Chap. I. A N T I E N T M K T A P H Y S I C S. 323 



And, hijlly, if Sir Ifaac had believed, as Dr Clarke did, that the 

 Motion of the celeftial Bodies was carried on by X.\\t conftant agency 

 of Mind, and not by viitue of any original impulfe*, he never could 

 have thought either of a Vis Imprejfa, or of a Vis Infita, by which he 

 fuppofes the Motion to be continued after the Vis Imprejfa, orthe/w- 

 pulfcy has ceafed ; for both of thefe are entirely unneceflary, accor- 

 ding to Dr Clarke's Syftem and mine. Nor would he ever have 

 thought of the Eternity of Motion, which he has laid down in his 

 firfl: Axiom : For he would have known that, if the Motion be car- 

 ried on by Mind, it will laft as long as the Mind continues to a£l: 

 upon the Body ; and that will be as long as it pleafes the great Au- 

 thor of Nature, and is fuited to the Syftem of the Univerfe. 



I will therefore venture to affirm, that Sir Ifaac, while he 

 was writing his Principia, had no thought of Motion by Mind, 

 but only confidered Motion by Body : And, however extra- 

 ordinary and unaccountable this may feem, there are two rea- 

 fons that may be given for it. In the firft place, the Motion 

 produced by Bodily Impulfe is the mod obvious to Senfe ; and, 

 indeed, the only Motion of which we can, by our Senfes, per- 

 ceive the Caufe : Whereas the Caufe of the other Motion cannot 

 be perceived by any Senfe, and is only difcovered, as I have elfe- 

 where obferved, by Confcioufnefsf, with which Geometers and Me- 

 chanics have nothing to do. id/jr. The Mechanical Phyfics were 

 fo much in fafhion at the time Sir Ifaac wrote, and tlie Philo- 

 fophy of Mind and of Nature were confidered to be fo perfectly di- 

 ftindt, that, if Sir Ifaac had endeavoured to account for the Motions 

 of the Celeftial Bodies by Mind, no body would have liftened to 

 him. All, therefore, he could do, in the ftate he found Philofophy, 

 was to deliver the Heavens from the Vortices of Des Cartes ; but, in 

 place of them, he was obliged, by the opinions of the times and the 



S s 2 preju- 



• See Vol. I. p. 512, 

 t Page 47. 



