Chap. V. A N T I E N T M E T A P H Y S I C S. 389 



fuch figure being truly no more than a polygon of a great number 

 of fides. 



As, however, it cannot be denied that a polygon, fuch as that into 

 which Sir Ifaac has analyfed the orbits of the planets, may be defcri- 

 bed by Mind as well as Bodily Impulfe, fince Mind can move Body 

 in a ftraight line as well as in a curve, or that, in fome way or o- 

 ther, the Motion of the planets, though produced by Mind, may be 

 compounded, I will examine that queftion, and, for that purpofe, 

 will begin with laying down fome general pofitions concerning 

 fimple and compounded Motion. 



By z fimple Motion^ \ mean a Motion produced by one Moving 

 Power a£ting conftantly and indefinently, by which the Body is mo- 

 ved either in a ftraight line or in a curve. If there be feveral Mo- 

 ving Powers, but all acling in the fame way and in the fame direc- 

 tion, fo that they only afTift one another, as when feveral perfons 

 pufh or draw a Body in the fame diredion, I confider thefe powers, 

 thus co-operating and affifling each other, as but one power. On the 

 other hand, the Motion is compounded, — Firjl^ when the Motion is 

 interrupted, fo as not to go on conftantly, but to be diftinguifhed 

 into parts by perceptible intervals ; — Secondly, When the Motion 

 does not defcribe one line, whether ftraight or curve, but feveral 

 lines, fo as to make a figure of feveral fides, like that into which Sir 

 Ifaac analyfes the Elliptical Motion. Of this kind, according to the 

 Jefults, all Motion, though apparently in a curve line, muft be. — 

 Thirdly, When the Body in Motion is adcd upon by two or more 

 powers moving the Body different ways, fo as not to co-operate but 

 to counteract one another. 



Thefe are all the ways in which, I think, it is pofTible that the 

 Motion of a Body can be compounded : Let us now confider in which 



o£ 



