Page:Various Forces of Matter.djvu/27

Rh myself, sensible that these balls did attract one another; and yet we know that such is the case, because if, instead of taking a small ivory ball, we take a mountain, and put a ball like this near it, we find that, owing to the vast size of the mountain, as compared with the billiard ball, the latter is drawn slightly towards it; showing clearly that an attraction does exist, just as it did between the shell-lac which I rubbed and the piece of paper which was overturned by it.

Now, it is not very easy to make these things quite clear at the outset, and I must take care not to leave anything unexplained as I proceed, and, therefore, I must make you clearly understand that all bodies are attracted to the earth, or, to use a more learned term, gravitate. You will not mind my using this word, for when I say that this penny-piece gravitates, I mean nothing more nor less than that it falls towards the earth, and if not intercepted, it would go on falling, falling, until it arrived at what we call the centre of gravity of the earth, which I will explain to you by and by.

I want you to understand that this property of gravitation is never lost, that every substance