Chap. III. ANTIENT METAPHYSICS. 349 



I hope, by this time, the reader is at leaft convinced that this Lav/ 

 of Motion is not an Axiom, or Self-evident Propolition, but a Pro- 

 pofilion that needs to be proved ; and by how much the more pa- 

 radoxical it is, fo much the clearer proof it will require. It is im- 

 poflible, by the nature of things, to prove it by experiment : And yet 

 the only proof, that is offered of it, is a kind of indirect proof by the 

 experiment of a pendulum fwinging in an exhaufled receiver, where, 

 they fay, (and it is no doubt true), that it will fwing much longer than 

 if it were in the air; from whence they infer, that, if a perfedl -ua' 

 cuum could be made, it would, continue to vibrate forever. But this 

 is plainly begging the queftion, unlefs they could prove that the Mo- 

 tion decreafes and languifhes exa<£tly in proportion to the obftruftioa 

 of the Medium. But this I hold to be impoflible ; at leaft, no me- 

 thod of calculation has yet been found out, for difcovering accu- 

 rately the c^e(X of the different denfrties of mediums upon Bodies ia 

 Motion. It is not, therefore, by Experimental Philofophy, as it is 

 called, but by Metaphyfics, or the Fir/l Philofophy, as I have faid 

 which explains the nature of Body and Motion, that this queftion is 

 to be determined ; and upon the principles of that philofophy, I fay, 

 not only that it is not true, but that it is impoflible to be true. 



And, for this purpofe, I will aflume only three propofitions, which 

 I think muft be granted. The firft is, what I have already men- 

 tioned, and which every Newtonian will readily alfent to. That 

 Body, by its nature and eflence, is peifedly inadive and inert, and 

 therefore it cannot move itfelf, but muft be moved by fome other 

 thing, external or internal. The fecond, alfo, I have already men- 

 tioned. That Motion has nothing fixed or permanent in its nature, 

 but its very effence and exiftence is by fucceflion. And the third is, 

 what hitherto has not been mentioned, but has been acknowledged 

 by all natural philofophers, antient and modern, That there is a 



Caufc 



