268 A N T I E N T METAPHYSICS. Book II. 



fame kind were not governed by tlic fame general laws, but with 

 fuch difference, as the different raaffes of the bodies, and their differ- 

 ent diflances from the center, ought to produce. For I hold it to be a 

 general law of Nature, that things related do mutually affed one ano- 

 ther, and different relations of things produce different efftds ; for, 

 .otherwifc, the relation would be to no purpofe, contrary to that 

 axiom, as it may be called, of natural philofophy, * Thar Nature has 

 * done nothing in vain.' Now, there is certainly a relation betwixt 

 the body that is moved round, and the body round which it is mo- 

 ved ; and, as all relations are mutual, thefe two bodies, therefore, 

 muft mutually affe<51: one another ; and it would be anomalous in Na- 

 ture, and out of rule and order, if the different proportions of maffes, 

 and of diftances, betwixt the bodies furrounded andfurrounding, made 

 no difference as to the motion of the furrounding bodies. AH thefe 

 differences Sir Ifaac has combined, and eftimated the effects of them, 

 with wonderful fagacity, and has fhown a power of inveftigation and 

 dedudion, which does honour to the human genius, proceeding from 

 what is compounded to what is fimple, from effeds to caufes, and from 

 particular caufes to caufes more general ; from the motions of bodies, 

 inferring the moving forces ; and, from the analyfis of the motion of 

 projectiles here on earth and of the celeftial bodies, and the comparl- 

 fon of thofe two motions thus analyzed, raihng general theorems of 

 motion ; and, lajlly^ from thofe theorems reafoning downwards, and, 

 in that way, accounting for many phaenomena of nature, of which no 

 account had been given before, and which were therefore judged to 

 be irregularities and enormities in the fyliem. 1 fhould ftill admire 

 Sir Ifaac more, if I had gone deeper into mathematics ; but, having 

 only learned, as I have faid, the elements of geometry, the principles 

 of the fcience, and the manner of reafoning ufed in it, 1 cannot pre- 

 tend to follow Sir Ifaac in his demonftraiions and calculations ; which, 

 therefore, 1 muft content myfelf with believing only, to be pertedly 

 juft and accurate j and, if I could iufped any miiUke in Sir Ifaac's 



calcu- 



