The reason that we do not see that the earth is round is that we are so small and the earth is so large. We see that a globe is round, but it probably seems flat to any little fly that lights upon it, just as the earth does to us.
What is up and what is down.
You can see, then, that as the earth is round, what is down to people on the other side of the earth is up to us. If a boy there throw up a ball at the same time that you throw up one here, the two balls fall toward each other when they come to the ground.
Figure illustrating this.
What we call down, then, is simply toward the ground, or, rather, it is toward the middle of the earth, for we say down in a well or down in the ground. Indeed, if any thing could keep on in the same line in which it falls, it would go right to the centre of the earth. If the ball which you throw up and the ball thrown up by a boy on the other side of the earth should keep on in the ground in the same direction that they fall, they would meet exactly at the earth’s centre. This is represented in this figure. The circle represents the round earth. The lines drawn from the two falling balls to the middle of the circle show how they would come together at the centre of the earth if they could keep on, instead of being stopped when they reach the ground. And all the things that are falling any where on the earth are going toward the same point.
Now why is this? What is it that makes things in the air come to the ground when they are not held up? They do not come down of themselves. They are drawn down. The earth attracts or draws them. How it does this we do not know. We can not see how it is done, but the earth does it as really as if we could see it put up a hand and pull things down.
Attraction not a thing that we can see.
There are other kinds of attraction that operate in a way that we can not see nor understand. There is the attraction of magnetism. If, as I have told you in the last chapter, you bring a magnet toward a piece of iron or steel, for example a needle, when you get it quite near, all at once the needle will go to the magnet and stick to it. You can not see any thing between the magnet and the needle to draw the needle to it. You only know that the needle is drawn or attracted, but you do not know how this is done.