And the reason why he cannot is that he is too heavy. He is too heavy in America: and he is too heavy in Australia. In both cases he is heavy _towards the ground_: and he cannot get away from the ground without something to bear him up. It is just as impossible that people in Australia should drop off the world into the sky as that people in America should do so. But--you will perhaps say--the sky is _above_ us here; and in Australia it would be _under_ us. Oh, no; it would not! The sky is all round the whole Earth, on every side alike. In all parts of the world people have the sky over their heads and firm ground beneath their feet. The Australian sky is under the feet of those who live in North America: that is true. But then it is no less true that the North American sky is under the feet of those who live in Australia. To you the Earth is underneath: the sky is overhead. To an Australian also the Earth is underneath and the sky is overhead. All round the world it is the same. _Down_ means always towards the ground. _Up_ means always towards the sky. If you hold up a stone in the air, and let it go, what happens? The stone drops at once to the ground. If you fling a ball into the air, what happens? The ball goes a little upwards, carried by the force of your fling: but soon it curves over and comes to the ground. If you tilt up a jug full of water, what happens? The water pours down upon the floor. If a man steps over a precipice-edge, what happens? He falls to the bottom, and is most likely killed. But these things are not more true of the United States than of Australia. All round the world, in every part, it is the same. Water always flows downward. Loose bodies always drop downward, unless kept up by something. We have been asking why it is that people never drop off from the Earth into the sky. Of course nobody ever asks that question about the part of the Earth on which he happens to be. Whether he is in England, or in America, or in Australia, he knows very well that _he_ is in no danger of “dropping off.” The very idea as to himself would seem absurd. To “drop off” would really be to rise upward into the sky: and he feels that he is much too heavy for that. It is only when he thinks about the other side of the world, and about people walking there with their heads hanging downward---- But they do _not_ walk with their heads hanging downward. Their heads, like ours, point upward to the sky; and their feet, like ours, rest firmly on solid ground; and they too, like us, are heavy towards the Earth. It is as impossible for a man in Australia as for a man in England or America to “drop off” the Earth--in other words, to rise upwards towards the sky. His own weight holds him down. What do we mean by “weight?” What makes a man “heavy?” He is made heavy by the Earth’s pulling or attracting him; and this gives him weight. And how does the Earth pull?