he took the bellows out
of Nathan's hand to look for it.

He found there was a corner, on the side opposite to the one where he
had been working, where the leather was open, he having forgotten to
nail it down.

"Ah!" said he, "here is the difficulty. When I have nailed this down, we
will try again."

"Is that a leak?" said Nathan.

"Yes," said Jonas. "When you worked the bellows, you pressed the air all
out through there. I did not know that that was open. Let me nail this
down, and then we will begin our experiment regularly."

QUESTIONS.

What was Jonas doing in the shop, when Rollo and Nathan went out
to find him? What part of the bellows was out of order? How did
he make a new valve? How did he fasten it to its place? Did he
nail down only one edge, or both edges? Why did he want the
other edge to be left at liberty? How did he prevent its lifting
up too far? What was the first experiment which he performed
with the bellows, after he had finished the mending? Did it
succeed at first? Why not? In working a pair of bellows, where
does the air come in? Where does it go out? Why cannot the air
escape through the valve where it comes in?

CHAPTER IV.

EXPERIMENTS.

When Jonas had finished nailing down the corner, he said, "Now there are
several experiments, which we can perform with the bellows. I will be
the professor, and you two shall be my class in philosophy, and I will
direct you how to make the experiments.

"First," said Jonas, "you, Rollo, may take hold of the nose of the
bellows with your hand, in such a way as to put your thumb over the end
of it, to stop it up, and then let Nathan try to blow."

Rollo did so, and Nathan tried to blow. He found that he could open the
bellows very easily; but when he attempted to press the sides together
again, he could not. He crowded the handle belonging to the upper side
down, as hard as he could, but it would not move.

"What makes it do so?" said Nathan.

"The air inside," said Jonas. "We have stopped up all the places, where
it could get out. The valve stops itself. Rollo stops the nose with his
thumb, and I have nailed the leather down close, about all the sides.
And so the air can't get out, and that keeps you from bringing the sides
together again."

Nathan tried again with all his strength. The sides came together very
slowly.

"They're coming," said he.

"Yes," said Jonas. "They come a lit