The next morning, when Mary came out in the garden to sit with Harry, she was surprised to see an audience of three instead of one: Harry, whose face beamed with delight when he saw her; Nellie, who was seated in a tiny rocking chair beside him, and Nellie's doll.

"You see, dollie wants to know all about Giant Sun, too," Nellie gravely informed Mary. "I never could remember all, and she might remember what I forget. Besides, she must learn some day. That is what mamma said about me. I heard her," Nellie continued wisely, as she looked up at Mary. "Do you mind telling me about the sky-people too?"

"Mind? Why you little bit of a doll baby," laughed Mary, as she picked her up, doll and all, and hugged her, "if you and dollie promise not to go to sleep, you can stay here as long as you want to. But does Aunt Agnes know you are here, Nellie; or have you run away from home?"

"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."

"But we don't know whether there are any people there," continued Mary, "and if there are, they might not mind the heat at all. You can get used to the heat, just as Uncle Robert did when he went to India. Don't you remember how he felt the change when he came home, and how he shivered? He missed the heat just as we would suffer from it if we went to India for the first time."

"Then Uncle Robert would not mind going to Mercury," said Harry, laughing, "if he is getting to like the heat in India. But I do not want him to go yet, as he might never come back again; and what would we do without him?"

"What would we?" said Nellie mournfully, her eyes filling with tears at the very thought.

"Is a planet made of earth and stones and trees and flowers, just like planet Earth?" asked Harry.

"Yes, dear," replied his sister; "only some planets, like Jupiter and Saturn, are still wrapped up in a blanket of clouds and steam, and we cannot see them yet. They are very hot indeed, and all the water that will make the oceans and seas and bays is now steam and clouds hiding the true planet from view. Water could no more rest on the surface of the planets Jupiter and Saturn than it could rest on red-hot iron. Don't you remember, the other day, when nurse upset a cup of water on the hot stove, how the water sizzled and turned into steam in a moment?

"Now planet earth, a long time ago, when it was a very young world, was very hot like Jupiter. All the lakes and seas and oceans were turned into steam and blankets of cloud. It would have been a very uncomfortable world to live on then. But it became cooler and cooler, and the clouds changed into the oceans and seas and lakes that make our earth so beautiful.

"Some day this little world will grow old, and the oceans will get smaller and smaller, and the earth colder and colder. Then there will be scarcely any air to breathe, and we would gasp, and die just like that poor fish that Uncle Robert caught last week and threw in the bottom of the boat. Don't you remember, Nellie, how the poor little thing gasped and jumped around? It could not live out of the water, so it died. Now, we cannot live without air, and if this earth had not any air we would die. But this will not happen for a very long time."

"Are you quite sure?" asked Harry, with an anxious look on his face; "because I don't want to die yet, sister."

"Quite sure, my little brother," she said, kissing him tenderly; "for hundreds and hundreds of years must pass away before anyone will have any idea that the earth is growing old."

"And what will become of the poor little fishes when the oceans dry up?" asked Nellie sadly, as she clasped her dollie closely in her arms, as though to protect it from the coming trouble.

"I expect they will all die," said Harry wisely; "because you know, Nellie, they can't live out of water. Can they?"

"Or else that fish Uncle Robert caught would have lived," said Nellie. "But please tell us a story about Mercury, Cousin Mary, and the other little planets."

"Well, Mercury is a very little planet, and instead of taking a year of three hundred and sixty-five days, it goes around the sun in eighty-eight days. That is, it goes round the sun four times while we go round it only once. Some think Mercury always keeps the same side turned to the sun, so that it is always day on one side and night on the other, but we are not quite sure about this yet."

"I should like to live on Mercury, wouldn't you, Harry?" said Nellie, clapping her hands with glee. "Just think of day all the time, and never having to go to sleep!"

"But you would get very tired of that," said Mary, "and long for the night to come. And, besides, would you not miss seeing the moon and the beautiful stars?"

"I would live on the edge of Mercury," said Harry thoughtfully, "so that when I was tired of day I might slip around it and have night. It must be very cold on the other side, where the sun does not shine, if Mercury gets all its heat from the sun."

"I suspect it is," said Mary, "and I don't believe we should like to live on Mercury, after all; so let us try the next planet, which is called Venus."

STORY OF PLANET VENUS.

"What a pretty name," said Nellie; "and is Venus very warm, like Mercury?"

"It is not so near to the sun," replied Mary, "but it is about twice as warm and bright as our planet. Venus is nearly as large as the earth, and sometimes she is called her twin sister.

"Like Mercury, she may probably always turn the same face to the sun, and get baked on one side and frozen on the other. She looks like a beautiful silver globe in the sky. Sometimes we see her early in the morning as a morning star, or just about twilight as an evening star. Like Mercury and the earth, she borrows all her light from the sun. We only see her because the sun is shining on her. Next to Venus is our own planet, earth, and around it circles the moon, but I must tell you about that another time."

ESTELLE'S ASTRONOMY.

BY DELIA HART STONE.

VENUS.

Fairest of stars, last in the train of night,

If better thou belong not to the dawn,

Sure pledge of day, that crown'st the smiling morn

With thy bright circlet.