Uncle Roberts Geography | Page 9

Frank, looking at the little gray cylinder
when they brought it down. "It is six degrees higher than it was on the
floor."
"Why?" asked Uncle Robert.
"The heat must go up there," said Donald.
"It goes into the next room when the door is open," said Frank.
"Does it go outdoors?" asked Uncle Robert.
"Let's open the window and see," said Susie.
Frank opened the window, but, instead of feeling the warm air going
out, he felt the cool air coming in.
"Uncle," asked Donald, "isn't the room full of air already?"
"Yes," answered Uncle Robert.

"Then I don't see how any more can come in at the window."
"Are you sure none goes out?"
"I could feel it coming in," said Frank.
"Jane," asked Uncle Robert, "have you a candle?"
"Here is one, sir," said Jane, taking a candlestick from beside the clock
on the shelf.
Uncle Robert lighted it and held it near the window, just below the sill.
The flame flickered as the air from the window struck it, and then
turned straight into the room. He raised it just above the opening.
Instantly the flame pointed toward the window, but it did not flicker as
it had when held below the sill.
"The air must be going out up there," said Frank, "but it doesn't blow so
strongly as the air coming in."
"The air that comes in is cooler than the air that goes out," said Donald.
"What makes the water boil?" asked Uncle Robert, turning to the kettle
on the stove, which had now begun to sing.
"Why, the heat, of course," said Donald.
"What raises the lid?" asked Uncle Robert.
"The kettle is too full," said Frank. "It is going to boil over."
"Why didn't the water run over when it was cold?" asked Uncle Robert.
"The kettle didn't seem full then."
"Somehow it seems to get more than full when it boils," said Donald.
"See, it is boiling over."
Just then Jane took a pan of apples out of the oven. Each one looked
like a small volcano.

"What happens to the apples when they bake?" asked Uncle Robert.
"They just swell up so big their jackets won't hold them," said Donald,
laughing.
"It is heat that makes the bread rise, isn't it?" asked Frank.
"Of course," said Susie. "Don't you know sometimes if the bread
doesn't rise, mother says it is because it is too cold?"
"There is something besides heat that makes the bread rise," said Uncle
Robert.
"Yes," replied Susie, "the yeast; but it must be warm--I know it must."
"It seems as though everything is bigger when it is hot than when it is
cold," said Frank. "And now I believe I understand something that
happened not long ago."
"What was it?" asked Uncle Robert.
"Peter and I were driving to town," began Frank, "and the tire of one of
the wagon wheels slipped right off. We managed to get to the
blacksmith's shop, and he put the tire in the fire until it was hot. Then
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!"
"What will make it break?" asked Uncle Robert, pausing.
"Why, the hot water," said Susie.
"It always breaks glass if you put it in too quickly," said Donald.
[Illustration]
"Well, we'll warm it a little first," holding the bottle close to the water.
"I think I can try it now."
As he spoke he lowered the bottle into the water, and the rubber tied
over the neck began to bulge out.
"See!" cried Susie. "What makes it do that?"
"Try the cold now," said Uncle Robert. "Here, Donald, hold