nd we cannot say that Nature may
not possess an inconceivable variety of influences inappreciable by our
senses. We say grass is green; but is it always so? What varying colors
does it possess under the varying light to which it is exposed. The same
grass is light green in the sun, dark green in the shadow, almost black
in the twilight, and at night what color is it? We may say that it is
green, but that we cannot see it. By no means. If greenness were an
inherent attribute, it would be persistent. The weight, density,
chemical construction, and size of the plant do not change from midday
to midnight. They are identical in the dark and the light. But the color
depends entirely on the character of light poured upon it; as that color
is only a peculiar reflection of that light, or part of it, and that
reflection is only green when it stimulates an optic nerve to a
sensation peculiar to its touch. The same grass becomes yellow or brown
in autumn, possessing then new powers of absorption and reflection. The
very limited capacity of the eye to receive sensation from light rays is
proved by the discovery that the spectrum possesses other rays, called
heat-rays, which the eye cannot perceive. Only about a third of the
spectrum is visible to the eye. The other portion appears in the form of
heat, inappreciable by the optic nerve as light.

Color, therefore, is not a physical thing,--a quantity in Nature. Her
beauty and glory, visible in her tints and hues, are in the brain of the
observer,--a play of light reflected from the myriad objects upon which
it breaks in infinite diversity of ethereal wavelet's. One may see
colors which do not exist as undulations. For example, let one look
fixedly at a brilliant red object for a while, and then close his eyes.
He will behold an image of the same object of a green color. This green
color, then, is a sensation in the optic nerve, which, being powerfully
stimulated by the red, undergoes a reaction, resulting in a sensation
similar to that which it would experience were it looking at the object
in green. The color green, in this case, is certainly only nervous
sensation. As light is now known to be the motion of matter, color, as
the result of light, must inevitably be limited by it. The touch of the
light-waves upon our nerves causes certain contractions which we call
color, the contractions ceasing when the touch is withdrawn. A pane of
green glass will cast upon a white marble a green l