Page:On the various forces of nature and their relations to each other.djvu/36

32 with, and run a bradawl through it at one corner (fig. 3), and Mr. Anderson hold that up in his hand before us, and I then take a piece of thread and an ivory ball, and hang that upon the awl—then the centre of gravity of both the pasteboard and the ball and string are as near as they can get to the centre of the earth; that is to say, the whole of the attracting power of the earth is, as it were, centred in a single point of the cardboard—and this point is exactly below the point of suspension. All I have to do, therefore, is to draw a line,, corresponding with the string, and we shall find that the centre of gravity is