Chap. VI. ANTIENT METAPHYSICS. 427 



I will conclude this Chapter with obferving, that the example 

 above mentioned, of the Compofition of Motion, is fufFicicnt of 

 itfclf, I think, to refute an argument much infilled on by the New- 

 tonians, that the fame EfFe<ft muft be produced by the fame Caufe ; 

 and that, therefore, as the Motion of the Projedile is of the fame 

 kind with the Motion of the Planet, it muft be produced by the 

 fame Caufe, that is, by Bodily Impulfe, and, likewife, by two 

 Moving Powers, as they fuppofe the Motion of ProjeiStiles to be. 

 But, in the example above given, we may fuppofe the Motion in 

 the Diagonal of a Parallelogram to be produced, either by the Im- 

 pulfe of a fingle Body, or by the Impulfe of two Bodies; or, laftly, 

 by Mind without any Body at all. Thefe Caufes of tlie Move- 

 ment are very different, and yet the EfFedt, that is, the Motion, 

 will be the fame, and will be governed by the fame Law. 



And here we may obferve, how neceffary it is to dlftinguifli 

 betwixt the Motion and the Caufe of the Motion : In the in- 

 ftance I have given, the Motion, by which ever of the three 

 Caufes it is produced, will be the fame, and governed by tlie 

 fame Laws. And in like manner the Planetary Motion, whether 

 produced by Mind or Body, by Gravitation and Projedion, 

 a.(£lually or only hypothetically, will be the fame Motion, and 

 governed by the lame Laws. And therefore the Mathematician 

 who defires to demonftrate what thofe Laws are, may chufe any 

 of the HypoChefes that fuits his purpofe beft ; nor is he at all 

 concerned to fhew that the Motion is adually fo produced, but 

 only that it may be fo produced. 



Hhha CHAP. 



