328 



PHYSIOGRAPHY. 



[chap. 



northern hemisphere and a southern hemisphere. It is 

 further supposed that each of these halves is banded round 

 by a number of circles, which run parallel to the equator, 

 but get smaller and smaller on approaching the poles. These 

 circles are called small circles, while the equator is called a 

 great circle. The centre of a great circle must be the centre 

 of the sphere on which the circle is drawn ; and, it is plain, 

 that if the earth were to be cut through at the equator by a 

 flat plane, this plane must pass through the earth's centre : 



Fig. lo). — Parallels of latuude. 



Fig. 105. — Lines of lo.Tgitude. 



but planes passing through any of the sm.all circles, parallel 

 to the equator, would not pass through this central point. 



The equator serves the place of the line OA in Fig. 103 ; 

 it is, in fact, a standard line from which distances may be 

 measured. Every circle is divided, for convenience of 

 calculation, into 360 equal parts, called degrees ; and it is 

 supposed that the circumference of the earth is divided in 

 this way. The distance of any place from the equator, 

 measured along a circle which passes through the poles, and 

 expressed in degrees, is called \ht latitude^ of that place. 

 ' Latitude, from Lat. latitudo, breadth. 



