but he did not know what it was for.

"What is the hole for?" said Nathan.

"That is to let the air in," said Jonas.

"What do they want the air to come in for?" said Nathan.

"To make wind of," said Jonas.

"Do they make wind out of air?" said Nathan.

"Yes," said Jonas, "they get the bellows full of air, and then blow it
out through the nose, and that makes wind."

"Wind is air, put in motion," said Rollo. "I read it in a book."

By this time, Jonas had taken off the leather so far that Nathan could
see into the bellows. He saw that there was a little clapper over the
hole, in one of the sides of the bellows.

"Is that the valve?" said he to Jonas.

"Yes," said Jonas.

"What is it for?" said Nathan.

"It is to keep the wind from coming out of that hole."

"Why don't they want the wind to go out of that hole?" said Nathan.

"Because," said Jonas, "they want it to go to the fire,--to blow the
fire."

"You see," said Rollo, "it can't go out of the hole, and so it has to go
out of the long nose, which is pointed towards the fire."

"What makes it go out at all?" said Nathan.

"Why, when we blow the bellows, we press the two sides together, and
that presses the wind out. It can't go out of the hole whence it came
in, because the clapper stops it up, and so it goes out the long nose,
right into the fire, and makes the fire burn."

By this time, Jonas had got the leather off so far, that he could get at
the clapper to mend it. He told the boys that it was old and worn out,
and he must make a new one.

"How are you going to make it?" said Rollo.

"You'll see," said Jonas, "if you watch me closely."

So Jonas took some leather, and cut out a piece, of an oblong shape, a
little wider than the hole, and about twice as long. Then he laid this
down over the hole. It covered it entirely. Then he took some small
carpet nails, and nailed one of the ends of the leather down to the
board. Then Jonas put his hand down under the board, and run one of his
fingers up through the hole, and pushed the leather up a little way.

"There," said he to the boys, "you see I have nailed the leather, so
that, when it lies down in its place, it covers the hole completely; and
yet I can push it up a little with my fingers, so that there will be an
opening."

Then Jonas cut a small leather strap, and nailed one end of it down upon
one side of the clapper, and the other end upon the other side of the
clapper. He put one littl