8 HISTORY OF 



performs in twenty-four hours. Thus, like a cha- 

 riot wheel, it has a compound motion j for while 

 it goes forward on its journey, it is all the while 

 turning upon itself. From the first of these two 

 arise the grateful vicissitude of the seasons ; from 

 the second, that of day and night. 



It may be also readily conceived, that a body 

 thus wheeling in circles, will most probably be 

 itself a sphere. The earth, beyond all possibility 

 of doubt, is found to be so. Whenever its sha- 

 dow happens to fall upon the moon, in an eclipse, 

 it appears to be always circular, in whatever posi- 

 tion it is projected : and it is easy to prove, that 

 a body which in every position makes a circular 

 shadow, must itself be round. The rotundity of 

 the earth may be also proved from the meeting 

 of two ships at sea : the top-masts of each are the 

 first parts that are discovered by both, the under 

 parts being hidden by the convexity of the globe 

 which rises between them. The ships, in this 

 instance, may be resembled to two men who ap- 

 proach each other on the opposite sides of a hill ; 

 their heads will first be seen, and gradually, as 

 they come nearer, they will come entirely into 

 view. 



However, though the earth's figure is said to 

 be spherical, we ought only to conceive it as be- 

 ing nearly so. It has been found, in the last age, 

 to be rather flatted at both poles, so that its form 

 is commonly resembled to that of a turnip. The 

 cause of this swelling of the equator is ascribed 

 to the greater rapidity of the motion with which 

 the parts of the earth are there carried round ; 



