oved, thus producing a color solid no larger than the chroma of its
weakest pigment (Fig. 2).

+Charts of the color solid.+

(125) Thus it becomes evident that, while the color sphere is a valuable
help to the child in conceiving color relations, in uniting the three
scales of color measure, and in furnishing with its mount an excellent
test of the theory of color balance, yet it is always restricted to the
chroma of its weakest color, the surplus chromas of all other colors
being thought of as enormous mountains built out at various levels to
reach the maxima of our pigments.

(126) The complete color solid is, therefore, of irregular shape, with
mountains and valleys, corresponding to the inequalities of pigments. To
display these inequalities to the eye, we must prepare cross sections or
charts of the solid, some horizontal, some vertical, and others oblique.

(127) Such a set of charts forms an atlas of the color solid, enabling
one to see any color in its relation to all other colors, and name it by
its degree of hue, value, and chroma. Fig. 20 is a horizontal chart of
all colors which present middle value (5), and describes by an uneven
contour the chroma of every hue at this level. The dotted fifth circle
is the equator of the color sphere, whose principal hues, R 5/5. Y 5/5,
G 5/5, B 5/5, and P 5/5, form the chromatic tuning fork, paragraph 117.

[Illustration: Fig. 20.

Chart of
Middle Value
- 5 -
Showing Unequal Chroma
in circle of Hues. (See Fig. 2).]

(128) In this single chart the eye readily distinguishes some three
hundred different colors, each of which may be written by its hue,
value, and chroma. And even the slightest variation of one of them can
be defined. Thus, if the principal red were to fade slightly, so that it
was a trifle lighter and a trifle weaker than the enamel, it would be
written R{5.1/4.9}, showing it had lightened by 1 per cent. and weakened
by 1 per cent. The discrimination made possible by this decimal notation
is much finer than our present visual limit. Its use will stimulate
finer perception of color.

(129) Such a very elementary sketch of the Color Solid and Color Atlas,
which is all that can be given in the confines of this small book, will
be elsewhere presented on a larger and more complete scale. It should be
contrasted with the ideal form composed of prismatic colors, suggested
in the last chapter, paragraphs 98, 99, which was shown to be
impracti