Pབབབ་

to their own advantage by asserting th were kept upright by means of sacrifices (Fig. 7).

Earthquakes were thus ascribe

The

off of sacrificial subscriptions. represented the earth as a hemisphe by four elephants standing upon the tortoise (Fig. 8). But this, to a great be allegorical, the elephants represent cardinal points, while the tortoise symbol or eternity. Anaximander taught tha was drum-shaped, with only the top

inhabited. This world was supposed to rest upon compressed air, but what was beneath the air was left out of the question. The earth has also been imagined to be cubical-like a dice-egg-shaped, and triangular; but the general opinion for ages was that it was flat, that the visible horizon-the line where earth and sky appear to meet-marked the bounds of the earth, that the heavens and earth above the ocean represented the whole creation, and that all below the ocean was Hades.

One of the most apparent indications that the surface of our globe is curved is afforded by the form of the surface of the sea. Nine hundred years before the commencement of our era, Homer remarked that the sea was convex, but in spite of this, both he and the writers of his day believed the earth to be a circular plain surrounded by an ocean stream. A clear proof that the earth is more or less globular in shape is deduced from the fact that the horizon is always bounded by a circle. This outline cannot usually be traced upon the land, on account of local depressions and elevations, but on the sea, where nothing interrupts the view, the distance of the boundary of vision is the same in every direction. This distance, however, increases with the height of the observer above the sea surface (Fig. 9). Every boy knows that a whaling vessel has a crow's nest" fixed high up on one of its masts, in which a seaman looks out for the monster of the deep. The mariner thus stationed has a much more extended view than his fellows. He is able to see beyond their horizons, and so often catches sight of objects to them invisible. The visible horizon, then, is a circle. At the equator, in the Antarctic, or in

FIG. 9.-A clear proof that the earth is more or less globular i from the fact that the horizon is always bounded by

sink out of sight. Were the earth a an outward-bound vessel would graduall The rigging and masts would first beco and the hull would be seen long after t appeared. But the reverse is found to On a clear day, at the seaside, a small show the topmasts of ships rising above while the lower parts are quite out of sig Evidently a flat surface is at variance simple observations. The existence of a cu

and of a curved surface only, will explain the facts.

It

is rather unfortunate, however, that most elementary books on geography, and many dealing with astronomy, should quote the sinking of ships below the horizon as a proof that the earth is a globe, whereas it only indicates that the surface is curved.

FIG. 10. The fact that an outward-bound ship appears to sink below the horizon indicates that the earth's surface is curved.

The fact that the earth has been circumnavigated is also generally stated to be a proof of its globular form. There are still a few people who believe the earth is flat, and to them the credit is due of having found out all the weak points in the arguments against their view. Circumnavigation has been effectually disposed of. We know that by continuing on a due east or due west course for a long enough period of

time, a vessel returns to the place from which she started, and we say she has sailed round the world. The proper direction is determined by observations of the position of a compass needle. Now, suppose we lived upon the flat surface of an earth shaped like a Cheddar cheese; and suppose, also, that a compass needle always set itself in the direction of a line drawn from the centre of the surface to the outer edge, with the North Pole pointing towards the centre. A vessel sailing due east or west under such circumstances would describe a circle round the centre, and so would return to the starting-point. It would have circumnavigated the earth.

Two facts known to the ancients prove indisputably that the earth is nearly, if not quite, spherical. One is the appearance of the moon when she is eclipsed. From time to time the full moon passes into a shadow and loses its light for a couple of hours. The outline of the shadow which appears on the lunar disc, is always circular (Fig. 11). This is a very important circumstance. Only one figure throws a round shadow under all conditions, and that is a globe. The shadow into which the moon passes must therefore be the shadow of a large ball. Early astronomers knew that an eclipse of the moon was caused by the moon entering the shadow of the earth. With this knowledge, and the facts of observation, it was possible to place the carth's globularity beyond the possibility of doubt.

Another fact which results from the earth's spherical form is that the same stars have different altitudes when observed from different latitudes. If the earth were flat, the altitudes of stars would be the same from whatever place they were viewed, but the