Chap. VIII. ANTIENT METAPHYSICS. 441 



likewife been carried on differently, there might have been fome dif- 

 ficulty in the matter. But, I think, I have fhown very clearly, that 

 they are both carried on by the fame Power, namely Pvlind. — There 

 may have been another reafon, as I have obferved, why Sir Ifaac 

 fuppofed their Motion to be begun by Impulfe, namely, that this 

 Motion is, by the neceffity of its Nature, always in Straight Lines ; 

 and, without analyfmg the Planetary Motion into Straight Lines, it 

 was impoffible, as I have faid, to demonftrate its Laws. And there 

 may have been likewife another reafon, viz. that, in Motion begun 

 by Bodily Impulfe, the Moving Power is perceptible by the fenfe ^ 

 whereas that Moving Power I call Mind falls under the perception 

 -of no fenfe, and, therefore, is not fo obvious. 



Another error, that this comparifon has led the Newtonians into, 

 is to fuppofe that the Planetary Motion is compounded, as theyfup- 

 pofe the Motion of Projedliles to be. And, indeed, if the Pro- 

 je£lile Motion w^ere not only begun by Bodily Impulfe, but car- 

 ried on, either by Bodily Impulfe, or by Mind defledting it into 

 a Curve, it muft neceffarily be compounded, according to the defini- 

 tion of compounded Motion above given. * But, as I think I have 

 fhown that it muft necefl'arily be carried on by Mind, and by Mind 

 only, as well as the Planetary Motion, it follows that, by the fame 

 neceffity, the Motion in both muft be fimple. 



3//0, As the Projedile, when it is not moved by Impulfe in the 

 Parabola, has a defcent, or tendency to defcend, in a Straight Line 

 towards the Centre ; fo, they fuppofed that the Planet, if it was not 

 projected (to fpeak in their language), would fall down to the 

 Centre, but without the leaft proof, or probability, as I think I have 

 •fhown J. 



Vol. n. K k k Thus 



* See P. 389. t Sec P. 400. 



