duce white. Strictly, the colors--or
at least the color sensations--are not mixed; for when yellow and blue
lights are mixed, the resulting sensation is by no means a mixture of
blue and yellow sensations, but the sensation of white in which there
is no trace of either blue or yellow. Mixing the stimuli which, acting
separately, give two complementary colors, arouses the colorless
sensation of white.

Blue and yellow, then, are complementary. Suppose we set out to find
the complementary of red. Mixing red and yellow lights gives the
color-tones intermediate between these two; mixing red and green still
gives the intermediate color-tones, but the orange and yellow and
yellowish green so got lack saturation, being whitish or grayish. Now
mix red with bluish green, and this grayishness is accentuated, and if
just the right wave-length of bluish green is used, no trace of orange
or yellow or grass green is obtained, but white or gray. Red and
bluish green are thus complementary. The complement of orange light is
a greenish blue, and that of greenish yellow is violet. The typical
green (grass green) has no single wave-length complementary to it, but
it does give white when mixed with a compound of long and short waves,
which compound by itself gives the sensation of purple; so that we may
speak of green and purple as complementary.

What Are the Elementary Visual Sensations?

Returning now to the question of elementary sensations, which we laid
aside till we had examined the relationship of the sensations to the
stimulus, we need to be on our guard against physics, or at least
against being so much impressed with the physics of light as to forget
that we are concerned with the _response_ of the organism to physical
light--a matter on which physics cannot speak the final word.

{217}

Fig. 36.--(After Koenig.) The color triangle, a map of the laws of
color mixture. The spectral colors are arranged in order along the
heavy solid line, and the purples along the heavy dotted line. The
numbers give the wave-lengths of different parts of the spectrum.
Inside the heavy line are located the pale tints of each color,
merging from every side into white, which is located at the point W.

Suppose equal amounts of two spectral colors are mixed: to find from
the diagram the color of the mixture. Locate the two colors on the
heavy line, draw a straight line between these two points, and the
middle of this line