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One-half of the answer to this is: As bears sleep most of the time in a warm place in winter, they do not need as much food as when they are active. The other half is that they eat themselves. In the summer months they eat greedily, a great deal more than they need at the time. This extra food is stored up in their bodies in thick layers of fat. This fat keeps the sleeping bear warm. Food is fuel. As he is very warm in his blanket of fat, a bear needs less food. And, gradually, he eats the blanket. The fat is absorbed into the blood to feed all the other tissues of the body. In the spring the bear comes out thin and poor.

Many other animals hibernate in the winter. Snakes store up fat to live on. You see there is little food for them in winter, so Nature taught them how to stock up their internal pantry shelves for hard times. When you are sick and can not eat as much as usual, you, too, live partly on the fat stored in the body. That is why you become very thin. And that is why, when you begin to get well, you are as "hungry as a bear."

That is a hard question! But it isn't a foolish one, by any means. It was only about fifty years ago that a great English scientist named John Tyndall worked out the puzzle. See if you can understand the answer.

The sun is 92,897,000 miles away from us, but the sun's white rays come to us straight, with no interference, until they strike the earth’s atmosphere about forty miles above our heads. This atmosphere absorbs, or swallows up the light rays. If this were all the sun should look to us like a great star, and the sky at midday should appear dark and clear as on a winter night, with all the stars shining. Long ago scientists noticed that on very high snow-covered mountains, and out in mid-ocean where the air is purest, the sky is darker than it is over low land. The air near the earth, that is heavy enough to be breathed, is full of line earth-dust. These dust particles catch and break up the light rays, just as a glass prism, or a diamond breaks a ray of white light up into rainbow colors. Now if all those rays could get through to us we would have a rainbow sky. But the impurities are of just the right size and number to throw back all the other colored rays, and to reflect the blue rays to us.