COMPARATIVE SIZE OF SUN AS SEEN FROM THE PLANETS.
"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.
COMPARATIVE SIZE OF THE PLANETS.
"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."