« הקודםהמשך »
Of the E A R T H.
to give a more particular account of the planet which we inhabit.
The Earth, though called a globe, is not perfeótly round, but is widened at the equator, and flattened at the poles; so that its diameter from east to west, is about thirty miles longer than from north to south. Its figure is an oblate spheroid. It moves round the sun once in a year. This is called the earth’s annual motion, to which we are indebted for the difference in the length of the days and nights, and for the variety in the seasons. The diameter of the earth’s orbit, is 19C,346,ooo miles. And since the circumference of a circle, is to its diameter, as 355 is to 1 13, the circumference of the earth's orbit is 597,987,646 miles. And as the earth deB 2 scribes
- N artificial globe is a round body, whose surface is every where
Circles.] A circle passing through the centre of a globe, and thereby dividing it into two equal parts or hemispheres, is called a great circle. Of these there are fix.-The equator, the meridian, the ecliptic, the horizon, and two colures.
Circles dividing the sphere into unequal parts, are called small or loser circles, of which there are four, the two tropics, and the two polar circles.
Equator.] The equator is that line or circle which encompasses the middle of the earth, dividing the northern half from the southern. This line is often called the equinoëtial, because, when the sun appears therein, the days and nights are equal in all parts of the world.—From this line latitude is reckoned.
Latin names of English names. Charac- Months in which the
the figns. ters. sun enters them. I Aries The Ram cy. March 2 Taurus The Bull 8 April 3 Gemini The Twins LI May 4 Cancer The Crab gó June 5 Leo The Lion Sl July 6 Virgo The Virgin mg August 7 Libra The Scales o: September 8 Scorpio The Scorpion m. Oćtober 9 Sagittarius The Archer f November 1o Capricornus The Goat Vof December 11 Aquarius The Water-Bearer : January 12 Pisces The Fishes × February
Zodiac.] If two circles were drawn parallel to the ecliptic, at the distance of eight degrees on each fide of it, the space, or girdle included between these two parallels, fixteen degrees broad, and divided in the middle by the ecliptic, will comprehend within it the orbits of all the planets, and is called the Zodiac. Horizon.] The horizon is represented on the artificial globe by a broad wooden circle, dividing it into upper and lower hemispheres. There are, geographically speaking, two horizons, the sensible and the rational. The sensible horizon is that circle which limits our prospect; where the sky and the land and water appear to meet. The rational or real horizon, is a circle whose plane passes through the centre of the earth, dividing it into upper and lower hemispheres. The horizon is divided into four quarters, and each quarter into 9o degrees. The four quartering points, viz. east, west, north, and south, are called the Cardinal points. The poles of the horizon are the zenith and the nadir. The former is the point directly over our heads; the latter the point directly under our feet. Colures.] The colures are two meridian lines which divide the globe into four quarters. They are called colures, to distinguish them from other meridians. They both pass through the poles of the world, and one of them through the equinoëtial points Aries and Libra; the other through the solstitial points Capricorn and Cancer: The former is called the equino&tial, the latter the solstitial colure. Tropics.] The tropics are two circles drawn parallel to the equator, at the distance of 23° 30' on each fide of it. These circles form the limits, of the ecliptic, or the sun’s declination from the equator. That which is in the northern hemisphere, is called the tropic of Cancer; because it touches the ecliptic in the fign Cancer ; and that in the southern hemisphere, is called the tropic of Capricorn, because it touches the ecliptic in the sign Capricorn. On the 21st of June the sun is in Cancer, and we have the longest day. On the 21st of December the sun is in Capricorn, and we have the shortest day. They are called tropics, from the Greek word trepô, to turn, because when the sun arrives at them, he returns' again to the equator. * - Polar Circles.] The two polar circles are described round the poles of the earth, at the distance of 23° 30'. The northern is called the Arāic circle, from Arāos, or the bear, a constellation fituated near that place in the heavens; the southern, being opposite to the former, is called the Antarăic circle.—The polar circles bound the places where the sun sets daily. Beyond them the sun revolves without setting. Zones.] The tropics and polar circles divide the globe into five parts, called. Zones, or Belts; viz. One torrid, two temperate, and two frigid zones. The Torrid Zone, 47 degrees broad, is bounded by the tropics, and divided in the middle by the equator. It is called the torrid or burning zone, because the sun, being always over some part of it, makes it extremely hot. Each of the Temperate Zones is 43 degrees in breadth. The one which lies between the tropic of Cancer and the arétic circle, is called the north temperate zone; and the other, lying between the tropic of Capricorn and the antarótic circle, is called the south temperate zone. The mildness of the weather in these spaces, which are between the extremes of heat and cold, has acquired to them the name of temperate zones. : The two Frigid Zones, so called on account of the extreme cold of those regions, are included between the polar circles and the poles. Each of them is 23° 30' broad. Climates.] By a number of other circles, drawn parallel to the equator, the earth is divided into climates. - A Climate is a tract of the earth’s surface, included between the equator. and a parallel of latitude, or between two parallels of such a breadth, as that the length of the day in the one, be half an hour longer than in the other. Within the polar circles, however, the breadth of a circle is such, that the length of a day, or the time of the sun's continuance above the horizon without setting, is a month longer in one parallel, as you proceed northerly, than in the other. Under the equator, the day is always twelve hours long. The days gradually increase in length as you advance either north or south from