Chap. I. APPENDIX. 317 



to doubt whether or not the Motions we obfervc in Nature, and par- 

 ticularly gravitation, might not be produced by an immaterial caufe *: 

 And, laft of all, when he wrote his Queries to his Optics, he lavs it 

 down, that the vis inerijae will not account for the continuation any 

 more than the beginning of Motion f ; and that therefore there 

 muft be an adive principle in body, fuch as Ariilotle fuppofed, and 

 which is no other than what I call Mind^ and which Ariftotle calls 

 a kind of life in Body J. Thus, it is evident that Sir Ifaac gave up, at 

 laft, his Firft Law of Motion, founded entirely upon the 'uis iuer- 

 tiae of bodies, by v>^hich he fuppofed they continued in Motion af- 

 ter it was once begun. In like manner, I cannot doubt but that the 

 prefent Newtonians, if they will philofophife upon the nature of 

 Motion, and the difference betwixt Motion produced by Body and 

 that produced by Mind,' as Sir Ifaac appears to have done w^hen he 

 wrote his Queries, w^ill give up this 'vis inertiae and vis infita^ which 

 they appear to be fo fond of, and then they will get free of all thofe 

 difficulties and abfurdities with which they have perplexed their fyf- 

 tem ; and, particularly, they will be able to demonftrate all the laws 

 of the Planetary Motion, without the ftrange fuppofition of one and 

 the fame Motion being produced by two pov/ers, and they will 

 have nothing more to do but to analyfe that Motion in the fame way 

 in which they analyfe the moft fimple of all Motions, I mean that 

 in a ftraight line. In this way they will limplifythe fyftem exceeding- 

 ly, by giving up gravitation as well as projedion ; nor, indeed, do I 

 think they Ihould grudge to do this, after being obliged, as I have 

 fhown they are §, to give up projedion, which has always been 

 underftood to be neceiTarily conneded with gravitation. 



After 



* Vol. ii. p. 375. 



f See his words quoted, Vol. i. p. 547. 



X Vol. ii. p. 358. where I have given Sir Ifaac's own words, concerning this aflive 

 principle in Body ; See aJfo p. 376. ihld, where I have fliown the progrefs of Sir Ifaac's- 

 thoughts upon this fubje(n:. 



§ Pages 292. 293. 29S. 



