2 GEOGRAPHY. 



parallel to the equator are parallel circles, or parallels of latitude. Great 

 circles passing through both poles are called Meridians. The geographical 

 latitude of a place is its angular distance from the equator, measured along 

 a meridian ; it will be north or south as the place is north or south of the 

 equator. The geographical longitude of a place is that arc of the equator 

 intercepted between two meridians, one passing through the place and the 

 other through the arbitrary point to which the longitude is referred. This 

 latter meridian is called the first or fixed meridian, and differs in different 

 countries. The French take as their first meridian the one passing through 

 the observatory at Paris ; the Germans make use of the meridian of Ferro, 

 20° west of that at Paris, and passing near the island of Ferro. The 

 English make all references to the meridian of Greenwich, 1T° 46' east of 

 that of Ferro, as do the Americans also. In this country, however, an 

 effort has recently been made to have a meridian of our own, passing 

 through the city of New Orleans, as most convenient on account of its being 

 as nearly as possible 90° west of Greenwich. Our maps are drawn w^ith 

 reference to the meridian of Ferro, but for greater convenience we shall 

 ns9 the meridian of Greenwich in the body of the work. Longitude may 

 be reckoned either west and east to the amount of 180° each, or entirely 

 west to 360°. The two circles of latitude at distances of 23 p on each side 

 of the equator, arc called the Tropics (the northern is the Tropic of Cancer, 

 the southern the Tropic of Capricorn) : the Polar or Arctic circles are those 

 circles of latitude 23^° from each pole, the northern parallel being the 

 Arctic, the southern the Anatarctie circle. Tliese four circles divide the 

 earth into five zones : one torrid, two temperate, and two frigid. The torrid 

 scone is bounded by the two tropics, and embraces all that part of the earth 

 wht^re the rays of the sun fail vertically once or twice a year. The north 

 frigid xone lies within the Arctic circle, the south frigid zone Avithin the 

 Antaretic : both together include that portion of the earth where the sun, 

 (luring tlie summer, does not fall 'below the horizon for from twenty-four hours 

 to six months^ and during winter does ijot pass above the horizon for the same 

 limits of time. Each of the temperate zones lies between the tropic and polar 

 circles of its hemisphere. The two temperate zones together include more 

 than half yVo o^ tlie entire surface of the earth, the torj-id embracing jW, and 

 the two frigid only yfo- 



The equator, like any other circle, is divided into 360°. the sixteenth part 

 of a degree, or one minute, being called a geographical mile. The entire 

 circumference of the -earth at the equator will therefore be 21,600 

 geographical miles, the diameter being 6875J. Were the earth a perfect 

 sphere, then, her surface would amount to about 148,512,000 square miles, 

 and her volume to 170,176 millions of cubic miles. Measurements, 

 however, carried on at various times, and in various places, within the last 

 one hundred years, have shown that degrees of the meridian ,are not of the 

 same length at all latitudes, but that they increase slightly from the equator 

 towards the poles; it has hence been concluded that the earth in all 

 strictness is not a sphere, but an elliptical spheroid, flattened or depressed 

 at the poleSj or in other words, is such a body avS would be produced by the 

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