"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 little carpet nail into each end of the strap. The strap, when it was nailed, passed directly across the clapper or valve. It was not drawn tight across, but it lay upon the clapper loosely. The ends were nailed tight, but the middle rested loosely upon the clapper. "Now," said Jonas, "I can push the clapper up a little way, but I can't push it far. The strap keeps it from coming up far." "But why," said Nathan, "do you want it to go up at all?" "To let the air in," said Jonas. "When I get the leather all nailed on again, I'll show you the whole operation of it." "And you can be telling us about it in the mean time," said Rollo. "Well, then," said Jonas, "when I lift up the upper side of the bellows by the handle, to blow, the air comes in by the hole. The clapper lifts up a little way, and lets it in. Then, when I press down the handle again, it presses the air out through the nose, because it can't go back through the valve hole." "Why not?" said Nathan.