Pa. 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, everything of which the world is composed, draws toward 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 everything 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, everything 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 anything, 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?
Lu. I think I do. It is like a loadstone drawing a needle.
Pa. 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 everything alike.
Lu. Then it is pulling you and me at this moment.
Pa. It is.
Lu. But why do not we stick to the ground, then?
Pa. 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 limits the force of your jump, and brings you down again after that force is spent.
Lu. 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 toward 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.
Pa. Very true. And whither should they fall? What have they over their heads?
Lu. I don’t know; sky, I suppose.