LAW OF GRAVITATION. 215 



and the discovery of the single law by which these 

 forces are every where regulated, was the great 

 discovery of Newton : and we wish to make it 

 appear that this law is established by an intelli- 

 gent and comprehensive selection. 



The law of the sun's attraction upon the planets 

 is, that this attraction varies inversely as the 

 square of the distance; that is, it decreases as 

 that square increases. If we take three points 

 or planets of the solar system, the distances of 

 which from the sun are in the proportion, 1, 2, 

 3 ; the attractive force which th sun at these 

 distances exercises, is as 1, l-4th, and l-9th 

 respectively. In the smaller variations of dis- 

 tance which occur in the elliptical motion of 

 one planet, the variations of the force follow the 

 same law. Moreover, not only does the sun 

 attract the planets, but they attract each other 

 according to the same law ; the tendency to the 

 earth which makes bodies heavy, is one of the 

 effects of this law : and all these effects of the 

 attractions of large masses may be traced to the 

 attractions of the particles of which they are 

 composed; so that the final generalization, in- 

 cluding all the derivative laws, is, that every 

 particle of matter in the universe attracts every 

 other, according to the law of the inverse square 

 of the distance. 



Such is the law of universal gravitation. Now, 

 the question is, why do either the attractions of 



