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. And 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 wavelets. 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 lightwaves 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 light. Let us suppose that this play of light had always existed, so far as those two objects were concerned. The marble would appear to be permanently green, and not white; and if we had not a simple way of removing the light, we should certainly say it was green marble. Could we as effectually change the play of light which causes grass to appear green, we should at once demonstrate as readily, that its color was an appearance to the eye, not a part of the grass itself. It is very probable that we are extensively deceived in this way,—that many appearances in nature are only simulations which we have no means of detecting. Isomerism in minerals has been discovered, a state in which quite different physical properties are coexistent with identity of component parts. What we always see, and
