"Ever so much larger," replied Mary. "It is so large that if it were cut up into a million parts, each part would be larger than the earth. If we could weigh the sun in a pair of giant scales, it would take over three hundred thousand globes as heavy as the earth to make the scales even. If the sun were hollowed out, and the earth placed in the center, there would be room for the moon as well. Now the moon is thousands of miles from the earth, and yet the edge of the sun would be thousands of miles from the moon, as you will see in the picture. If a tunnel could be made through the center of the sun, and a train started going at the rate of a mile a minute, it would take six hundred days for the train to reach the other side of the tunnel. If this same train went around the edge of the sun it would take five years. A train going around the earth would take seventeen days to complete the journey." "But suppose we went around the sun in a big steamer, like the one Uncle Robert came over in; how long would that take?" asked Harry curiously. "Only fifteen years," said his sister, laughing. "If you had started when you were a little baby you would still have five more years to travel before you would get back again to the starting-point." "Then the sun must be very large," said Harry thoughtfully. "Let us call it GIANT SUN. Has it always been as large as it is now?" THE SUN IN THE DAYS OF ITS YOUTH. "Ever so much larger," replied Mary. [Illustration: THE SUN AND PLANETS FORMING OUT OF STAR-MIST.] "Once upon a time it was a ball of glowing gas reaching as far as the path of the last planet. The ball whirled around rapidly and the outer edge cooled. A ring formed and separated from the ball and whirled around on its own account, until it broke up into fragments. One of the fragments drew all the others toward it, and another ball was formed, but quite a small ball this time, called a planet. Just like the central ball, the planet kept whirling around, threw off a ring, the ring broke up into little pieces, and the pieces, coming together, made a little moon. The planet is Neptune, and it still has only one moon. Meanwhile the ball in the center kept whirling around, other rings formed other planets with their attendant moons, completing the family of Giant Sun. "The Sun is in the center and his planets circle around him. Next to him is playful little Mercury, then beautiful Venus, then our own planet Earth. Beyond it, we find ruddy Mars, the four hundred and fifty baby planets, giant planet Jupiter, the ringed planet Saturn, and the last two planets, Uranus and Neptune. All these planets are under the control of the sun, and cannot get away from him." "What is the sun made of?" asked Harry.