15
we see lower portions of them, and finally their bases, and the face of thecountry.
The scene exhibits these effects, where the figures of the ships are shewn tobecome respectively more and more curtailed in their apparent height above thesurface of the sea, as their distance from the spec tator increases. Of thedistant ship he secs only the upper parts of the masts; of the next nearerto him he sees the lower parts of the masts and rigging ; hut of the ship at thenearest point of distance, he sees, not only the masts entirely, hut the hull ofthe vessel itself, down to the surface of the water on which it floats, togetherwith that portion of the surface which lies between the object and himself; ofthe ship more remotely placed, he sees nothing. These are appearances whichcan only be reconciled by assuming a spherical figure for the earth. The sameconclusion may be drawn from observing the altitude of the pole star at differentstages of a considerable journey towards the north or south. In travellingnorthward its altitude is increased ; in travelling south, it is diminished. Fur-ther proof of the spherical form of the earth is obtained from its shadow in aneclipse of the moon.
But the most popular proof of the rounded figure of the earth is obtainedfrom the well-known fact, that navigators have actually sailed round it; not onan exact circle it is true, because the irregular figure of the shores does not admitof such a course, but by keeping the direction at first assumed, as nearly asaccidental interruptions allowed, they have uniformly arrived at the port fromwhich they departed. Drake, Anson, and Cook, are familiar to all readers,as circumnavigators; those who, in the common mode of expression, “ per-formed voyages round the world.” Some of these have sailed in an easterlydirection, others in a westerly, and we find that each, by keeping the samegeneral course, has again arrived at the point of departure; and that they all,in the progress of their voyages, observed the phenomena now described, andthus confirmed the opinion that the earth is of a spherical form.
Although these observations, respecting the figure of the earth, affordsufficient evidence that its surface is curved, and its form of globular character,yet none of them determine scientifically, or entitle us to infer, that it is aperfect sphere. It was natural for those who first discovered that the earthhad, to our common observation, a character of sphericity, to suppose that itsform was spherical in perfect strictness. This, however, is now known notto he the case ; the true figure being that of a sphere, in a small degreeflattened at the two poles, or what is termed an oblate spheroid.