shing of the room. He said he could not find any
place.

His mother then told him to hold his tuft down near the bottom of the
door-way. He did so, and found that the current of air was there very
strong. The tuft swung into the room very far.

"Now hold it up a little higher," said his mother.

Rollo obeyed, and he found that it was still pressed in, but not so
hard.

"Higher," said his mother.

Rollo raised it as high as he could reach. The thread was of such a
length, that the tuft hung about opposite to his shoulder. The tuft was
still pressed in, but not nearly as far as before.

"So you see," said his mother, "that the air pours in the fastest at the
lowest point, where the weight and pressure of the air above it are the
greatest; just as, in your dam, the water from the lowest holes spouted
out the farthest."

"Yes," said Rollo, "it is very much like that."

"Now," continued his mother, "you see that a great deal of air comes in,
and if you look up chimney, you will see that there is scarcely room for
so much to go up there;--and yet just as much must go out as comes in.

"Get the step-ladder," said his mother, "and stand up upon it, and so
hold your tuft in the upper part of the door-way."

There was in the china closet a small piece of furniture, very
convenient about a house, called a step-ladder. It consisted of two
wooden steps, and was made and kept there to stand upon, in order to
reach the high shelves. Rollo brought out the step-ladder, and placed it
in the door-way, and then ascended it. From the top he could reach
nearly to the top of the door; but then, as his tuft was at the end of
the thread, it hung down, of course, some little distance below his
head.

"Why, mother," said Rollo, "it goes _out_."

"Yes," repeated Nathan, "it goes out."

In fact, Rollo found that the tuft, instead of swinging into the room,
was carried out towards the entry.

"You have found out, then," said his mother, "where the hot air of the
room goes to, to make room for the cold air, that comes in from the
entry."

"Yes, out into the entry," said Rollo.

"Through the upper part of the door," said his mother. "Suppose the
entry were full of water, and the parlor full of air, and the door was
shut, and the door and the walls were water-tight. Now, if you were to
open the door, you see that the water, being heavier, would flow in,
through the lower part of the door-way, into the parlor, and the air
from the