The right name for a globe-shaped body, like an orange or like the Earth, is a “sphere.” Neither an orange nor the Earth is a _perfect_ sphere, because both have flattened ends; still, the ends are only a little flattened, and we always speak of the Earth as a “sphere.” A “hemisphere” means a “half-sphere.” If our whole Earth were cut into two equal-sized pieces each of those pieces would be a “hemisphere.” We always think of the equator as dividing our Earth into two halves. The half towards the north is called “the northern hemisphere;” and the half towards the south is called “the southern hemisphere.” Since our Earth is said to be a round globe, like a ball, why do we not see over the edge? A fly, standing on an orange, would have, it is true, a rounded surface just under his feet; but he could take a good view downward over the edge. It would _look_ like an edge to him, though there is no edge really to a ball. If our world were as small as an orange, and we by comparison were each as large as a fly, then we should be able to do the same. But the Earth is huge in size: and we are very tiny--yes, exceedingly tiny, side by side with the great Earth! And the surface on which we stand curves away so very gently, so very gradually, that it looks like a flat surface to us--just as the large globe would have seemed flat to the wee red spider, only very much more so. For the difference in size between the Earth and a man is far greater than the difference between the globe and the spider. You may get some idea of how things are, by standing on the sea-shore, and gazing out to sea. Far away the sky and earth seem to meet in a long line, which we call “the horizon.” That line is always around you, on all sides, wherever you are, though often you cannot see it, because of hills or buildings or trees coming between. Beyond that line the rounded surface of the Earth _drops_ away, so that you can see it no more. It is, in fact, what looked like an _edge_, to the fly standing on the orange. To us it looks much more as if the ground slanted upwards to meet the sky. But there is no real upward slant. After a certain number of miles, the surface of the ground or the ocean dips downward, out of sight, and all else beyond that line is out of sight also. Put your eyes close down upon a large schoolroom globe. You will see at once how the solid ball hides from you part of the room. You can see the ceiling, and perhaps the window and the fireplace, but beyond the globe all is hidden. Your _horizon_, as you stand thus, is just where you seem to see a sort of edge to the globe, beyond which its rounded surface dips away, out of view. Looking upward into the sky we are able to see enormous distances--hundreds of miles, thousands of miles, millions of miles, billions of miles away! Light travels to earth from far, far distant stars: and we can perceive those feeble gleams because nothing comes between to hide them.