,ner.iv.J DISSERTATION SECOND. 95 



every particle of matter had a tendency to unite with every 

 other ? Or was that tendency directed only to particular 

 centres ? It could hardly be doubted that the tendency was 

 common to all the particles of matter. The centres of the 

 great bodies had no properties as mathematical points, they 

 had none but what they derived from the material particles 

 distributed around them. But the question admitted of 

 being brought to a better test than that of such general rea- 

 soning as the preceding. The bodies between which this 

 tendency had been observed to take place, were all round 

 bodies, and either spherical or nearly so, but whether great 

 or small, they seemed to gravitate toward one another ac- 

 cording to the same law. The planets gravitated to the 

 sun, the moon to the earth, the satellites of Jupiter toward 

 Jupiter ; and gravity, in all these instances, varied inversely 

 as the squares of the distances. Were the bodies ever so 

 ■mall — were they mere particles — provided only they were 

 round, it was therefore safe to infer, that they would tend 

 to unite with forces inversely as the squares of the distances. 

 It was probable, then, that gravity was the mutual tendency 

 of all the particles of matter toward one another ; but this 

 could not be concluded with certainty, till it was found, 

 wheilier great spherical bodies composed of particles gravi- 

 tating according to this law, would themselves gravitate ac- 

 cording to the same. Perhaps no man of that age but 

 Newton himself was fit to undertake the solution of this 

 problem. His analysis, either in the form of fluxions or in 

 that of prime and ultimate ratios, was able to reduce it to the 

 quadrature of curves, and he then found, no doubt infinitely 

 to his satisfaction, that the law was the same for the sphere 

 as for the particles which compose it ; that the gravitation 

 was directed to the centre . of the sphere, and was as the 

 quantity of matter contained in it, divided by the square 

 of the distance from its centre. Thu§ a complete expres- 



