ANGLES. 21 



perfectly arbitrary. The circle might have been divided into just 

 100, or 1000 parts, and these called degrees, but it was convenient 

 to adopt for the length of a degree, a space which would represent 

 the progress of the sun in one day as nearly as was possible. 

 When we speak of a degree, it must be remembered that an 

 absolute length is not meant, but only the 1-360 part of some 

 circle. The length which belongs to a degree will vary with every 

 different circle. Thus in this diagram, we have two circles with 



a common centre, and two lines drawn from that centre, including 

 20 degrees of each circle. 



All circles are supposed therefore, to be divided into 360 parts, 

 and the 1-360 part of any circle is called a degree. Two kinds 

 of circles are supposed to be traced on the earth, as also in the 

 heavens, viz, great and small circles; this name does not arise 

 from the fact that one circle is actually greater than another, the 

 distinction is more marked, and is this 



Let A B C D, &c,, represent the earth, and let GC be a circle 



