"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.