Chap. L A P P r: N D I X;- 29Q 



adion of t^vo Bodies, one of them projcdino; the Planet in a ftraiVht 

 line, which gave It the Progrcflivc Motion, and the. other impelli'ng 

 it towards the centre ; for, I think;, it is very clear, that Sir Ifaac had 

 then no diftindt Idea of Motion by Mind, nor, indeed, of the nature 

 of Mind as diftind: from Body, otherwife I think it is impofTible that 

 he would have endeavoured to account for gravltat'icn by the a£lion 

 of aether or air, or fome mediun^, cor/)ore n I or' incorporeal, inipeiWn^ 

 the Bodies floating in it tovv\ards one another *. Even wlien lie 

 wrote his letter to Dr Eentley, which was feveral vears after the 

 publication of his Principia, he had no fixed opinion, whether 

 gravitation wasproducd by a material or an Immaterial agent f; And 

 it appears that it was not till he wrote the Queries fubjolned to the 

 fecond edition of his Optics, when he firfl: began to philofophife con- 

 cerning the origin and continuation of Motion, that he determined the 

 matter in favour of Mind,; though even there he does not name 

 Mind, but only fpeaks g^ certain active Principles, which, I think 

 muft be Mind, as there is nothinfr elfe adtive in Nature 1. Accordino- 

 therefore, to Sir Ifaac's notion w^hen he wrote his Principla, the com- 

 pofitionof the Motion is produced, nnT:, by the Projedlon of the 

 Planet, and the vis injita, w^hich carries it' on in confequence of the 

 Projedlon, and, fecondly, by the CentripetarFoi'<Jei:-And in this vl^ay, 

 I think, I have fhown, that Sir Ifaac's fyftem is more confident v,?ith 

 itfeif than ^ny that has be^n fnice devifed §. 



The next method of this compofition I fhall take notice of, Is 

 that which, I believe, mod generally prevails ambngfl: the Newto-*' 

 lians at prefent, viz. That the Progreffive Motion is produced by ' 



Body 



* See Vol. ii. p. 324. where I have quoted the paillige at large. 



t See Vol. ii. p. ^76. , . . 



' \ Ibitl. p. 358. Sec alfo the ahove quotation from p. 37(5.'"wliere I lirfve given a 

 haftory of the progrefs of Sir Ifaac's opinions as to the origin and continuatioii of Mt)-^1 

 tion. iiiWl >ii jna 



^ P.:ige 289. of this Volume, and Vol, ii. p. 331. 



