INTRODUCTION. 



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a circle of 654 feet ; Juno, Ceres, Vesta, and Pallas, grains of sand, in orbits of from 1000 

 to 1200 feet. Jupiter, a moderate-sized orange in a circle nearly half a mile across ; Saturn, 

 a small orange, in a circle of four fifths of a mile ; and Uranus, a full-sized cherry or small 

 plum upon the circumference of a circle, more than a mile and a half in diameter." 



II. THE EARTH, ITS FIGURE, DIMENSIONS, &c. 



1. The Earth. The earth is a planet, of a globular shape, and forming very nearly a 

 perfect globe or sphere. Like the other planets it has two motions ; its rotation on its own 



axis, completed in about 23 hours and 56 minutei, caus- 

 es the apparent daily revolution of the sun and t eavens 

 round the earth, and thus produces the alternatio i of day 

 and night ; its niotion in its orbit, which carries it round 

 the sun in about 365 days and 6 hours, produces the al- 

 ternation of the seasons. That the earth is round, is 

 proved by several consideralions, such as the shape of 

 its shadow on the moon during an eclipse ; the fact that 

 it is constantly circumnavigated, so that a ship, by steer- 

 ing in a general direction, either eastward or westward, 

 arrives again at its point of departure, and also by ihe 

 appearances, exhibited by vessels at sea. At a short 

 distance the hull of the vessel is sunk below the liorizon ; a little further the lower sails dis- 

 appear, and then the topsails. 



2. t^.T?s, Polea. The axis 

 of the earth is an imaginary 

 line passing through its cen- 

 tre, and about which it re- 

 volves ; the extremities of 

 the axis are called the poles ; 



the north pole is called Jlrc- 

 lllnstrationof the sphericity of the Earth. ^-^ p^j^,^ j-.^^^ j,^ j^^j^^^ j^^ 



the dii-ection of the Great Bear (in Greek ^irctos) ; the south pole, the Antarctic. 



3. Equator., JMcridian. An imaginary great circle, passing round the earih from east to 

 west, and equally distant from both poles, is called the equator ; imaginary great circles drawn 

 round the earth from north to south, passing through the poles, and intersecting the equator at 

 right angles, are called meridians. 



4. Latitude and Longitude. The relative position of a place on the earth's surface is 

 determined by its distance north or south of the equator, and its distance east or west of any 

 given meridian, called the prime meridian; on English and American maps and globes the me- 

 ridian of Greenwich in England, is generally assumed as the prime meridian ; but American 

 geographers often adopt that of Washington, and other nations those of their respective capitals. 

 Distance from the equator is called laiitudc ; distance from the prime meridian is called 

 longitude. 



5. Degrees, (^t. The geographical measure of distance is a degree or SGOth part of a gicai 

 circle of the earth ; the degree is divided into 60 minutes and the minute into 60 seconds. 

 Cn-cles passing round the earth parallel to the equator at given distances from each oilier, 

 whether of one, five, or ten degrees, are called parallels of latitude, and serve to show at uhat 

 distance from the equator are the points throurji which thev pass. In the same way meridians 

 are drawn round the earth's surface from north to south at ihe same distances. 



6. Tropics. In spring and autumn, the sun appears to ir.ove round the earth over the equa- 

 torial regions ; but in svmiraer the sun appears to be 23| degrees r.crih, and in ^\il:^er the same 

 distance south of the equator. Circles passing round the earth at iliese points are called tropics. 

 That at the south of the equator being the tropic of Capricorn, and that at the north the tropic 

 of Cancer. 



7. Polar Circles. When the sun is in the trojiic of Cancer, he is not visilile round the 

 Antarctic pole for a distance of 23h degrees ; and on the contrary, when he is in the tropic of 



