THE^NEWTONIAN PHILOSOPHY. ^43 



motion will depend upon the force of the Impulfe : So that, with re- 

 fpedt to two bodies that are moved in vacuo^ the continuance of the 

 motion of the one will be to the continuance of the motion of the o- 

 ther, caeteris paribus^ as the force of the impulfe by which the one is 

 moved is to the force of the impulfe by which the other is moved. 



Thus, it appears, that the continuance in motion, of bodies, moved 

 by pulfion, may be accounted for, without having recourfe to the 

 atheiftical fyftem of matter moving itfelf, and without y^/^m«^ hy^ 

 pothefes *, but according to the general analogy of nature ; for, 

 if the principle of motion, in the iron^ (not to mention the other in- 

 ftances I have given), be excited, and put in exertion, though before 

 latent, by the loadftone being preiented to it, Why (hould not the 

 principle of motion be excited in any body by pulfion ? And there 

 is only this difference betwixt the two cafes, that we cannot fo eafily 

 give a reafon for the phaenomenon of the iron being put in motion 

 by the loadftone, as we can do for the other ; for, as to the other, if 

 the one body, ftriking againft the other, were only to produce a mo- 

 tion as momentary as the impulfe which caufes it, neither the bufi- 

 nefs of nature, nor of art here below, could be carried on. 



And here we may obferve, both in the iron attracted by the mag- 

 net, and the body impelled continuing in motion, that the principle 

 of motion, in each of them, by which they tend towards the center of 

 the earth, operates conftantly and incelTantly ; whereas, the principle 

 by which the one is moved towards the iron, 'and the other continues 

 to be moved, after the pulfion Is ceafed, operates only occafionally. 

 And from hence, I think, wc may infer, that neither of them adls 

 eternally. But, as the one ceafes to a<5l when the iron is united to 

 the loadftone, fo the other ceafes to a£l when the body has gone far 

 enough to anfwer the purpofes of nature. 



CHAP' 



• * Hypothfes nonJingOf fays Newton, in his Scholium Gencrak. 



