72 The Earth considered as a Planet. 



at the beginning of Capricorn, is therefore 

 called the Tropic of Capricorn. 



The Arctic Circle has the north pole for 

 its centre, and is just as far from the north 

 pole as the tropics are from the equator ; 

 and the Antarctic Circle (hid by the sup- 

 posed convexity of the figure) is just as 

 far from the south pole, every way round , 

 it. 



The circles 12. 1. 2. 3. 4. &c. are meri- 

 dians to all places they pass through ; and 

 we must suppose thousands more to be 

 drawn, because every place that is ever 

 so little to the east or west of any other 

 place, has a different meridian from 

 that other place. All the meridians meet 

 in the poles ; and whenever the sun's cen- 

 ter is passing over any meridian, in his 

 apparent motion round the earth, it is 

 mid-day or noon to all places on that me- 

 ridian. The longitude of a place is its 

 distance east or west from the first meri- 

 dian, reckoned in degrees, minutes, &c. 

 upon the equator. Supposing we call 

 London the first, it will cut the equator 

 in two opposite points at the distance of 

 one hundred and eighty degrees each 

 way ; and as the equator is the boundary 



