Page:Popular Science Monthly Volume 4.djvu/433

Rh gradually into an orange tint, and, gaining greatly in luminosity, becomes pure yellow; passing thence by gradations into green and blue, it gently fades out in a violet and faint violet-gray or lavender. Beyond this point are yet more minute waves, but, in pursuing them, we enter once more what is for us a region of silence and darkness, and we are compelled to feel our way with the help of photographic plates.

The series of tints just mentioned is now on the screen, and, were it worth while, the existence of systems of invisible waves upon either side could easily be demonstrated. The statements that I have made lead us, however, a little unexpectedly to a remarkable conclusion. They show that the beautiful colors now displayed have no existence outside of ourselves—that, outside of ourselves, there are merely waves, longer or shorter. Color is a sensation existing merely in ourselves. On the other hand, our eyes might have been made quite insensible to color while still preserving the power of vision, and it is not impossible for us to conceive the existence of beings to whom the luminous waves might only be what to us are the breakers on a sea-beach.

But, to resume: if we allow all these luminous waves to act simultaneously upon the eye, we obtain, not, as might perhaps be expected, a still richer and more gorgeous tint, but simply the sensation called white—brightness without color.

Now, it happens somewhat remarkably that all the color sensations I have mentioned, and all intermediate ones, can be approximately reproduced by the mixture in various proportions of merely three powders: when viewed by ordinary daylight one of the powders must be capable of reflecting red light, the others yellow and blue light respectively, that is to say, they must reflect abundantly the waves capable of producing these three sensations; the rest of the waves falling on them they must absorb and destroy, to a greater or less extent; or, finally, in common language, out of the mixture of red, yellow, and blue pigments, all the colors can be produced. This fact has been known for ages—it was old in the time of the Greeks, and probably dates back to that early period when the first serious attempts at painting were made by the human race. What could be more natural than that it should lead to the theory of the existence of only three primary colors, red, yellow, and blue, out of which all the others could be compounded: thus, orange out of a mixture of red and yellow, green by blue and yellow, and violet from red and blue. This theory was firmly established before Newton's time. During the present century it was the glory of one of England's greatest physicists that he had strengthened its foundations (it is found in most text-books on physics and art), and is to-day almost universally credited by painters. We have here upon the screen its well-known typical expression: three overlapping circles, the red one producing orange where it crosses