y crowds into the space, from other parts of the room."

So he took a lamp from the table,--not the study lamp; it was a common
lamp,--and held it at various places in the opening of the fireplace, by
the jambs and near the upper part; and Rollo and Nathan saw that the
flame, in all cases, was turned in towards the chimney.

"Yes," said Rollo, "I see it is drawn in."

"No," said his father; "strictly speaking, it is not _drawn_ in; it is
pressed in, by the cool and heavy air of the room."

"I thought," said Rollo's mother, "that the chimney _drew_ the air from
the room into it."

"That is what is generally said," replied Mr. Holiday, "but it is not
strictly true. The common idea is, that the hot air rises in the
chimney, and so draws the air from the room to supply its place; but
this is not so. In the first place, nothing can rise unless it is forced
up. The lightest things have some weight, and would, if left to
themselves, fall. The hottest and lightest air in a chimney would fall
to the earth, if there was no cooler and heavier air around it, to force
it to rise;--just as the lightest cork, which would rise very quick from
the bottom of the sea, would fall back again very quick, if the water
was not there.

"Remember, then, Nathan and Rollo, that, when a fire is built in a
fireplace, so as to warm the air in the chimney, it makes this air not
so heavy; and then the cool air all around it in the room and out of
doors, presses in, and crowds under the light air, and makes it
ascend."

"But, father," said Nathan, "you said I might perform an experiment."

"Very well, I am ready now. Take the lamp, and carry it around the room,
and hold it opposite any little opening you can find."

"I can't find any little openings," said Nathan.

"O yes," said his father; "the key-hole of the door is a little opening,
and there is a narrow crevice all around the door; and you will find
little crevices around the windows. Now, hold the lamp opposite any of
these, and you will see that the air presses in."

So Nathan went with the lamp, Rollo following him, and held the lamp
opposite to the key-hole, and the crevices around the door and windows;
only, when he came to the window, his father told him to be very careful
not to set the curtain on fire.

Rollo wanted Nathan to let him try it once; and so Nathan gave him the
lamp. He said he meant to make a crevice; and so he pushed up the window
a very little way, and held the