NEWTON S PRINCTPIA. 9 



satellites, considers the planets as having a tendency to 

 resile from the sun and the satellites from the planets, 

 but as being &quot;drawn towards and held by those central 

 bodies, and so compelled to follow them in continued 

 revolutions.&quot; He also most accurately compares the re 

 ceding (or centrifugal) force with the tendency of a stone 

 whirled in a sling to fly off at every instant of its motion. 

 Hooke, a man of unquestionable genius, and whose partial 

 anticipations of many great discoveries are truly remarkable, 

 about the same time with Borelli, asserted that the at 

 traction of the sun draws away the planets from moving 

 in straight lines, and that the force of the attraction varies 

 with the distance. He had, as early as 1666, read to the 

 Royal Society a paper explaining the curvilinear motion 

 of the planets by attraction. Halley, as well as others, had 

 even hit upon the inverse duplicate ratio, by supposing 

 that the influence from the sun was diffused in a circle, or 

 rather a sphere, and that therefore the areas proportioned 

 to that influence were as the squares of the radii, and 

 that consequently the intensities, being inversely as those 

 areas, were inversely as the squares of the radii or dis 

 tances. Finally, Hooke had foretold, that whoever set 

 himself to investigate the subject experimentally would 

 discover the true cause of all the heavenly motions. 



Such were the near approaches which had been made 

 to the law of Gravitation before its final and complete 

 discovery. But although in this gradual progress it re 

 sembles almost all the other great improvements in 

 science, in one material respect it differs from them all. 

 The theory was perfect which Newton delivered, and the 

 whole subject was at once thoroughly investigated. It was 

 not merely that the general principle hitherto anxiously 

 sought for, and of which others had caught many glimpses, 

 was now unfolded and established upon appropriate founda- 



