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 by this measured system, which in a few weeks lost four steps of chroma, gained two steps of value, and swung into a bluer hue.

(101) But the color sphere to be next described is worked out with a few reliable pigments, mostly natural earths, whose fading is a matter of years and so slight as to be almost imperceptible. Besides, its principal hues are preserved in safe keeping by imperishable enamels, which can be used to correct any tendency of the pigments to distort the measured intervals of the color sphere.

This meets the most serious objection to a pigment system. Without it a child has nothing tangible which he can keep in constant view to imitate and memorize. With it he builds up a mental image of measured relations that describe every color in nature, including the fleeting hues of the rainbow, although they appear but for a moment at rare intervals. Finally, it furnishes a simple notation which records every color sensation by letters and numerals. With the enlargement of his mental power he will unite these in a comprehensive grasp of the larger relations of color.