"Oh, yes," said the three children together.

"I saw a star fall, so fast--just like a rocket. Then the light went out, and I wondered where it went," said Susie.

"Falling stars are not stars at all, though they look like them. They are pieces of rock that break off from other worlds and whiz through s.p.a.ce."

"Oh!" said Susie.

"Outside of our atmosphere there may be nothing for these ma.s.ses of rock to strike against, but just as soon as they come into the air, it tries to stop them. The air is not strong enough to stop them, but it grinds them up."

"Grinds them up!" exclaimed Donald. "Isn't that wonderful? But, uncle, what makes them look just like fire?"

"If you put an axe or scythe on a dry grindstone and turn the crank, what do you see?"

"Sparks of fire," said Frank.

"Why do you put grease or oil upon the axles of your buggy?"

"To keep them from becoming hot and dry," said Frank. "One time when father and I were on a train there was a hot box, and we had to stop to cool it."

"The heat and the sparks of fire are caused by one body rubbing against another. The faster they move, the greater the heat. This rubbing is called friction."

"There was a time," said Mr. Leonard, "when fires were started by rubbing two pieces of wood together. Some Indians do so now."

"Then the great pieces of rock rub against the air when they whiz through it, and that makes the sparks?" asked Frank.

"You are right. We can see the blaze of fire caused by the friction."

"I should think the rocks would fall on us and kill us," said Donald.

"Most of them are probably ground up into bits of dust before they reach the ground. Some of them, indeed, do strike the ground, and very large ones bury themselves deep in the earth. When we go to the Field Columbian Museum, in Chicago, we shall see these visitors from other worlds. They are called meteoric stones, or meteorites. When they are in the air we call them meteors."

"I am going to watch the next one I see," said Susie.

"They fly so fast that you hardly see them before they are gone," said Donald.

"Men who study the heavens tell of the depth of the atmosphere by the angle the meteor makes in falling, but perhaps you can not understand that now. So you see, children, we live on the bottom of a great ocean of air, and that air, or atmosphere, is a part of our world--the outside part."

"How plain it all is," said Mrs. Leonard, "when we think of it this way!"

"Now we have the land and the water," said Uncle Robert.

"And the atmosphere," put in Donald.

"And they are all right here close to us. Here is the land with its hollows, and there," pointing to the river glistening in the moonlight, "is the water, and--"

"You can't see the air," said Donald.

"We can feel it, anyway," said Susie.

"How large is the earth, uncle?" asked Frank.

"Eight thousand miles through it and twenty-five thousand miles around it," answered Uncle Robert.

"But, uncle, is it all solid rock for eight thousand miles?"

"No one knows. The rocky outside of the ball is called the crust of the earth. Miners have dug down nearly four thousand feet, and makers of artesian wells have bored still farther. They always find rock."

"I wonder how far four thousand feet would be," said Donald.

"A little over three quarters of a mile," said Mr. Leonard.

"The farther they go down into the crust of the earth, the warmer they find it. I have been down in a mine thirty-two hundred feet, and it was very hot. No one could have lived there if cool air had not been brought down from the surface.

"Some people have thought that inside the crust of the earth the rock is all a molten ma.s.s, like melted iron. You have read about volcanoes, and of the lava that is thrown out of them?"

"Does that come out of the inside of the earth?" asked Donald.

[Ill.u.s.tration: Down in a Gold Mine]

"It comes from somewhere in the earth. Some men give their whole lives to the study of these questions, but you know they can not see beneath the crust of the earth. It is thought by some that the weight of the crust would keep the center of the earth a solid ma.s.s. So you see there are still many questions unsettled. We know that the crust is moving up and down all the time."

"Oh, I hope the land won't rise here!" said Susie.

"You wouldn't know it, Susie, if it did," said Uncle Robert, laughing.

"Unless there was an earthquake," said Frank.

"Or a volcano," said Donald. "I'd like to see one."

"I would like to see the ocean," said Frank. "It must be grand to stand on the sh.o.r.e and look way off and not see anything but water."

"It is a grand sight, Frank. I have sat on the beach many a time and watched the waves roll in, and thought of the wonderful work the ocean is doing. You know it is the great reservoir that supplies all the land with water."

[Ill.u.s.tration: View of the Ocean]

"The heat of the sun lifts the water up, or evaporates it. The vapor that makes the clouds rises into the air. The winds blow the vapor many long miles, and some of the clouds come right over our heads. The cold air draws the little bits of vapor together and makes the clouds heavy, and down they fall upon the earth as drops of rain.

"Some of the rain runs directly into the streams. Some of the rain water sinks down into the earth; in the gravel it sinks fast; in the sand it sinks slower; and in the loam, clay, and rock it sinks very slowly indeed. The water in the ground dissolves the rock or the loose earth into little particles so fine that the tiny roots, or root hairs, drink them up, and so the rock furnishes a part of the nourishment, or food, of plants.

"Without the water that the clouds bring no plant could grow. It gives life and growth to everything that lives, and then sinks deep into the earth. It comes out of the ground again in springs, and flows away in rivulets, brooks, creeks, and rivers--away, and away, back to the ocean again.

"On its way to the ocean it wears down the land, carries silt from place to place, spreads it out on beaches, sand bars, bottom lands, deltas, and on the bottom of shallow places in the ocean."

"Isn't it strange how everything changes, and how all the changes help us?" said Frank thoughtfully.

"Yes, Frank, it is wonderful how the Creator of all things is constantly moving earth, air, and water, and, as you say, making all these changes to help man."

"It is the Big Book that tells us of this marvelous world of ours and of other worlds as well. It lies open before us for us to read every day.