation values for Red and the abscissae those for: Violet.)

to evoke the same color as the latter. The most important of these methods which depend upon simple color matching are as follows.

B. Monocuromatic Analysis.—In this method the variable stimulus is composed of heterogeneous radiation, which by itself evokes white or gray, combined with homogeneous radiation of variable wave-length. The total intensity, ratio of homogeneous