in cup that would just take in the box, and
turning into the cup as much water as he judged, with the box, would fill
it, he presented them separately to the boy, and said,

"There, my lad, tell me which of these is the heavier."

13. "Why, the cart box, to be sure," replied the boy, taking the cup,
half-filled with water, in one hand, and the hollow iron in the other.

"Then you think this iron is heavier than as much water as would fill the
place of it, do you?" resumed Locke.

"Why, yes, as heavy again, and more too--I know it is," promptly said the
boy.

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."

18. "Why, why, heavy things settle down, and the cold air--yes, yes,
that's it, I am sure--the cold air is heavier, and so settles down, and
crowds up the warm air."

"Very good. You then understand that cold air is heavier than the heated
air, as that iron is heavier than the water; so now we will go back to the
main question--what makes the smoke go upwards?"

19. "Oh! I see now as plain as day; the cold air settles down all round,
like the iron box, and drives up the hot air as fast as the fire heats it,
in the middle, like the water; and so the hot air carries the smoke along
up with it, just as feathers and thin