he put it on the wheel, but it was still loose. We couldn't have gone a
step without its coming off again. He brought cold water and poured over
it, and soon it was as tight as could be. I thought the water made the
wood of the wheel swell up--you know water does that to the pails and
tubs when they leak; but now I believe the fire made the tire larger, and
then the cold water made it small again. That is just what happened."

[Illustration: The blacksmith shop.]

"But air can't grow bigger, can it?" asked Donald.

"If you can find an empty bottle, Donald," said Uncle Robert, "perhaps
we can soon find out about it."

Uncle Robert took a piece of thin rubber out of his pocket and tied it
tightly over the mouth of the bottle."

"By the way," he said, "is there anything in this bottle?

"No," said Susie, looking through the glass.

"Oh, yes," said Donald, "there is air in it."

"Well," replied Uncle Robert, "please get a pan of hot water, Frank."

Frank brought the water, and as Uncle Robert began to put the bottle
into it they all exclaimed:

"Be careful; you'll break the bottle!"