168 HISTORY OF PHYSICAL ASTRONOMY. 



every minute through a space of thirteen feet. But 

 by noticing the space which bodies would fall in 

 one minute at the earth's surface, and supposing 

 this to be diminished in the ratio of the inverse 

 square, it appeared that gravity would, at the 

 moon's orbit, draw a body through more than fifteen 

 feet. The difference seems small, the approximation 

 encouraging, the theory plausible; a man in love 

 with his own fancies would readily have discovered 

 or invented some probable cause of this difference. 

 But Newton acquiesced in it as a disproof of his 

 conjecture, and '" laid aside at that time any further 

 thoughts of this matter ;" thus resigning a favourite 

 hypothesis, with a candour and openness to con- 

 viction not inferior to Kepler, though his notion 

 had been taken up on far stronger and sounder 

 grounds than Kepler dealt in ; and without even, so 

 far as we know, Kepler's regrets and struggles. Nor 

 was this levity or indifference; the idea, though 

 thus laid aside, was not finally condemned and 

 abandoned. When Hooke, in 1679, contradicted 

 Newton on the subject of the curve described by a 

 falling body, and asserted it to be an ellipse, Newton 

 was led to investigate the subject, and was then 

 again conducted, by another road, to the same law 

 of the inverse square of the distance. This naturally 

 turned his thoughts to his former speculations. Was 

 there really no way of explaining the discrepancy 

 which this law gave, when he attempted to reduce 

 the moon's motion to the action of gravity ? A sci- 





