Why Doesn’t it Stop?

It goes till it is stopped. There is in the window of a store on Post Street, between Montgomery and Kearney, a small apparatus constructed almost entirely of glass that is attracting a great deal of attention, and there is not one who looks at it but exclaims: “Perpetual motion!” The inventor of the apparatus is C. F. A. Sturts, who is a practical watchmaker. “I do not call it perpetual motion,” he said yesterday; “it is only an illustration of a scientific problem, but it is as near as perpetual motion will ever be reached. As you can see, the apparatus rests on glass uprights. It is in the shape of a hub with eight arms or spokes, as you might term them. The whole is one piece of glass; the arms, which are hollow cylinders, are part of the hub. The outer ends of the cylinders are solid, but at the inner end there is a small opening. In each cylinder there are two highly polished steel balls a quarter of an inch in diameter, as round as human ingenuity can make them, and each of the same exact weight. The shaft which rests up on the upright is also part of the wheel. When the wheel had been constructed and the balls put in place the air was extracted, just as the air is extracted from an electric light bulb. The reason of this was to allow the little balls to roll in the cylinders without resistance. The little machine was set perfectly level and allowed to turn. The principle is gravity, and the wheel will keep on running until I stop it,” said Mr. Sturts to the San Francisco Call representative. “I will add that it has no power, but just enough to move itself, and that it is not moved by electricity, magnetism or any other outside force.”