QUALITIES
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ments, but the fact is a new one to many persons, since the training of the color sense has been left so much to guess-work and personal whim that the thought of testing these vagaries is resented as inartistic, mechanical, and even unwise, and the suggestion of written color seems preposterous. Only a few centuries have passed since Pope Gregory's friend said, “Unless musical sounds be retained in the memory, they perish, for they cannot be written”; yet musical intervals are now accurately measured and written, and the time may not be far distant when the sensations of value and chroma will be defined and recorded with equal ease. The chroma of the spectrum is nearly equal through-out, but it is a great mistake to assume the same of pigments. In fact, the best blue-green is but half the chroma of vermilion red; and this becomes evident the moment they are tested by proper instruments. To portray this unbalance, the strongest hues must project unevenly beyond a spherical surface, as shown in the appendix to this chapter.
(33) For this reason the color tree is a completer model than the sphere, although the simplicity of the latter makes it best for a child’s comprehension.
(34) The color tree is made by taking the vertical axis of the sphere, which carries a scale of value, for the trunk. The branches are at right angles to the trunk; and, as in the sphere, they carry the scale of chroma. Colored balls on the branches tell their Hue. In order to show the maxima of color, each branch is attached to the trunk (or neutral axis) at a level demanded by its value,—the yellow nearest white at the top, then the green, red, blue, and purple branches, approaching black in the order of their lower values. It will be remembered that the chroma of the sphere ceased with 5 at the equator. The color tree pro-
