Page:On the various forces of nature and their relations to each other.djvu/29

Rh ball, which consequently assumed a shape very much resembling a flat cheese with round edges.] There you see a bubble of air bearing half a hundred weight, and you must conceive for yourselves what a wonderful power there must be to pull this weight downwards, to sink it thus in the ball of air.

Let me now give you another illustration of this power. You know what a pendulum is. I have one here (fig. 1), and if I set it swinging, it will continue to swing to and fro. Now, I wonder whether you can tell me why that body oscillates to and fro—that pendulum bob as it is sometimes called. Observe, if I hold the straight stick horizontally, as high as the position of the balls at the two ends of its journey