UNIVERSAL GEOGRAPHY.

Divisions of the Science.] GEOGRAPHY, a name derived from two Greek words signifying a description of the earth, is the science which treats of the form and physical features of the globe. As the earth may be either considered with relation to the planetary system of which it forms a part, or as a distinct body, possessed of peculiar features or qualities, and exhibiting peculiar phenomena,-or as the abode of rational men, who have apportioned out its surface into various artificial divisions, so there are three great divisions of the science itself: viz. Mathematical, Physical, and Political Geography. The general principles of Geography arrange themselves into these three departments, the knowledge of which ought to precede the study of particular facts.

GENERAL GEOGRAPHY.

PART I.-MATHEMATICAL GEOGRAPHY.

Various subjects which the science of geography embraces, require for their investigation the aid of mathematical reasoning. Among these subjects are the figure and magnitude of the earth, the methods of determining the relative position of its different parts, or the latitude and longitude, the relation of the earth to the other bodies of the universe, and particularly the mode in which it is illuminated by the sun,—the divisions which have been made of the earth's surface upon astronomical and mathematical principles, and the different methods of representing that surface, whether by artificial globes or maps. department of geographical science, therefore, in which these and similar subjects are treated of, has received the appellation of Mathematical Geography.

The

Almost all the different parts of mathematical geography reflect light upon each other; and it is therefore difficult to obtain such an arrangement as may enable us at once fully to discuss any one of them, while the others are not understood. Thus, before explaining the methods of determining the relative position of places upon the earth, it is proper that we should be acquainted with its figure; while, without understanding some of the appearances which the heavens present, and which it will be necessary to explain in considering the latitude and longitude, that figure cannot be exactly determined. In this department of science, therefore, it is sometimes absolutely necessary only partially to explain a subject at first, and to reserve the more complete investigation of it until other subjects have been considered.

Rotundal Figure of the Earth.] We shall begin with explaining the figure of the earth, and, for the reasons that have been stated, notice

here only some phenomena from which a general idea of that figure may be obtained.

When we take a cursory view of the appearance of the earth, it seems to be merely a vast circular plain. By a slight degree of attention, however, to such phenomena as the following, its rotundity will in a familiar manner be completely established.

Proofs.] 1st. If when standing upon the sea-shore, or on the banks of a river of considerable breadth, we examine the appearance which the surface of the water presents, it will be distinctly seen to be curved.

2d. When an object is seen at a distance upon the surface of the earth, a part of its base is hid from 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 be 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 those facts. Now were the earth a plane, bodies would simply diminish in apparent magnitude as their distance from us was increased, without any part of them being hid from view. The phenomena in question, therefore, clearly prove, that the plane in which bodies appear to be placed, is really a convex surface, which intercepts the light reflected by distant objects, and prevents it from reaching the eye of the observer.

3d. As we ascend a tower or a mountain, our view becomes gradually more extended. There could be no such extension of view were the earth a plane.

4th. When we change our position on the surface of the earth, moving south or north, a number of stars, which never were visible in the place we formerly occupied, gradually appear, while others in the opposite direction, that were constantly to be seen, are disappearing from view. Every other star in the heavens, too, appears altered in position. These appearances also evidently prove the convexity of the earth.

5th. All the phenomena which we have noticed, occur in apparently the same uniform degree in every part of the earth. This proves not only that the earth is a curved body, but also that it is nearly of uniform curvature, or a sphere.

6th. Another proof of the rotundity of the earth is derived from the many voyages which have been performed around it. Magellan and his successors, pursuing constantly a western or eastern course, have at last returned to the place from whence they set out. It is evidently impossible that they could have so returned had the earth been a plane.

7th. Astronomers show that eclipses of the moon are occasioned by the earth intercepting for a while the moon's light from the sun. Now the portion of the moon's disk of which the light is intercepted has always a circular form: the earth, therefore, must be of a spherical figure, for a spherical body only can in every position project a circular shadow.

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 when compared with the immense magnitude of the earth are very inconsiderable. The height of the highest mountain does not exceed 29,000 feet, while the diameter of the globe, as we shall afterwards see, is more than 8,000 miles.

From the obvious appearances, therefore, which have been noticed, we are entitled to conclude that the form of the earth must be at least nearly spherical. This truth being established, we shall next consider the relation of the earth to the other great bodies of the universe. After this and some other subjects have been explained, we shall resume consideration of the figure of the earth, and inquire how far it deviates from an exact sphere.

Relation of the Earth to the System of the Universe.] It belongs to astronomy to explain the motions, magnitudes, and distances of the heavenly bodies, and the physicial laws by which the movements of these bodies are carried on; but it seems to be necessary in a work which treats of the science of geography, slightly, at least, to notice the place which the earth occupies in the great system of the universe. To this subject, therefore, and the mode in which the earth is illuminated by the sun, we shall now proceed.

The Visible Horizon.] If we place ourselves on the top of a tower, or in the midst of a large plain, the heavens will seem to be a vast hemisphere supported upon the earth. The circle in which the earth and heavens appear to meet, is termed the visible horizon.

Motion of the Stars.] If we attentively examine the motions of the stars, they will be found to rise at different points of the horizon, to move in plains parallel to each other, and to set at points more or less distant from those at which they arose. It will also be found that they constantly preserve the same relative distances in regard to each other: always rising and setting at the same points of the horizon, and moving in the same plains, so that the starry vault appears to turn tout d'une piece round the earth. A revolution of the stars is accomplished in rather less than twenty-four hours. The magnitude of the circles in which the stars appear to move, gradually dminishes as we advance towards the north, and at last dwindles to a point.

Cardinal Points.] It is necessary here to remark, that the north and south points are those in which the horizon is cut by a circle perpendicular to it, and passing through the point of the heavens which remains stationary, and the place of an observer. Another circle, perpendicular to the last, and also passing through the place of an observer, will indicate by its intersections with the horizon, the east and west.

Apparent Motions of the Sun.] On attending to the motions of the sun, it will be seen that that luminary, besides its apparent diurnal motion round the earth, along with the other heavenly bodies, daily changes its position in relation to the stars in a twofold manner. First, it does not, like them, always rise and set at the same points of the horizon; but, in a gradual manner, alternately advances to and recedes from the north. In the second place, it has a motion also towards the east, for the stars which on any particular day are seen setting immediately after it, will in a few days, appear rising before it, and their rising will daily more and more precede that of the sun. After the lapse of a year, having apparently made a complete circuit among the stars, the sun will seem to have returned to its former relative position. Astronomers, in order the better to estimate this apparent motion of the sun, referred it to the groups of fixed stars, termed constellations, through which the sun appears necessarily to pass. Zodiac and its Signs.] These constellations, which are twelve in number, are also denominated signs; and the zone of the heavens in

here only some phenomena from which a general idea of that figure may be obtained.

When we take a cursory view of the appearance of the earth, it seems to be merely a vast circular plain. By a slight degree of attention, however, to such phenomena as the following, its rotundity will in a familiar manner be completely established.

Proofs.] 1st. If when standing upon the sea-shore, or on the banks of a river of considerable breadth, we examine the appearance which the surface of the water presents, it will be distinctly seen to be curved.

2d. When an object is seen at a distance upon the surface of the earth, a part of its base is hid from 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 be 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 those facts. Now were the earth a plane, bodies would simply diminish in apparent magnitude as their distance from us was increased, without any part of them being hid from view. The phenomena in question, therefore, clearly prove, that the plane in which bodies appear to be placed, is really a convex surface, which intercepts the light reflected by distant objects, and prevents it from reaching the eye of the observer.

3d. As we ascend a tower or a mountain, our view becomes gradually more extended. There could be no such extension of view were the earth a plane.

4th. When we change our position on the surface of the earth, moving south or north, a number of stars, which never were visible in the place we formerly occupied, gradually appear, while others in the opposite direction, that were constantly to be seen, are disappearing from view. Every other star in the heavens, too, appears altered in position. These appearances also evidently prove the convexity of the earth.

5th. All the phenomena which we have noticed, occur in apparently the same uniform degree in every part of the earth. This proves not only that the earth is a curved body, but also that it is nearly of uniform curvature, or a sphere.

6th. Another proof of the rotundity of the earth is derived from the many voyages which have been performed around it. Magellan and his successors, pursuing constantly a western or eastern course, have at last returned to the place from whence they set out. It is evidently impossible that they could have so returned had the earth been a plane.

7th. Astronomers show that eclipses of the moon are occasioned by the earth intercepting for a while the moon's light from the sun. Now the portion of the moon's disk of which the light is intercepted has always a circular form: the earth, therefore, must be of a spherical figure, for a spherical body only can in every position project a circular shadow.

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 when compared with the immense magnitude of the earth are very inconsiderable. The height of the highest mountain does not exceed 29,000 feet, while the diameter of the globe, as we shall afterwards see, is more than 8,000 miles.

From the obvious appearances, therefore, which have been noticed, we are entitled to conclude that the form of the earth must be at least nearly spherical. This truth being established, we shall next consider the relation of the earth to the other great bodies of the universe. After this and some other subjects have been explained, we shall resume consideration of the figure of the earth, and inquire how far it deviates from an exact sphere.

Relation of the Earth to the System of the Universe.] It belongs to astronomy to explain the motions, magnitudes, and distances of the heavenly bodies, and the physicial laws by which the movements of these bodies are carried on; but it seems to be necessary in a work which treats of the science of geography, slightly, at least, to notice the place which the earth occupies in the great system of the universe. To this subject, therefore, and the mode in which the earth is illuminated by the sun, we shall now proceed.

The Visible Horizon.] If we place ourselves on the top of a tower, or in the midst of a large plain, the heavens will seem to be a vast hemisphere supported upon the earth. The circle in which the earth and heavens appear to meet, is termed the visible horizon.

Motion of the Stars.] If we attentively examine the motions of the stars, they will be found to rise at different points of the horizon, to move in plains parallel to each other, and to set at points more or less distant from those at which they arose. It will also be found that they constantly preserve the same relative distances in regard to each other: always rising and setting at the same points of the horizon, and moving in the same plains, so that the starry vault appears to turn tout d'une piece round the earth. A revolution of the stars is accomplished in rather less than twenty-four hours. The magnitude of the circles in which the stars appear to move, gradually dminishes as we advance towards the north, and at last dwindles to a point.

Cardinal Points.] It is necessary here to remark, that the north and south points are those in which the horizon is cut by a circle perpendicular to it, and passing through the point of the heavens which remains stationary, and the place of an observer. Another circle, perpendicular to the last, and also passing through the place of an observer, will indicate by its intersections with the horizon, the east and west.

Apparent Motions of the Sun.] On attending to the motions of the sun, it will be seen that that luminary, besides its apparent diurnal motion round the earth, along with the other heavenly bodies, daily changes its position in relation to the stars in a twofold manner. First, it does not, like them, always rise and set at the same points of the horizon; but, in a gradual manner, alternately advances to and recedes from the north. In the second place, it has a motion also towards the east, for the stars which on any particular day are seen setting immediately after it, will in a few days, appear rising before it, and their rising will daily more and more precede that of the sun. After the lapse of a year, having apparently made a complete circuit among the stars, the sun will seem to have returned to its former relative position. Astronomers, in order the better to estimate this apparent motion of the sun, referred it to the groups of fixed stars, termed constellations, through which the sun appears necessarily to pass. Zodiac and its Signs.] These constellations, which are twelve in number, are also denominated signs; and the zone of the heavens in