In your dam, for instance, when it
was full, you had water on one side of the board, and no water on the
other; and then, by opening a hole in the board, the water spouted
through; but we cannot very well get air on one side of a partition, and
no air on the other; if we could, it would spout through very much as
the water did."

"Why can't we do that, sir?" said Rollo.

"Because," replied his father, "we are all surrounded and enveloped with
air. It spreads in every direction all around us, and rises many miles
above us. Whereas, in respect to water, you had one little stream before
you, which you could manage just as you pleased. If you were down at the
bottom of the sea, then the water would be all around you and above you;
and there, even if you could live there, you could not have a dam."

"No, sir," said Rollo, "the water would be everywhere."

"Yes," replied his father, "and the air is everywhere. If, however, we
could get it away from any place, as, for instance, from this room, then
bore a hole through the wall, the weight of the air outside would crowd
a portion of it through the hole, exactly as the weight of the water
above the board in your dam crowded a part through the hole in the
board."

"I wish we could try it," said Rollo.

"We _can_ try it, in substance," said his father, "in this room; or--no,
the china closet will be better."

There was a china closet, which had two doors in it. One door opened
into the parlor, where Rollo and his father were sitting. The other door
opened into the back part of the entry. Rollo's father explained how he
was going to perform the experiment, thus:--

"If we could, by any means, get all the air out of the closet for a
moment, then the pressure of the air outside would force a jet of it in
through the key-holes of the doors, and the crevices."

"And how can we get the air out?" said Rollo.

"We can't," said his father, "get it all out; but we can get a part of
it out by shutting the door quick. The door will carry with it a part of
the air that was in the closet, and then the outside air will be spouted
in, through the key-hole of the other door. Only we can't see it, as we
can the water."

"No," said Rollo; "but I can put my hand there, and feel it."

"A better way," said his father, "would be to hold a lamp opposite to
the key-hole, and see if it blows the flame."

Rollo tried the experiment, in the way his father had described. He went
into the close