220 



A Short History of Astronomy 



[CH IX. 



he refers to the calculation as not having been made accu- 

 rately enough. It is probable that he used a seriously 

 inaccurate value of the size of the earth, having overlooked 

 the measurements of Snell and Norwood (chapter VIIL, 

 159) ; it is known that even at a later stage he was unable 



FIG. 71. The moon as a projectile. 



to deal satisfactorily with the difficulty above mentioned, 

 as to whether the earth might for the purposes of the 

 problem be identified with its centre ; and he was of course 

 aware that the moon's path differed considerably from a 

 circle. The view, said to have been derived from Newton's 

 conversation many years afterwards, that he was so dis- 

 satisfied with his results as to regard his hypothesis as 



