CHAPTER XXVII.
COLOR.
Why the sun’s light is white.
Made up of seven colors, as Newton showed.
The light that comes from the sun is, you know, a white light. Now in this white light are the different colors of the rainbow. Indeed, it is these colors mixed together that make the white color of the sun’s light. This was proved by Sir Isaac Newton in this way: He had a hole in a shutter through which he let a very little of the sun’s light into a dark room. He had a screen for it to strike upon, and on this it made a bright white spot. He then let it shine through a three-cornered piece of glass, called a prism. This turned the ray of light out of its way, and made it shine upon another part of the screen; and, besides this, the spot of light on the screen, instead of being round, as it was before, was now lengthened out, and had seven different colors in it.
All this is represented on this figure. At O is the hole in the shutter, and m is a mirror by which a little of the bright sunlight is thrown into this hole. Without the prism it would go straight to the screen, S r, and make a round white spot where the word white is. But with the prism, P, the beam of light is turned out of its straight path, and is divided into the different colors as marked in the figure. The reason that these colors are seen so distinct from each other is, that they are bent out of their way in different degrees—the orange a little more than the red, the yellow a little more than the orange, and so on, the violet being most bent of all. You see this represented on the figure.
Colors in ice.
This and various other experiments, tried by Newton and others, show that the white light of the sun is not a simple thing. It can be cut up, as we may say, into different parts. The glass prism does this. You have often seen it done without thinking much about it. You have seen it done by ice. When there has been a rain, and the rain, as it fell, froze upon the branches of the trees, and the wind and the sun have together broken the ice on the trees, and strewed the ground with it, you have seen these pieces of the ice brilliant with all the colors into which they have divided the bright light of the sun. It seemed as if the ground was covered with gems of every hue; and as you looked up into the tree, it seemed to you that every twig also was strung with gems.
The rainbow.