Geography. In this branch of geography, also, we begin by giving general views and leading ideas; and having traced the great outlines, we fill them up gradually, and in every thing that concerns Great Britain and Ireland, as minutely as practicable. At every step we apply the principles of CLASSIFICATION and COMPARISON. Mountains, rivers, lakes, states, cities, &c., are classed and compared ; which not only assists the memory of the pupils, but enables them to form correct conceptions of the real and relative magnitude of each. They are told, for instance, the height of a mountain, or the length of a river, with which they are familiar--or the population of the town in which they reside, and from these points the classifications and comparisons commence. The pupils are thus enabled to form correct and clear ideas of things which they do not know, by comparing them with things with which they are familiar. The largest river in Ireland is the Shannon-the largest in Europe the Volga; the length of the former is little more than 220 miles, of the latter about 2,200. It would take ten such rivers, therefore, as the Shannon, to make the Volga. Again, the highest mountains in Ireland are the Reeks in Kerry-in Europe, the Alps; the highest of the former (Carn Tual) is 3,410 feet above the level of the sea; of the latter (Mont Blanc), 15,744. The Alps are, therefore, nearly five times as high as the highest mountains in Ireland. Or, four such mountains as Carn Tual, piled on the top of each other, would not equal Mont Blanc in height and magnitude. What an idea this gives to children of the surpassing grandeur of Mont Blanc! And how their conceptions are enlarged, when informed that there are mountains in America and Asia nearly twice as high!

GEOGRAPHY, which, generally speaking, means a description of the earth, may be divided into three branches-namely, Mathematical, Physical, and Political.

MATHEMATICAL Geography, which treats of the form, motions, and magnitude of the earth, is connected with the sciences of Mathematics and Astronomy.

PHYSICAL Geography treats of the great natural divisions of the earth's surface; its material and structure; its various

productions, animal and vegetable; its atmosphere, climates. and other particulars respecting its physical or natural condition. This branch of Geography is connected with Natural History and Natural Philosophy.

POLITICAL Geography treats of the divisions of the earth into states and empires, with their extent, population, and resources forms of government, laws, religions, customs, manners, learning, and other matters which pertain to man, as a political or social being. This branch of Geography is, consequently, connected with History and Political Economy. The FORM of the earth is globular-that is, like a GLOBE or ball.

A teacher will be able to give his pupils a familiar, and tolerably correct idea of the form of the earth by directing their attention to the shape of an orange. After holding it up to their view, let him ask them if it is perfectly round like a globe or ball, and they will soon discover that it is a little flattened at the top and bottom. And So, it may be observed, the curved surface of the earth is a little flattened at the top and bottom; but not nearly so much in proportion to its size as an ORANGE.

The earth's surface, except where interrupted by elevations and declivities, appears to be flat, and not curved or globular; but this appearance is occasioned by the immense size of the earth. To a small insect, as a fly, creeping over an artificial globe its surface must appear flat, though we know that it is perfectly round or spherical; and so the surface of the earth appears to our bounded view. The tallest man, standing in the middle of the most extensive plain, cannot see the surface of the earth farther than three

*A GLOBE or SPHERE is a perfectly round body like a ball or marble. A SPHEROID differs from a perfect sphere by being either flattened about the top and bottom, like an ORANGE, or elongated like a LEMON. The former is called an oblate, and the latter a prolate spheroid. The word spheroid means like, or nearly a sphere.-See page 54.

b That is, about the POLES. The earth differs so little from a perfect sphere, compared with its great magnitude, that in any representation which we could make of it, the difference would be too small for perception. Hence, even the largest artificial globes are made perfectly round.

The earth's surface curves or slopes about eight inches in a mile, and this curvature increases with the square of the distance. Thus, in two miles the curvature is 4 times 8, or 32 inches; in three miles, 9

miles round him. But a circle on the earth's surface six miles in diameter is far less in proportion than a circle the size of a small wafer on the surface of an artificial globe. But such a circle, or even a much larger one, if cut out of the surface of an artificial globe, and laid upon the floor or a table, would appear to us to be flat, though we know that it is really globular, because it forms part of the surface of a globe. Thus it is plain that, although the portion of the earth's surface which we can see appears to be flat, yet the earth may, notwithstanding, be a globe. Nor do the mountains, or the other inequalities observable on the earth's surface, affect its general sphericity. If we examine the surface of an orange, we shall find it full of little inequalities, the least of which is greater, in proportion to the size of the orange, than the highest mountain on the earth's surface is to the magnitude of the earth. In fact, the smallest grain of sand on the surface of an artificial globe, twelve inches in diameter, would be larger, in proportion to such a globe, than the highest mountain on the surface of the earth would be to the great globe of the earth But oranges appear round and smooth notwithstanding the

times 8, or 72 inches; and so on, as the square of the distance. The eye of a man six feet high is not elevated 72 inches, or 6 feet above the surface, and therefore, in the position in which we have supposed him, he cannot see the surface three miles around him. Of course, he could see, at a much greater distance, objects that rise above the sur face, as houses, trees, and mountains.

For a similar reason, a small portion of the circumference of a circle if seen or viewed by itself, appears to form part of a straight line. It is only when a considerable portion of the circumference is seen that the curvature begins to appear.

a To represent in relief, and in relative proportions, the highest mountain in the world on the surface of an artificial globe twelve inches in diameter, we would require a grain of sand the 130th part of an inch in thickness-in fact, an almost imperceptible atom. For five miles, the height of, perhaps, the highest mountain in the world, is only about a 1600th part of the earth's diameter; and the 1600th of the diameter of a 12-inch globe is only about the 130th part of an inch.

On the surface of a large pincushion, in the form of a ball, the heads of the smallest pins that are made would be quite too large to represent the size of the highest mountains on the earth's surface, as compared with the great globe itself. And if the surface of such a pincushion were covered over with small pins, stuck up to the head, it would, if viewed from some distance, appear to be perfectly smooth or free from inequalities.

B

inequalities on their surface; and so would the earth, if we could see the half of it at one view, as we see the orange.

That the earth is a globe or sphere has been often proved practically. Several navigators have actually sailed round the world—that is, they have, by continuing their course to the westward, returned by the eastward to the place from which they set out, and vice versa; just as we may have seen a fly creeping down one side of an artificial globe and up the other.

MAGELLAN was the commander of the first expedition which circumnavigated the earth; but COLUMBUS first attempted it, and to him, consequently, the chief credit is due. Columbus, convinced in his own mind of the sphericity of the earth, concluded that he could reach the East Indies by continuing his course to the westward; and this he would have accomplished had not the world of which he was the discoverer intervened.

We shall now state briefly the arguments which led Columbus, and others long before his time, to conclude that the earth was a sphere or globe.

If the earth be a plain surface, extending out to the skies, as it appears to be, and as the uneducated still think it is, the sun and the other heavenly bodies would, when they rise above the horizon, be visible all over the world at the same time. But we know that this is not the case. To persons living to the eastward, the sun appears sooner than to persons living to the west; and we know that when the sun disappears below our horizon, he rises to countries west of us. This is occasioned by the curved or convex form of the earth's surface; just as a mountain, interposed between us and the rising or setting sun, intercepts him from our view.

It was this circumstance that first led the philosophers of antiquity to conclude that the earth was a spherical or round body. In proportion as they travelled eastward or westward, they observed that the sun rose sooner in the one case, and later in the other. They concluded, therefore, that the earth's surface, at least from east to west, must be globular. But they likewise observed that if they proceeded northward

a Hence the time of day as measured by the sun, can never be the same in places of which one lies either to the east or west of the other.