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 point in question, the proportions being determined again by the “center of gravity” principle, applied to the segments of the line thus established. There are obviously an infinite number of such mixtures, not only of two components but of any number of components.

It is one of the functions of the present Report to provide the excitation values of characteristic stimuli, computed by the method outlined above. Tables of such values, for black body colors, colors obtained by rotatory dispersion, Munsell colors, etc., will be found below in conjunction with the discussion of the excitation equivalents of these various standards.

B. .—The general principles underlying the reduction of monochromatic analysis specifications to color excitation values are similar to those outlined above, but with certain complexities which are introduced by the use of a photometric method for establishing and expressing the ratio between the amounts of “white” and monochromatic stimulus in any given case. It is of course natural in practice to specify this ratio in luminosity terms, but these terms play no part in determining the excitation values given in. Consequently, in order to effect the requisite transformation, it is necessary to make use of the luminosity valencies of the several excitations, which were discussed on. To simplify computation, these valences have been expressed so as to represent the fractional contributions of the three excitations to the luminosity of a white, taken as unity, the values being: for the red 0.370, for the green 0.617, and for the blue 0.012.

The actual steps which are involved may be outlined as follows. (a) It is first necessary to know the spectral distribution of radiant intensities for the stimulus which is employed as a white in the given measurements. In case the distribution in question is that of average noon sunlight—or a distribution which color-matches this—it is only necessary to multiply each of the luminosity valences above considered, by the “per cent. white” of the specification. If, on the other hand, the “white” departs in effective character from average noon sunlight, excitation values must be computed for it by the method described under