Chap. ir. ANTIENT METAPHYSICS. -^5 



ther Body, the Motion is not flopped by any obftacle or impediment, 

 but ceafes, merely by the Moving [-"ower ceafing to ad. 



Some of the Newtonians, with whom I have converfed, and who 

 are unwilling to give up this Firft Law of Motion, are very much a- 

 larmed with this inftance of Motion by Preffure, which, at the fame 

 time that it explains my notion of Motion by Mind, fhows evidently 

 that Sir Ifaac's Firft Law is not univerfal, even with refpe«ft to Mo- 

 tion produced by Body. They endeavour, therefore, to evade it, 

 by faying, that there can be no Motion by Trufion in "vacuo, but that 

 all the Motion there muft be by Pulfion ; for they fay, the reafon 

 why a Body, when only prefled by another Body, does not fly off 

 and go on by itfelf, is the Refiftence of the Medium. 



But to this I anfwer ; i wo. That there is no Space, fo far as we 

 know, in which there is no Refiftence ; for, in the celeftial regions, 

 there is light, which, though a very fubtile Body, muft refift in 

 fome degree, and therefore muft, fooner or later, put an end to the 

 Motion of the Planets, as I have obferved, if they were moved me- 

 chanically, as Sir Ifaac fuppofes. 2^0, The only confcquence of the 

 Refiftence of the Medium is to require a greater force of preffure to 

 move the Body than would be required in vacuo. But it is impof- 

 fible, I think, to conceive that a Body which is at reft in vacuo, and 

 which, by its nature and eftence, is as much difpofed to Reft there as 

 in plena, could not be put out of that natural ftate of inadivity by a 

 force fo gentle, as that the Body would not fly off, but continue to be 

 moved in conta(Sl: with the protruding Body ; or, if it fliould be drawn 

 gently, and not tugged violently, I cannot conceive that it would 

 overtake the Body which draws it, or continue in Motion after the 

 drawing Body has ceafed to move it. And, lajily. What can be an- 

 fwered to the inftance of unelaftic Bodies ? Will they fay that, in 

 vacuo, there is no diftindion betwixt elaftic and unelaftic Bodies, or 

 Vol. n. X X that 



