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was necessary, in order to give the requisite certainty to his accounts, and is very short in what he relates from others. He was a philosopher, as well as a geographer. Good sense, perspicuity, accuracy, and solidity of judgment, are visible in every part of his works. The geography of Ptolemy is more extensive; it takes in a greater part of the earth, while it seems to be equally circumstantial every where; but this extent renders it liable to more errors. He had the merit of carrying into full execution and practice the invention of Hipparchus, for designating the situation of places on the earth by latitude and longitude, after it had lain dormant upward of 250 years; and thus he greatly advanced the state of the science.

The Roman empire had heen enlarged to its greatest extent, and all its provinces well known and surveyed, when Ptolemy, about 150 years after Christ, composed his system of geography. The principal materials used in composing this work were, the proportions of the gnomon to its shadow, taken by different astronomers at the times of the equinoxes and solstices; calculations founded upon the lengths of the longest days; the measures or computed distances of the principal roads contained in the Roman surveys and itineraries; and the various reports of travellers and navigators, who often determined the distances of places by hearsay and conjecture. All these were compared together, and digested into one uniform body or system; and were afterwards translated by him, as far as was necessary in adopting the plan of Hipparchus, into the new mathematical language of degrees and minutes of longitude and latitude.

The degree of accuracy in the latitudes and longitudes, given by Ptolemy, depended upon the veracity of the facts or suggestions communicated to him, from which they were afterward deduced. We must not therefore be surprised at the multitude of errors to be found there, when his original materials were so imperfect for executing so large a work, as the fixing of the longitudes and latitudes of all the places, coasts, bays, and rivers of the then known world. His system, with all its imperfections, continued in vogue till the beginning of the 17th century; and the capital errors of Ptolemy's work kept their place in all maps, by a sort of unquestioned prescription, down even to that time.

Little was done in geography from the days of Ptolemy to the restoration of learning in Europe; for the Arabian geographers copied and retailed all his principal errors. They observed indeed, under their Caliph Almanon, in the beginning of the ninth century, a degree of latitude on the plains of Shinar near Babylon, and found it equal to 561 Arabian miles, each of which is 4000 cubits, or 6000 feel; hence they determined the circumference of the earth.

The ancients were acquainted with but a small portion of the earth's surface. On the west, the Atlantic ocean and British isles limited their knowledge. The Fortunate islands, now called the Canaries, were the remotest known lands towards the south. Their notions with regard to the northern countries were very imperfect:

Though Scandinavia was known, yet that and some other countries on the same continent were considered as large islands. It is not easy to determine what place the ancients understood by Ultima Thule ; many take it for Iceland, but Procopius thinks it was a part of Scandinavia. Their knowledge of Sarmatia and Scythia was far from extending to the sea, which bounds Russia and Great Tartary on the north-east. Their discoveries went no farther than the Riphean mountains, which now divide Russia from Siberia. The western frontier of China seems to have bounded their knowledge on the east. Ptolemy indeed had a very imperfect notion of the southern parts of that extensive empire. How far the ancients extended their discoveries with regard to Africa cannot be certainly known. Some are of opinion, that they were acquainted with the whole coast, having sailed round the southern extremity, now called the Cape of Good Hope, and extended their voyages from the Red Sea to the Mediterranean. Ptolemy, however, supposed that Africa was not surrounded by the sea, but extended in its breadth eastwardly till it joined to India.

lo the fifteenth century the Portuguese, animated with the desire of finding a passage to the East-Indies, pushed their enquiries along the western coast of Africa, till they found the Cape of Good Hope, in 1486. In 1497, Vasquez de Gama doubled the Cape, and the next year made a voyage to India, and thus completed ihe discovery of that country by the east. The passage being thus opened, several European nations, desirous of sharing in the rich commerce of the east, sent their ships to the Indian Sea, where they discovered the Asiatic islands, and penetrated to the empire of Japan. The voyages of the Russians have completed our knowledge of the eastern parts of the continent of Asia.

The Portuguese had just crossed the equator, when ChristoPHER COLUMBUS, a native of Genoa, conceived the idea of tinding India by a western course. In 1492, he crossed the Atlantic ocean : but, instead of the Indies he discovered the new WORLD.

The improvements in geography at the time of the revival of learning in Europe, and since, have been very much owing to the great progress of astronomy. More correct methods and instruments for observing the latitude have been invented; and the discovery of Jupiter's satellites afford a much easier method of finding the longitude, than was formerly known. Solar and lunar eclipses, transits of Mercury and Venus over the sun's disc, and occultations of the fixed stars by the moon, also furnish means for determining longitudes. And since the lunar tables were improved by Professor Mayer, and time keepers by Mr. Harrison and others, this important object has been obtainable by measuring distances of the moon from the sun and from certuin fixed stars, und by keeping time. The voyages of different nations brought to our knowledge a vast number of countries utterly unknown before, The late voyages of Capt. Cook and other navigators, together with the travels of Messrs. Bruce, Park, Mackenzie, and many others, contributed greatly to the improvement of geography during the 18th century; so that now the geography of the utmost extremi.

ties of the earth is in a fair way of being much better known to the moderns, than that of the adjacent countries was to the ancients. This science, however, is yet very far from perfection; and our best maps ought to be considered only as unfinished works, which are to be altered and corrected by farther observations and discoveries.

ASTRONOMY, .

AS CONNECTED WITH THE SCIENCE OF GEOGRAPHY.

Astronomy is the science, which treats of the heavenly bodies. By it we learn the figure and dimensions of the earth, and the relative situation of places upon its surface. Hence the propriety of giving a short account of this science in an Introduction to Geography

EXPLANATION OF TERMS.

Angle. An angle is the space included between two lines, which meet each other.

Circle. A circle is a regular figure, bounded by a curve line, every part of which is equally distant from a point within it, called the centre. The circumference of a circle is the curve line, which bounds it. The radius of a circle is a straight line drawn from the centre to the circumference; and the diameter is a straight line drawn through the centre from one side of the circumference to the other. The circumference of every circle is supposed to be divided into 360 equal parts, called degrees ; each degree into 60 minutes ; each minute into 60 seconds. An arc of a circle is part of its circumference. All angles are measured by arcs of circles, or by the number of degrees they contain.

Sphere. A sphere is literally a ball, or globe. By the celestial sphere is meant, the apparently concave orb, which surrounds the earth, and in which the heavenly bodies appear to be situated at equal distances from the eye. In order to facilitate the knowledge of the places of these bodies in the sphere, several circles are supposed to be described on its surface, and are denominated circles of the sphere. The circles of the celestial sphere are supposed to have their centres coincident with the centre of the earth, and to mark correspondent circles on the earth's surface, where their planes cut it; so that the celestial and terrestial spheres or globes are considered as concentric, and as having concentric circles on their surfaces.

Great Circles. Great circles are those, whose planes pass through the centre of the sphere, and, of course, divide it into two equal parts. Of these there are four, the Equator, the Ecliptic, the Meridian, and the Horizon.

Small Circles. Those circles, whose planes divide the sphere unequally, are called small circles. Their planes do not pass through its centre. The two Tropics, and the two Polar Circles, are small circles.

Axis. The axis of the earth, or any heavenly body, is an imaginary straight line passing through the centre, around which it performs its diurnal.rotation.

Poles. The poles are the extremities of the axis.

Equator. The Equator is a great circle, whose plane divides the earth and the heavens into northern and southern hemispheres. The axis of the earth makes a right angle with its plane. It is often called the Equinoctial ; because, when the sun is directly over it, the days and nights are of equal lengths in all parts of the world.

Meridian. The Meridian is a great circle, whose plane divides the earth and the heavens into eastern and western hemispheres. There is an indefinite number of meridians ; for all places, that lie east or west of each other, have different meridians. They all pass through the poles of the earth, and cut the equator at right angles. The word meridian is derived from meridies, mid-day ; because, when the sun is on the meridian of any place, it is noon at that place. Geographers usually assume the meridian, which passes through the metropolis of their own country, as the first meridian. But as great inconvenience and confusion result from this practice, the first meridian, throughout the following work, will be that of the Royal Observatory at Greenwich, near London.

Ecliptic. The Ecliptic is a great circle whose plane makes an angle of 23° 28' with the plane the equator. Conside ed as a circle in the heavens, its circumference is the path, which the earth describes annually in its revolution round the sun. The points in which the ecliptic intersects the equator are called the equinoctial points ; because, when the sun is in either of those points, it shines on both poles, and the day is then equal to the night throughout the earth. The meridian, which passes through these points, is called the equinoctial colure. The two points in the ecliptic, which are 90 degrees distant from these, are called the solstitial points. The meridian passing through these points is called the solstitial colure, and is the only meridian which cuts the ecliptic at right angles. The sun passes through the equinoctial points on the 20th March, and the 23d of September. The former is called the vernal ; the latter, the autumnal equinox. The sun is in the solstitial points on the 21st of June, and the 21st of December. The former is Galled the summer; the latter the winter solstice.

The ecliptic is divided into 12 equal parts of 30 degrees each, called signs. These begin at the vernal intersection of the ecliptic with the equator, and are numbered from west to east. The names and characters of the signs, with the months in wbich the sin enters them, are as follows:

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The first six are called northern signs; and the last six southern.

Zodiac. The Zodiac is a broad belt in the heavens, 16 degrees wide; in the middle of which is the ecliptic. It comprehends the orbits of all the planets.

Horizon. The horizon is either sensible or real. The sensible horizon is the small circle which limits our prospect, where the sky and land or water seem to meet. The real horizon is a great circle, parallel to the former, which divides the earth into upper and lower hemispheres.

The point of the heavens directly over our heads is called the Zenith ; and the opposite point, or that directly under our feet, is called the Nadir. The straight line connecting these two, passes through the centre of the horizon and is called its axis. The zenith and nadir of any place, therefore, are the poles of its horizon.

Declination. The declination of a heavenly body is its distance north or south of the equator, measured on a meridian.

Tropics. The Tropics are two small circles, drawn parallel to the equator, at the distance of 23 28 on each side of it. The northern is called the tropic of Cancer; the southern, the tropic of Capricorn. The sun never passes these circles ; but, when it has arrived at either, it turns, and goes toward the other. They, of course, bound those places where the sun is vertical.

Polar Circles. The Polar circles are two small circles, parallel to the tropics, described round the poles at the distance of 23o 28'; that around the north pole is called the arctic circle ; that around the south pole, the antarctic circle.

A direct or right sphere is that, where both the poles are in the horizon, and the sun, moon and stars ascend directly above, and descend directly below the horizon. This position is peculiar to those places, which are under the equator.

An oblique sphere is that, where all the diurnal motions are oblique to the horizon. This is common to all parts of the earth, except those under the poles and the equator. In an oblique sphere, one of the poles is elevated above, and the other depressed below, the horizon.

A parallel sphere is that where the equator and all its parallels are parallel to the horizon. This position is peculiar to those parts which lie directly under the poles.

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