each of them can be measured. Thus in
the case of the boy's faded cap its redness or HUE[3] is determined by
one instrument; the amount of light in the red, which is its VALUE,[3]
is found by another instrument; while still a third instrument
determines the purity or CHROMA[3] of the red.

The omission of any one of these three qualities leaves us in doubt as
to the character of a color, just as truly as the character of this
studio would remain undefined if the length were omitted and we
described it as 22 feet wide by 14 feet high. The imagination would be
free to ascribe any length it chose, from 25 to 100 feet. This length
might be differently conceived by every individual who tried to supply
the missing factor.

(9) To illustrate the tri-dimensional nature of colors. Suppose we peel
an orange and divide it in five parts, leaving the sections slightly
connected below (Fig. 4). Then let us say that all the reds we have ever
seen are gathered in one of the sections, all yellows in another, all
greens in the third, blues in the fourth, and purples in the fifth. Next
we will assort these HUES in each section so that the lightest are near
the top, and grade regularly to the darkest near the bottom. A white
wafer connects all the sections at the top, and a black wafer may be
added beneath. See Plate I.

[Illustration: Fig. 4.]

[Footnote 3: For definitions of Hue, Value, and Chroma, see
paragraphs 20-23.]

(10) The fruit is then filled with assorted colors, graded from white to
black, according to their VALUES, and disposed by their HUES in the five
sections. A slice near the top will uncover light values in all hues,
and a slice near the bottom will find dark values in the same hues.
A slice across the middle discloses a circuit of hues all of MIDDLE
VALUE; that is, midway between the extremes of white and black.

(11) Two color dimensions are thus shown in the orange, and it remains
to exhibit the third, which is called CHROMA, or strength of color. To
do this, we have only to take each section in turn, and, without
disturbing the values already assorted, shove the grayest in toward the
narrow edge, and grade outward to the purest on the surface. Each slice
across the fruit still shows the circuit of hues in one uniform value;
but the strong chromas are at the outside, while grayer and grayer
chromas make a gradation inward to neutral gray at the centre, where all
trace of color disappears. The thin edg