3. "Oh, yes, if I could be sure of coming down

again."

4.

"You would be quite sure of that."

6. "You would, most likely, come down alive. Even if you were to fall from a great height, the fall might not hurt you."

it."

7. "No; but the earth would, when I reached

8. "Yes; you would hit it very hard, and it would hit you again with just the same force. The earth would not feel the blow, but you would. Action and reaction, you remember, are equal."

9. "It seems rather hard that the earth should attract any one who falls, and then hit him so tremendously for falling."

10. "You would find it hard, at all events, if you were to fall from a balloon. You will generally find that those who draw you into mischief will be the last to have any mercy upon you when you yield. The earth, however, is very good to us all as long as we are contented with our proper place upon it." 11. "What makes a balloon go up?'

II.

12. "The same force which would make you come down."

13. 'You don't mean the attraction of the earth?"

14. "I do."

15. "How can that be? The earth pulls all other bodies towards itself."

16. "Yes; but some are heavier than others. In pulling the heavier bodies down, it may squeeze the lighter ones up. Drop a large stone into a bucket full of water what happens?"

17.

"It makes a splash."

18. "Anything else?"

19. Yes; the stone sinks to the bottom, and the water rises and pours over the edge of the bucket."

20. What makes the water rise?"

21.

"The sinking of the stone."

22. "Yes; and that was caused by gravitation. Two bodies cannot occupy the same space at the same time. The stone turned the water out to make room for itself, and, by sinking through it, compelled it to rise. Now if you were to place a cork, or a block of wood, at the bottom of the bucket, where the stone is, what would happen?"

23. "The cork would rise through the water, and the water would sink and take its place."

24. "Yes; in this case the water would be the heavier, and it would send the cork up. Now I will show you a real air balloon. I'll put one end of this tube at the bottom of the bucket, and then blow through the other. What do you see?"

25. "Bubbles rising."

26. "Bubbles! Air balloons, I call them. What makes them rise?"

27. "The air is lighter than the water.”

28. "Let us say, rather, the water is heavier than the air. Both are attracted by the earth; but the water, being attracted with greater force, slips under the air bubbles, and compels them to get out of its way as best they can. The air, therefore, goes to the top, which is its proper place; and when it meets with any other object lighter than itself, such as a balloon, it serves that in the same way, and sends it up."

29. "The air, then, is attracted to the earth, like anything else?"

30. "Certainly it is. Now you understand why the balloon rises."

31. "Yes; it is lighter than the air, and the air, being attracted downwards, presses under it, and forces it up."

32. "Very good; but what makes the balloon so much lighter than the air?”

33. "The gas that is in the bag, I suppose."

34. "Good again. The balloon is filled with hydrogen gas, which is about seven times lighter, bulk for bulk, than atmospheric air. Therefore, when a large quantity of it is shut up in a bag, the