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 a letter and two numerals. With the enlargement of his mental power he will unite these in a comprehensive grasp of the larger relations of color. APPENDIX TO CHAPTER IV. +Children’s Color Studies.+ These reproductions of children’s work are given as proof that color charm and good taste may be cultivated from the start. FIVE MIDDLE HUES are first taught by the use of special crayons, and later with water colors. They represent the equator of the color sphere (see Plate I.),--a circle midway between the extremes of color-light and color-strength,--and are known as MIDDLE RED, MIDDLE YELLOW, MIDDLE GREEN, MIDDLE BLUE, and MIDDLE PURPLE. These are starting-points for training the eye to measure regular scales of Value and Chroma.[23] Only with such a trained judgment is it safe to undertake the use of strong colors.[24] [Footnote 23: See Century Dictionary for definition of chroma. Under the word “color” will be found definitions of Primary, Complementary, Constants (chroma, luminosity, and hue), and the Young-Helmholtz theory of color-sensation.] [Footnote 24: It must not be assumed because so much stress is laid upon quiet and harmonious color that this system excludes the more powerful degrees. To do so would forfeit its claim to completeness. A Color Atlas in preparation displays all known degrees of pigment color arranged in measured scales of Hue, Value, and Chroma.] _Beginners should avoid Strong Color._ Extreme red, yellow, and blue are discordant. (They “shriek” and “swear.” Mark Twain calls Roxana’s gown “a volcanic eruption of infernal splendors.”) Yet there are some who claim that the child craves them, and must have them to produce a thrill. So also does he crave candies, matches, and the carving-knife. He covets the trumpet, fire-gong, and bass-drum for their “thrill”; but who would think them necessary to the musical training of the ear? Like the blazing bill-board and the circus wagon, they may be suffered out-of-doors; but such boisterous sounds and color sprees are unfit for the school-room.