But to resolve this problem with a machine that represents the effect of mus cles better than did the one just given, we blow slightly into a balloon and then put a stone weighing or hundredweight on this half inflated balloon; or, having laid it on a table, cover it with a board and cover the board with a large stone, or make a very heavy man sit down on this board, even allowing him to keep hold of something in order to resist the swelling of the balloon; for if someone blows anew into this balloon, even with the unaided mouth, it will raise the stone that compresses it or the man sitting on it, provided the channel through which the wind enters the balloon