Astronomy. [Lecture 18. 



orbit, when he is at A he will appear to a 

 spectator at S to be at E among the fixed stars, 

 when at B he will appear at F, when at C at 

 H, &c. 



Now let us reverse the supposition, and con- 

 sider the place of the sun as it really is at S, 

 and let us regard ABCD as the earth's orbit, 

 and we shall find the result substantially the 

 same as to the appearance of the sun in the 

 heavens. That is, when the earth is at A, the 

 sun will appear among the stars at H; when 

 at B, the sun will appear at G; when at C, 

 the sun will be at E. Though the sun there- 

 fore does not in reality change his place, you 

 must perceive that to a spectator on the earth 

 he will in fact appear to describe the same circle 

 EFGH in the starry heavens, as if he had been 

 the moving body instead of our earth. v 



The earth's orbit being an ellipsis, the sun 

 is not always at equal distances from it. When 

 in his apogtj, the sun is about 1171468 leagues 

 further from us than when in his perige\ In 

 this last case then not only must he subtend a 

 greater angle, butj it would appear that we 

 should derive from him a greater degree of 

 heat. The difference of temperature between 

 summer and winter does not, however, depend 

 solely on our proximity to the sun or our 

 distance from him, though this Cause is not 

 without its influence ; for in truth the sun is in 

 his apoge in our summer, and in his perige in 



