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P. But why must it fall—that is the point.
L. Because it could not help it.
L. I don't know—that is an odd question. Because there was nothing to keep it up.
P. Suppose there was not-does it follow that it must come
to the ground ?
L. Yes, surely!
P. Is an apple animate or inanimate?
L. Inanimate, to be sure !
P. And can inanimate things move of themselves ?
L. No—I think not-but the apple falls because it is forced to fall.
P. Right! Some force out of itself acts upon it, otherwise it would remain for ever where it was, notwithstanding it were loosened from the tree.
L. Would it?
P. Undoubtedly! for there are only two ways in which it could be moved ; by its own power of motion, or the power of somewhat else moving it. Now the first you acknowledge it has not; the cause of its motion must therefore be the second. And what that is, was the subject of the philosopher's inquiry.
L. But every thing falls to the ground as well as an apple, when there is nothing to keep it up.
P. True-there must therefore be a universal cause of this tendency to fall.
L. And what is it ?
P. Why, if things out of the earth cannot move themselves to it, there can be no other cause of their coming together than that the earth pulls them.
L. But the earth is no more animate than they are : so how can it pull ?
P. Well objected! This will bring
us to the point. Sir Isaac Newton, after deep meditation, discovered, that there was a law in nature called attraction, by virtue of which every particle of matter, that is, every thing of which the world is composed, draws towards it every other particle of matter, with a force proportioned to its size and distance. Lay two marbles on the table. They have a tendency to come together, and if there were nothing else in the world, they would come together, but they are also attracted by the table, by the ground, and by every thing besides in the room; and these different attractions pull against each other. Now, the globe of the earth is a prodigious mass of matter, to which nothing near it can bear any comparison. It draws, therefore, with mighty force, every thing within its reach, which is the cause of their falling: and this is called the
gravitation of bodies, or what gives them weight. When I lift any thing, I act, contrary to this force, for which reason it seems heavy to me, and the heavier, the more matter it contains, since that increases the attraction of the earth for it. Do you understand this?
L. I think I do. It is like a loadstone drawing a needle.
P. Yes-that is an attraction, but of a particular kind, only taking place between the magnet and iron. But gravitation, or the attraction of the earth, acts upon every thing alike.
L. Then it is pulling you and me at this moment?
P. It is.
L. But why do not we stick to the ground then?
P. Because, as we are alive, we have a power of self-motion, which can to a certain degree overcome the attraction
of the earth. But the reason you cannot jump a mile high as well as a foot, is this attraction, which brings you down again after the force of your jump is spent.
L. I think then I begin to understand what I have heard of people living on the other side of the world. I believe they are called Antipodes, who have their feet turned towards ours, and their heads in the air. I used to wonder how it could be that they did not fall off; but I suppose the earth pulls them to it.
P. Very true. And whither should they fall ? What have they over their heads ? · L. I don't know; sky, I suppose.
P. They have. This earth is a vast ball, hung in the air, and continually spinning round, and that is the cause why the sun and stars seem to rise and