io8 



A Short History of Astronomy 



[CH. IV. 



unchanged ; and thus Coppernicus was able to give the 

 accompanying diagram of the solar system (fig. 40), repre- 

 senting his view of its general arrangement (though not of 

 the right proportions of the different parts) and of the 

 various motions. 



82. The effect of the motion of the earth round the sun 

 on the length of the day and other seasonal effects is 



FIG. 41. Coppernican explanation of the seasons. From the 

 De Revolutionibus. 



discussed in some detail, and illustrated by diagram^ which 

 are here reproduced.* 



In fig. 41 A, B, c, D represent the centre of the earth in four 

 positions, occupied by it about December 23rd, March 2ist, 

 June 22nd, and September 22nd respectively (i.e. at the 



* Fig. 42 has been slightly altered, so as to make it agree with 

 % .41- 



