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23d of September, the circle described by the sun was at an equal distance from both of the poles. This circle, therefore
, muft divide the earth into two equal parts, and on this account was called the Equator or Equaller. It was also called the Equinoctial Line, because the sun, when moving in it, makes the days and nights of equal length all over the world. Having also observed, that, from the 21st of June to the ad of December, the fun advanced every day fowards a certain point, and having arrived there, returned towards that from which he had set out, from the 22d of December to the 2ift of Junethey fixed these points, which they called Soytices, because the direct motion of the sun was stopped at them; and represented the bounds of the sun's motion by two circles, which they named Tropics, because the sun no sooner arrived there than he turned back. Astronomers, observe ing the motion of the sun, found its quantity, at a ntean rate, to be nearly a degree (or the 360th part) of a great circle in the heavens, every twenty-four hours. This great circle is called the. Ecliptic, and it passes through certain constellations, distinguished by the names of animals, in a zone called the Zodiac. It touches the tropic of Cancer on one side, and that of Capricorn on the other, and cuts the equator obliquely, at an angle of twenty-three degrees twenty-nine minutes, the sun's greatest declination. To express this motion, they supposed two points in the heavens, equally distant from and parallel to this circle, which they called the Poles of the zodiac, which, turning with the heavens, by means of their axis, describe the two polar circles. In the artificial sphere, the equinoctial, the two tropics, and two polar circles, are cut at right angles by two other circles called Colures, which serve to mark the points of the solstices, equinoxes, and poles of the zodiac. The ancients also observed that when the sun was in any point of his course, all the people inhabit. ing directly north and fouth, as far as the poles, have noon at the same time. This gave occafion to imagine a circle passing through the poles of the world, which they called a Meridian, and which is immoveable in the artificial sphere, as well as the horizon, which is another circle representing the bounds betwixt the two hemispheres, or half spheres, viz. that which is above, and that which is below it,
By the Globe is meant the representation of the different places and
countries on the face of the earth, upon an artificial globe or ball. Geographers have represented the situation of one place upon this earth with regard to another, or with regard to the earth in general, by transferring the circles of the sphere to the artificial globe: and this is the only me thod they could employ. This will be abundantly obvious from an example. After that circle in the heavens, which is called the equator, was known to astronomers, there was nothing more easy than to transfer it to the earth, by which the situation of places was determined, according as they lay on one side of the equator or the other. The same may be observed of the other circles of the sphere above mentioned. The reader having obtained an idea of the principle upon which the
itself, or, in other words, the description of our earth, as represented by the artificial globe.
FIGURE OF THE EARTH] Though, in speaking of the earth with the other planets, it was sufficient to consider it as a Ipherical or globulas body,--yet it has been discovered that this is not its true figure, and that the earth, though nearly a sphere or ball, is not perfe&ly so. This occafioned great disputes between the philosophers of the last age, among whom fir Isaac Newton and Cassini, a French astronomer, were the heads of two different parties. Sir Isaac demonstrated from mathematical principles, that the earth was an oblate Spheroid, or that it was flatted at the poles, and jutted out towards the equator, so that a line, drawn through the centre of the earth, and passing through the poles, which is called a diameter, would not be so long as a line drawn through the fame centre and pasting through the cast and west points. The French philosopher asserted precisely the reverse; that is, that its diameter was lengthened towards the poles. In order to decide this question, the king of France, in 1736, fent out some able mathematicians towards the north pole, and likewile others towards the equator, in order to measure a degree, or the three hundred and sixtieth part of a great circle, in those different parts; and from their report, the opinion of fir Isaac Newton was confirmed beyond dispute. Since that time, therefore, the earth has always been considered as more flat towards the poles than towards the equator. The reason of this figure may be easily understood, if the reader fully comprehends what we formerly observed, with regard to the earth's motion. For if we fix a ball of soft clay on a spindle, and whirl it round, we shall find that it will jut ,out or project towards the middle, and flatten towards the poles. This is exactly the case with reSpect to our earth; only that its -axis represented by the spindle, is imaginary. But though the earth be not properly spherical, ibe difference from that figure is so small, that it may be represented by a globe, without any sensible error.
CIRCUMFERENCE AND DIAMETER OF THE EARTH.] In the general table which we have exhibited, page 4, the diameter of the globe is given according to the best observations ; fo that its circumference is 25,038 English miles. This circumference is conceived, for the conveniency of measuring, to be divided into three hundred and fixty parts or degrees, each degree containing sixty geographical miles, or fixty-nine English miles and a half. These degrees are in the fame manner conceived to be divided each into fixty minutes.
AXIS AND POLES OF THE EARTH.] The axis of the earth is that imaginary line paffing through its centre, on which it is supposed to turn round once in twenty-four hours. The extreme points of this line are called the Poles of the earth ; one in the north and the other in the south, which are exactly under the two points of the heavens called the North and South Poles. The knowledge of these poles is of great use to the geographer in determining the distance and fituation of places; for the poles mark, as it were, the ends of the earth, which is divided in the middle by the equator : so that the nearer one approaches to the poles, the farther he removes from the equator; and in removing from the poles, he approaches the equator.
CIRCLES of THE GLOBE.] There are commonly divided into the greater and leffer. A great circle is that whose plane passes through the centre of the earth, and divides it into two equal parts or hemispheres. A lefler circle is that which, being parallel to a greater, cannot pals
through the centre of the earth, nor divide it into equal parts. The greater circles are for in number, the lesser only four.
EQUATOR.] The first great circle is the Equator or Equinoctial; and by navigators called the Line. The poles of this circle are the same with those of the world. It passes through the east and west points of the world, and, as has been already mentioned, divides it into the northern and southern hemispheres. It is divided into three hundred and fixty degrees, the use of which will soon appear.
Horizox.] This great circle is represented by a broad circular piece of wood encompailing the globe, and dividing it into the upper and lower hemispheres. Geographers very properly distinguish the horizon into the sensible and rational. The first is that which bounds the utmost prospect
of our úght, when we view the heavens around us, apparently touching the earth or lea.
This circle determines the rising or setting of the sun and stars, in any particular place; for when they begin to appear above the eastern edge, we Tay they rile; and when they go beneath the western, we say they are set. It appears that each place has its own sensible horizon. The other horizon, called the rational, encompasses the globe exactly in the middle. Its poles (that is, two points in its axis, each ninety degrees distant from its plane, as those of all circles are) are called the Zenith and Nadir,-the former exactly above our heads, and the latter directly under feet. The broad wooden circle which represents it on the globe, has several circles drawn upon it: of these the innermoft is that exhibiting the number of degrees of the twelve signs of the zodiac (of which hereafter,) viz. thirty to each sign. Next to this, you have the names of these figns, together with the days of the month according to the old style, and then according to the new style. Besides these, there is a circle representing the thirtytwo thumbs, or points of the mariner's compass. The ule of all these will be explained hereafter.
MERIDIAN.) This circle is represented by the brass ring on which the globe bangs and turns. It is divided into three hundred and fixty degrees, and cuts the equator at right angles ; so that, counting from the equator each way to the poles of the world, it contains four times ninety degrees, and divides the earth into the eastern and western hemi. 1pheres. This circle is called the meridian, because, when the sun comes to the south part of it, it is then meridies or mid-day, and then the sun has its greatest altitude for that day, which is therefore called its meridian altitude. Now, as the sun is never in its meridian altitude at two places east or weft of one another at the same time, each of these places must have its own meridian. There are commonly marked on the globe twenty-four meridians, one through every fifteen degrees of the equator.
Zodiae.] The zodiac is a broad circle, which cuts the equator obliquely; in which the twelve figns above mentioned are represented. In the middle of this circle is supposed another
called the Ecliptic, from which
September 2. Taurus 8
April 8. Scorpio m October 3. Gemini I
9. Sagittarius # Noveinber 4. Cancer
June 10. Capricorn 1 December 5. Leo 2 July 11. Aquarius
COLURES.] If we imagine two great circles passing both through the poles of the world, and one of them through the equinoctial points Aries and Libra, and the other through the solstitial points Cancer and Capricorn, these are called the Colures,--the one the Equinoctial, the other the Solftitial Colure.-- These are all the great circles.
Tropics.] If we suppose two circles drawn parallel to the equinoctial, at twenty-three degrees thirty minutes distance from it, measured on the brazen meridian, the one towards the north, the other towards the south, these are called Tropics, from the Greek word. Toen, a turning, because the sun appears, when in them, to turn backwards from his former course. The one is called the Tropic of Cancer, the other of Capricorn, because they pass through the first points of these signs.
Polar CIRCLES.] If two other circles are supposed to be drawn at the like distance of twenty-three degrees thirty minutes, reckoned on the meridian from the polar points, these are called the Polar Circles. The northern is called the Arctic, because the north pole is near the constellation of the Bear, in Greek repxtos; the southern, the Antarctic, because opposite to the former. And these are the four lesjer circles. Besides these ten circles now described, which are always drawn on the globe, there are several others which are only supposed to be drawn on it.
These will be explained as they become necessary, left the reader should be disgusted with too many definitions at the same time, without seeing the purpose for which they serve. The principal design of all these circles being to exhibit the respective situation of places on the earth, we shall proceed to consider more particularly how that is effected by them. It was found easier to distinguish places by the quarters of the earth in which they lay, than by their distance from any one point. Thus, after it was discovered that the equator divided the earth into two parts, called the Northern and Southern hemispheres, it was easy to see that all places on the globe might be distinguished, according as they lay on the north or south side of the equator.
Zones.] After the four lesser circles we have mentioned came to be known, it was found that the earth, by means of them, might be divided into five portions, and consequently that the places on its surface might be distinguished according as they lay in one or other of these portions, which are called Zones, from the Greek word Swin, which signifies a girdle; being broad spaces, like swathes, girding the earth about.
The torrid zone is that portion of the earth between the tropics, and called by the ancients torrid, because they conceived, that, being continually exposed to the perpendicular or direct rays of the sun, it was rendered uninhabitable, and contained nothing but parched and sandy deserts. This notion, however, has long since been refuted. It is found that the long nights, great dews, regular rains and breezes which prevail almost throughout the torrid zone, render the earth' not only habitable, but so fruitful, that in many places they have two harvests in a year; all sorts of spices and drugs are almost folely produced there ; and it furnishes the most perfect metals, precious stones, and pearls. In Mort, the countries of Africa, Asia, and America, which lie under this zone, are in all respects the most fertile and luxuriant
earth. The two tenperate zones are comprised between the tropics and polar circles. They are called temperate, because, meeting the rays of the sun obliquely, they enjoy a moderate degree of heat.
The two frigid zoncs lie between the polar circles and the poles, or rather are inclosed within the polar circles. They are called the frigid or frozen, because most part of the year it is extremely cold there, and