them and absorbed, others rebound from them like a ball from a wall; and
these last, breaking upon the optic nerve, give to it certain sensations
which we designate as colors. A wave of a certain velocity and length
gives us a certain sensation which we call blue; another awakens the
sensation we call yellow. The two series of waves, mingling, produce a
new sensation which we call green. The necessity of reflection for the
production of these sensations is evident. The mingled waves have no
color in their incident flow; but, striking some object, these waves
become separated, some being absorbed, and the reflected ones produce
the peculiar sensation we call color.

We know that these varying conditions of light which affect us as color
have an absolute being. The photographer carries on his nice operations
behind a yellow screen undisturbed, when the substitution of a pink one
would at once allow of the chemical action of the other rays of light on
his plate, to the destruction of his image. Still, the pink and the
yellow, as colors, are brain sensations. We feel them with our eyes, and
the feeling they awaken we call color. The optic nerve receives the
undulations of ether thrown back from grass, and the peculiar sensation
thus awakened by their touch is called green. The color is not a part of
the grass, not a quantitative constituent, like its carbon or silex. The
grass has no color, because color is something existent in the eye of
the beholder, not in the object awakening that something by its peculiar
mode of reflecting light. A looking-glass does not possess, as a
constituent part, the image of a human face; but that face, when put
before it, appears to be a part of the glass; and if no looking-glass
had ever existed except with a certain face before it, that face would
be just as much a part of the glass as the color green is of grass. They
both reflect. Some people are color-blind. They cannot perceive any
difference between the rose and the leaves around it. Color is
inconceivable to them. Let us suppose, then, that all men were
color-blind. They would be fully cognizant of light, shadow, darkness;
but the nicer sensations of the brain which we call colors would be
utterly unknown to senses unable to feel their delicate touch. At the
same time, the different undulations of the different colors might have
been detected by other means than the sense of sight, as unseen gases
have been discovered by the chemist. A