"Because," said Jonas, "the valve falls down over the hole, and stops it up. It is made so as to lift up easily, and then to fall down and cover the hole exactly, and prevent the air going out the same way it came in. So, as it cannot get out by the valve, it has all to go out through the nose. If the nose were stopped up, it could not get out at all." "And what then?" said Rollo. "Why, then," replied Jonas, "you could not bring the two sides of the bellows together again. The air between would keep them apart." "I should like to try," said Rollo. "Well," said Jonas; "and there are some other experiments you may perform with it too." At length, Jonas said that he had got the leather all nailed on, and they might try the experiment. He took hold of the nose of the bellows, and held his thumb near the end of it, ready to stop up the hole. "Now, Nathan, you may take hold of the handles, and pull them apart as if you were going to blow." Nathan did so. He pulled the handles apart, and held them open. "Now," said Jonas, "I will stop up the nose, and the valve will close itself; and then you will find that you cannot bring the sides together again." So Jonas put his thumb over the hole, and told Nathan to blow. Nathan pressed hard, and the sides came together again, about as easily as usual. "What!" exclaimed Jonas with surprise. He did not know what to make of the failure of his experiment. "There must be a leak somewhere," said he. And 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.