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 Polished metals and woods, painted surfaces, even glossy leaves reflect. The moon is quite dead and cold. It has no light of its own, but shines by the reflected light of the sun. Even a layer of air may become a mirror. This is the way in which it does so over the desert. As a rule, the air nearest the surface of the earth is heaviest, and light rays from the earth pass upwards through gradually lightening air without being stopped. Over hot, sandy deserts the layer of air on the earth becomes more heated and therefore lighter than air that is some distance above. Light rays are stopped by this denser air layer and reflected back. And just as a tree growing on the bank of a pond is reflected upside down in the water, so a reflection, or mirage, is often inverted in the sky. But sometimes it seems to be lifted and merely reversed as your face is in a mirror. Mirages occur over dry plains and also over the far northern oceans. One case is on record in which the entire north coast of France was reflected to a sea-coast town in England, a distance of fifty miles across the English channel. So you may readily believe that the mirage in the desert is the reflection of an oasis that may be a day’s journey distant.

Why we have both day and night following each other regularly once every twenty-four hours, is supposed to be very hard to understand. It isn’t explained to children in school until they get their big geographies in the sixth grade. But it's just as easy as anything.

You see the sun rise and set every day. In the evening the sun goes down the western sky—or seems to go down—until it is out of sight. Then it is dark. In the morning the sun seems to rise in the east, and we have day. The sun has motions of its own, but in relation to our earth it stands still. It is the earth that turns away from the sun in the evening, and toward it in the morning. Push a long hatpin through an orange. Now hold the orange by both ends of the pin, and level with the flame of a lamp. Let's play the lamp is the sun, and the orange the earth. You know, of course, that the earth is a very big, nearly round ball. It is about eight thousand miles through the middle and over twenty-five thousand miles around. The lamp stands still, and keeps right on shining. But its light can shine only on the side of the orange-earth that happens to be turned toward it. It couldn't reach around and shine