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FIFTH BOOK.

SECTION I.

PHYSICAL GEOGRAPHY AND GEOLOGY.

ROTUNDITY OF THE EARTH.

A GREAT variety of appearances, both on the surface of the earth, and in the heavens, prove conclusively, that the earth is a spherical or round body.-1. When we stand on the sea-shore, while the sea is perfectly calm, we perceive that the surface of the water is not quite plane, but convex or rounded ; and if we are on the side of an arm of the sea, and, with our eyes near the water, look towards the opposite coast, we plainly see the water elevated between our eyes and the shore, so as to prevent our seeing the land near the edge of the water.—2. When an object is seen at a distance upon the surface of the earth, a part of its base is hid

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from the view. As the distance is lessened, a greater portion of the object becomes visible, and, when brought sufficiently near, the whole of it is seen. If, on the other hand, the distance is increased, the visible part of the body is continually diminished, and at last the object entirely disappears. Every person who has paid the slightest attention to the manner in which mountains, towers, and ships begin to appear and disappear, must be familiar with these facts.—3. Magellan, Drake, Anson, and other navigators, by holding an easterly or westerly course, at last arrived at the point of their departure. They, thus sailed upon a line, which, in one revolution, returned into itself, ending where it began; and, therefore, the surface on which it was described, must be a sphere, or must'resemble a sphere. This was further confirmed by the voyages of Captain Cook towards the south pole, from which it appeared that the course round the earth gradually diminished as it approached the pole.-4. When we travel a considerable distance from north to south, or from south to north, a number of new stars successively appear in the heavens, in the quarter to which we are advancing, and many of those in the opposite quarter gradually disappear, which would not happen if the earth were a plane in that direction.-5. All these proofs are confirmed and illustrated by eclipses of the moon, which present an ocular demonstration of the earth's rotundity. An eclipse of the moon is caused by the intervention of the body of the earth between the sun and the moon; in which case, the shadow of the earth falls

upon moon. This shadow is found in all cases, and in every position of the earth, to be of a circular figure; which incontrovertibly proves, that the whole mass of land and water, of which the earth is composed, is nearly of a globular form.

It may be objected that the earth cannot be of a spherical form, as its surface presents the most irregular appearances, being in innumerable places elevated into mountains, or depressed into valleys. But these irregularities bear no greater proportion to its whole bulk than a few grains of sand to a common terrestrial

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