350 ANTIENT METAPHYSICS. Book IV. 



as was obferved before*, tbereare only two tbings whicb exifl: in tbat 

 way ; t'wic itfelf, concerning which we are inquiring, and motion '\, 

 Motion, therefore, is the meaftire we want ; which, when applied to 

 beings liable to change and fucceffion, is thus. 



But neither is this fufficiently determinate — For, hov/ is motion to 

 be made a meafure, fo as to be applied to the fubjeds of time ? This 

 Ariftotle has informed us of, by telling us, that we get the idea of 

 thiie^ by obferving what h fir/} and lajl in motion if: And, no doubt, 

 the interval betwixt what is firft and laft, in the movement of any 

 particular body, may be made a flandard or m.eafure, which will ap- 

 ply to any thing capable of being fo meafured. But, how are we ta 

 fix what is firft and laft in the motion of any body ; Suppofe the bo- 

 dy moves in a ftraight line, we may determine what is firft, if the line 

 has a beginning which we know ; and if it be not infinite, and that 

 we know the end of it, we can alfo determine the laft : But this will 

 only be a meafure while this motion lafts, and no longer ; whereas 

 time is underftood to be a perpetual meafure of duration. 



In order, therefore, to make motion the m.eafure we want, it is 

 required, . i7;;o, That the motion be perpetual. 2doy That it re- 

 volve into itfelf, and begin again at the fame point. 3//0, That 

 the duration of its revolutions be always the fame. With thefe re- 

 quifites, the motion of any particular body will be a meafure of 

 duration. But human art has hitherto contrived no fuch motion ; nor 

 has any natural motion been difcovered, with thefe requifites, except 

 the motions of the celefiial bodies; and, therefore, men, in all ages and 

 rations, have made their motions the meafure of duration ; particularly, 



the 



* Page 17T. 



ITime, fays Arlflotle, cannot be its own meafure ; x^n^ isx ^ae^KrtAt xi<>ii** Arlft. 

 Phyf. lib. 4. cap. 15. § 7. For, if it were its own meafure, what way could we define it ? 

 % Arift, PhyGc. lib. 4. cap. 16. § 6. 



