Using the left hand again to hold colors, the principal hues remain unchanged on the knuckles, but in the hollows between them are placed intermediate hues, so that the circle now reads: red, yellow-red, yellow, green-yellow, green, blue-green, blue, purple-blue, purple, and red-purple, back to the red with which we started. This circuit is easily _memorized_, so that the child may begin with any color point, and repeat the series clock wise (that is, from left to right) or in reverse order. [Footnote 17: Orange is a variable union of yellow and red. See Appendix.] (59) Each principal hue has thus made two close neighbors by mixing with the nearest principal hue on either hand. The neighbors of red are a yellow-red on one side and a purple-red on the other. The neighbors of green are a green-yellow on one hand and a blue-green on the other. It is evident that a still closer neighbor could be made by again mixing each consecutive pair in this circle of ten hues; and, if the process were continued long enough, the color steps would become so fine that the eye could see only a circuit of hues melting imperceptibly one into another. (60) But it is better for the child to gain a fixed idea of red, yellow, green, blue, and purple, with their intermediates, before attempting to mix pigments, and these ten steps are sufficient for primary education. (61) Next comes the question of opposites in this circle. A line drawn from red, through the centre, finds its opposite, blue-green.[18] If these colors are mixed, they unite to form gray. Indeed, the centre of the circle stands for a middle gray, not only because it is the centre of the neutral axis between black and white, but also because any pair of opposites will unite to form gray. [Footnote 18: Green is often wrongly assigned as the opposite of red. See Appendix, on False Color Balance.] (62) This is a table of five mixtures which make neutral gray: { Red & Blue-green } { Yellow Purple-blue } Opposites { Green Red-purple } Each pair of which unites { Blue Yellow-red } in neutral gray. { Purple Green-yellow } (63) But if, instead of mixing these opposite hues, we place them side by side, the eye is so stimulated by their difference that each seems to gain in strength; _i.e._, each _enhances_ the other when separate, but _destroys_ the other when mixed. This is a very interesting point to be more fully illustrated by the help of a color wheel in Chapter V., paragraph 106. What we need to remember is that the mixture of neighborly hues makes them less stimulating to the eye, because they resemble each other, while a mixture of opposite hues extinguishes both in a neutral gray. +Hues once removed, and their mixture.+ [Illustration: Fig. 8.]