A VOYAGE IN SPACE
Well, then! we may accept this fact that all bodies, even the tiniest little particles, are pulling as hard as they can, though particles cannot do much. It is only when a great crowd of them are massed together to make the Earth that the pull becomes easy to feel. And when we get an enormously greater crowd still, such as the Sun, the pull is enormously greater. Why, then, does not the Sun pull us away from the Earth? Well, there is more than one reason; but one at least is that he is so much farther away, and this brings us to the next fact we have to notice about Gravity—that it depends on the distance.
A body close to you pulls hard: take it farther away and the pull becomes less. Mathematicians say that it diminishes as the "inverse square of the distance"; but we can put the law into simpler language in this way. Take a body twice as far away, and the pull is one quarter of what it was; bring it twice as near, and the pull is four times what it was. And now let us go back to the history of the discovery and see how Newton found this out for us.
About the time when Galileo lived in Italy, there was another wonderful man called Tycho Brahe, living in Denmark, who also mistrusted some of the things told him on good authority. For instance, there were books giving the positions in which the planets ought to be seen at any time, which were still trusted although the planets could be seen not to follow the books. Tycho determined to go to work for himself, observing carefully the movements of the planets with the idea of making better books or tables than those in use. A beautiful observatory