CHAPTER XXXVII.
THE EARTH.
FORM OF THE EARTH—MOTION OF THE GLOBE—RATE AND MANNER OF PROGRESSION—LATITUDE AND LONGITUDE—THE SEASONS.
We have learnt from our books on Geography that the earth is shaped like an orange,—that is, our globe is round and flattened slightly at the “poles,” and we can easily see that the earth curves away, if we only try the experiment mentioned in a foregoing chapter—viz., how far a person standing (or lying) on the ground can see on a level. Our power of eyesight is not limited to three or four miles, but a man of ordinary height standing on the plain cannot see more than three miles, because the earth is curving away from him.
We know that at the seaside we can see ships gradually appear and disappear. When approaching us the masts and top-sails appear first, then the main-sails, and then the ship itself. A sailor climbing up the mast can see farther than the captain on deck, because he can see over the curve, as it were. When the vessel is at a considerable distance we see her “hull down” as it is termed,—that is, only her sails are visible to us, and at last they disappear also. If we want any other proof that the earth is round we can see when an eclipse takes place that the shadow on the moon is circular. So we may be certain of one fact; the earth is round, it is a globe. So much for the rotundity of the earth.
But the earth appears to us, except in very mountainous districts, as being almost a plane. This is because of its extent; and even from very high mountains we can only see a very small portion of the earth, and so, on a globe sixteen inches in diameter, the highest hills would be only about 1/100 of an inch, like a grain of sand.
The motion of the earth is known to most people, though as everything upon the globe passes with it, and a relative fixity is apparent, this is, of course, not real rest. The earth is moving from west to east at a tremendous rate,—viz., nearly nineteen miles a second! We think a train at sixty miles an hour a fast train; but what should we think of an express going more than 68,000 miles an hour! Yet this is about the rate at which our globe whirls around the sun. Her fastest pace is really 18·5 miles a second; the least about one mile per second less.
That is one motion of the earth; the other is its motion on its axis. If we send a skittle ball rolling we perceive it turns round as it proceeds. So the earth rotates on its axis, N S, in the accompanying diagram; the extremities of the axis are called the poles. The line in the middle is the equator, which is divided into 360 equal parts, each being 69-1/10 miles in length; so there are 180 lines, or rings, drawn upon the globe from N to S, and these are meridians. In England the degrees are calculated from the Greenwich meridian. We can thus obtain the distance of localities east or west, as we may briefly show (fig. 554).
