I have told you that light is sometimes reflected more than twice, even many times. When you look at a person in a room into which the sun is not directly shining, where does the light by which you see him come from? It is not the light that comes straight from the sun, for this is not shining upon him. It is the light reflected from things around him. This reflected light strikes upon him, and is thus again reflected from him, and some of it enters your eyes, enabling you to see him.
Light reflected back and forth.
Light is thus reflected back and forth from one thing to another; and a great deal of light is reflected from every thing all the time, and in all directions. Suppose a great assembly are all looking at one person. The light is reflected from him, and goes into a thousand eyes at once in all parts of the house, making a picture of him in all of them. What a wonderful painter light is! How many pictures it is making all the time in the eyes of men and animals, and on mirrors and all smooth things every where!
Light makes plants and animals grow.
Another use of light is to make plants and animals grow. I have told you in Part I. how plants turn toward the light, as if they loved it. It really has a great deal to do with their growth.
This is very plain whenever we see a plant that has grown in the dark. It looks pale and sickly. A good deal of light is needed as really as a free circulation of air to make plants healthy and strong; and the same is true of animals. People that live in dark, under-ground rooms in cities are injured by the want of light as well as by the want of good air.
Most of the light in the world comes from the sun. It comes from there with the heat, as I have before told you. They travel in company. It is a very long journey. It is many millions of miles. The light is a little more than eight minutes coming from the sun to the earth.
Light travels faster than sound.
Light travels very fast. It travels faster than sound does. You see a man cutting wood a considerable distance off, and you hear the sound of each blow of his axe a little after you see it. The reason is that the light comes from him to your eye quicker than the sound comes to your ear. You see a cannon fired at a distance; you first see the flash, and then afterward hear the report. The thunder comes generally some time after the flash that causes it; that is, the light of the flash gets to your eye some time before the sound of it reaches your ear. By observing, it has been found out just how fast sound and light travel; and so, by looking at a watch in a thunder-storm, we can tell how far off the lightning is.