INDUCTIVE EPOCH OF NEWTON. 161 



masses of the sun, earth, and planets, arises from 

 the attraction of each particle of these masses; 

 which attraction follows the above law, and belongs 

 to all matter alike. 



The history of the establishment of these five 

 truths will be given in order. 



1. Sun's Force on Different Planets. With re- 

 gard to the first of the above five propositions, that 

 the different planets are attracted to the sun by a 

 force which is inversely as the square of the dis- 

 tance, Newton had so far been anticipated, that 

 several persons had discovered it to be true, or 

 nearly true ; that is, they had discovered that if the 

 orbits of the planets were circles, the proportions of 

 the central force to the inverse square of the dis- 

 tance would follow from Kepler's third law, of the 

 sesquiplicate proportion of the periodic times. As 

 we have seen, Huyghens' theorems would have 

 proved this, if they had been so applied; Wren 

 knew it; Hooke not only knew it, but claimed a 

 prior knowledge to Newton ; and Halley had satis- 

 fied himself that it was at least nearly true, before 

 he visited Newton. Hooke was reported to Newton 

 at Cambridge, as having applied to the Royal So- 

 ciety to do him justice with regard to his claims; 

 but when Halley wrote and informed Newton (in a 

 letter dated June 29, 1686), that Hooke's conduct 

 "had been represented in worse colours than it 

 ought," Newton inserted in his book a notice of these 

 his predecessors, in order, as he said, "to compose 

 VOL. H. .M 



