2go APPENDIX. Chap. I. 



cffea of the original impalfe, or vis impreffa, upon the body, and 

 that there was no need to have recourfe to any vis infita : And, ac- 

 cordingly, it is againft this opinion that I have argued in the fifth 

 book of my fecond volume *. But, upon further inquiry, and con- 

 verfing with men more learried in the Newtonian philofophy, I find 

 that it was not only the opinion of Sir Ifaac that the Motion was 

 carried on by a vis infita, which he has exprefsly diftinguifiied from: 

 the vis imprejfa^ but that it is impoffible, without the vis infita^ to 

 account for the vis centrifuga of the planet, by which it has a con- 

 flant tendency, in every part of its orbit, to go off in a ftraight 

 line ; fo that, if the centripetal force were to ceafe at any point of 

 the orbit, the body would go on, not in the curve but in the tan- 

 gent, at that point, and which may be in a direction quite different 

 from the line in which it got the original impulfe ; for the fine of 

 this tangent may be either parallel to the line of original diredtion, 

 or perpendicular, or oblique to it. Now, this is abfolutely inconcei- 

 vable, if the Motion be carried on by virtue of one impulfe j for, ia 

 that cafe, it muft go on in the fine in which it was originally pro- 

 jeded, and in no other. 



Before I come to inquire into the confequences of an opinion 

 which afcribes to matter a power of moving itfelf in fo many differ- 

 ent diredlions, it is proper to confider how the Progreflive Motion 

 of the Planets began. That Sir Ifaac, when he wrote his Principia, 

 fuppofed that it began by a bodily impulfe, I think, is evident f j but 

 his followers, at prefent, are generally of opinion that it began by 

 Mind : And, indeed, if a man is not an abfolute materialift, he muft 

 admit that Mind is originally the author of all Motion ; and, if fo, 

 why fliould not he fuppofe that Mind has produced the Planetary 

 Motion immediately and directly, without the intervention of other 



Bodies, 



* Vol. II. p. 340. 

 I Ibid. p. 320. 



