/ The Earth considered as a Planet. 71 



others. The nearer we approach to them, 

 the more we find the earth becomes bar- 

 ren and inhospitable ; so that, under the 

 poles, the cold is so excessive, that the 

 country must be nearly uninhabitable. 

 Imagine now a circle to be drawn round 

 the globe, exactly in the middle, between 

 these two points, and this will be the 

 Equator ; which, properly speaking, is a 

 great circle of the earth, that separates 

 the northern from the southern hemis- 

 phere, and is every where at an equal dis- 

 tance from the poles. This circle is al- 

 so no less remarkable, on account of its 

 situation, than the poles ; the heat being 

 here almost as intense as the cold is 

 there. Every place is said to have north 

 or south latitude as it is on the northern 

 or southern side of this great circle. 



The Tropics are lesser circles parallel 

 to the equator, and each of them is 23 1 

 degrees from it ; a degree in this sense 

 being the 360th part of any great circle 

 which divides the earth into two equal 

 parts. The northern tropic touches the 

 ecliptic at the beginning of Cancer, and 

 is thence called the Tropic of Cancer ; 

 the southern tropic, touching the ecliptic 



