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 reproducing filters, i.e., they transmit or reflect those portions of the spectrum which the latter absorb, and vice versa.

B. .—There are now available several notable systems of reflection color. standards (). Those which are best known to American workers are the (') designed for use by artists and the  (') intended for the ornithologists. More recently Ostwald ('; ') in Germany has published an elaborate scheme of this sort. Each of these systems comprises pigments of various selective and total reflection spaced fairly evenly over the total field of possible pigment colors.

(a) The Munsell System is based upon ten hues and nine degrees of “value,” or of light reflecting power. Each of the hues is represented at each level of reflectivity by as many different saturation steps as is feasible. The system as published includes a text on “Color Notation,”(') an atlas, (') and a color sphere, as well as cards embodying the separate pigment values. Priest and his associates () have determined the spectral reflection curves of representative members of the pigment system, and have made recommendations for its improvement, although in general commending it as it stands. Evaluations of certain Munsell colors in terms of elementary sensations are given in the next Part of the present Report. For the spectral reflections reference should be had to Priest’s original paper.

(b) The Ridgway System utilizes thirty-six hues, having approximately equal spacing on the spectral chroma scale, each of these being diluted with white in three degrees and with black in three degrees, making 1115 colors in all. Jones () has made careful monochromatic analyses of the undiluted colors, and has determined the separations of their dominant hues on the hue scale, the average for the spectral hues being 3.5 and for the purples 4.4 just noticeable steps. Considering the practical difficulties encountered in the preparation and reproduction of pigment samples the gradation of values exhibits excellent uniformity. The results of Jones’ analyses are given in. Spectrophotometric measurements on the Ridgway pigments