14. "Well, sir, now mark what I do," proceeded the former, dropping into the cup the iron box, through the hollow of which the water instantly rose to the brim of the vessel.
"There, you saw that water rise to the top of the cup, did you?"
"Yes, I did."
"Very well, what caused it to do so?"
15. "Why, I know well enough, if I could only think: why, it is because the iron is the heavier, and as it comes all around the water so it can't get away sideways, it is forced up."
"That is right; and now I want you to tell what makes that smoke rise up the chimney."
16. "Why,—I guess," replied the boy, hesitating, "I guess,—I guess I don't know."
"Did you ever get up in a chair to look on some high shelf, so that your head was brought near the ceiling of a heated room, in winter? and did you notice any difference between the air up there and the air near the floor?"
17. "Yes, I remember I have, and found the air up there as warm as mustard; and when I got down, and bent my head near the floor to pick up something, I found it as cold as could be."
"That is ever the case; but I wish you to tell me how the cold air always happens to settle down to the lower part of the room, while the warm air, somehow, at the same time, gets above."