ity as
complements by uniting in equal areas to form a neutral mixture. It only
remains to apply them in their proper position on the sphere.

(112) A band is traced around the equator, divided in ten equal spaces,
and lettered R, YR, Y, GY, G, BG, B, PB, P, and RP (see Fig. 18). This
balanced red and blue-green are applied with the brush to spaces marked
R and BG, care being taken to fill, but not to overstep the bounds, and
the color laid absolutely flat, that no unevenness of value or chroma
may disturb the balance.

(113) The next pair, represented by Raw Sienna and Ultramarine, is
similarly brought to middle value, balanced by equal areas on the
Maxwell discs, and, when correct in each quality, is painted in the
spaces Y and PB. Emerald Green and Purple Madder, which form the next
pigment pair, are similarly tempered, proved, and applied, followed by
the two remaining pairs, until the equator of the globe presents its ten
equal steps of middle hues.

+An equator of ten balanced hues.+

(114) Now comes the total test of this circuit of balanced hues by
rotation of the sphere. As it gains speed, the colors flash less and
less, and finally melt into a middle gray of perfect neutrality. Had it
failed to produce this gray and shown a tinge of any hue still
persisting, we should say that the persistent hue was in excess, or,
conversely, that its opposite hue was deficient in chroma, and failed to
preserve its share in the balance.

[Illustration: Fig. 18.]

(115) For instance, had rotation discovered the persistence of reddish
gray, it would have proved the red too strong, or its opposite,
blue-green, too weak, and we should have been forced to retrace our
steps, applying a correction until neutrality was established by the
rotation test.

(116) This is the practical demonstration of the assertion (Chapter I.,
paragraph 8) that a _color has three dimensions which can be measured_.
Each of these ten middle hues has proved its right to a definite place
on the color globe by its measurements of value and chroma. Being of
equal chroma, all are equidistant from the neutral centre, and, being
equal in value, all are equally removed from the poles. If the warm hues
(red and yellow) or the cool hues (blue and green) were in excess, the
rotation test of the sphere would fail to produce grayness, and so
detect its lack of balance.[29]

[Footnote 29: Such a test would have exposed the excess of warm
color in