[Illustration: GIANT SUN AND HIS FAMILY.] "No, I have not run away," said Nellie earnestly, "but my dollie has. Nurse brought me over here, but she did not know my dollie was here. I forgot all about her yesterday, while Harry was telling me about Giant Sun, and I left her out on the grass. But she didn't melt a bit. I knew you wouldn't, dear little dollie, would you? Now, dollie, sit up straight, and listen to Cousin Mary talk. My, how she can talk, too! Can't you?" "I'll try," said Mary, laughing. "So you want to hear about Giant Sun and his family. He has such a large family, and he has to give them all plenty of light and heat. If he put out his big lamp in the sky, it would be always dark here, and we would shiver with cold and die. When I come to your room at night, Harry, to say good-night, I always carry a lamp in my hand so that I can see you; but supposing a puff of wind blew it out, then I could not see you at all. "Now this light is not only for us, but for the rest of the sun's family as well. First, there is little Mercury, who was named after the god of thieves; and he deserves this name, because he steals more light and heat from the sun than any of the other planets." WHAT IS A PLANET? "What is a planet?" asked Harry. "A planet is just like this earth we are living on, and only shines with the light it borrows from the sun. If we lived on planet Mercury, and could look at our earth, we would see it shining like a bright star in the sky; but all the light comes from the sun." "Do we live on a star, then?" asked Nellie, her little eyes wide open with amazement. "No; we live on a planet. We could not live on a star, as a star is blazing hot. That is the difference between a star and a planet. A star is hot and bright and shining and gives light to the planets, if it has any. Planets are little globes like the earth that circle around the sun." "Then the sun must be a star," said Harry, "as you told me yesterday that it is very hot." "That is right," said Mary; "and every star in the sky is a sun." "And has lots of weensy-teensy planets going all around it?" asked Nellie excitedly. STORY OF PLANET MERCURY. "Some of them have, I am sure," said Mary. "But now we are running along too fast, and I must tell you about our own sun first, and its nearest planet Mercury. Well, Mercury is a very warm little world, and it gets so near the sun that sometimes it is about nine times as warm as here, and at other times it is only four times as warm. You see, Mercury does not go round the sun in a perfect circle, so at times it is farther away than at others. Now, the sun is like a great fire in the sky, and the nearer we go to it the warmer we are. How would you like to live on a little world where it is nine times warmer than it is here?" "I should not like it at all, would you, dollie?" said Nellie; "we would roast if we went to world Mercury."