the most knowledge to appreciate.

=Scientific Color.=--To the scientist color is simply the irritation
of the nerves of the retina of the eye by the waves of light.
Different wave lengths give different color sensations. It is the
generally accepted theory now that there are three primary sensations;
that is, that the eye is sensitive to three kinds of color, and that
all other shades and varieties of color are the results of mingling or
overlapping of the waves which produce those three colors, and
irritating more or less the nerves sensitive to each color
simultaneously. These three primary colors are now stated to be red,
blue, and _green_. The older idea was that they were red, blue, and
_yellow_; and was based on experiments with pigments. Pigments do give
these results; for a mixture of blue and yellow _pigment_ will give
green, and a mixture of red and green _pigment_ will not give yellow,
while the reverse is the fact with _light_.

White light is composed of all the colors. And the white light may be
broken up (separated by refraction or the turning aside of light rays
from their true course) into the colors of the rainbow, which is
itself only this same decomposition of light by atmospheric
refraction. Black is the absence of light, and consequently of color.
This is not the case with pigment, for pure pigment has never been
produced. The pigment simply reflects light rays which fall on it;
that is, pigments have the power of absorbing, and so rendering
invisible, certain of the rays which, combined, make up the white
light which illumines them; and of transmitting others to the eye by
reflection. We see, that is, our nerves of sight are irritated by,
those rays which are not absorbed, but which are reflected.

All pigment is more or less absorbent of color rays, and more or less
reflective of them; certain color rays being absorbed by a pigment,
and certain other rays being reflected by it. The pigment is named
according to those rays which it reflects. As a color-producing
substance, then, the pigment is practically a mirror reflecting color
rays. But a true mirror would reflect all rays unmodified. If we could
paint with mirrors, each of which would reflect its own color
_unsullied_, we could do what the scientist does with light; but the
painter deals with an imperfect mirror which gives no color rays back
unsullied by rays of another class, and so our results cannot be the
same as the scientist's. So