Chap. XIX. ANTIENT METAPHYSICS. 273 



Thus, it appears that Sir Ifaac's aftronomy, inftead of afligning the 

 caufc of the motions of the heavenly bodies, lays down X.\vo/a^s as 

 pojiulatay which he defires fhould be granted to him, but which arc 

 neither neccflary nor probable. If, indeed, it could be proved, that 

 the circular motion is aciually combined of a centrifugal and centri- 

 petal tendency, both thefe hypothefes would have been altogether un- 

 necelTary. But this, 1 am perfuaded, was not the opinion of Sir Ifaac 

 himfelf ; nor do I know that it has been advanced in print by any of 

 his followers : I muft, therefore, till I am better informed, hold the 

 antient opinion to be the truth, that the circular motion is afimple un- 

 <:ompounded motion. 



But, even upon this fuppofition, Sir Ifaac, I think, was not driven to 

 the neceffity of his two hypothefes ; for, though the circular motion of 

 the celeftial bodies be not aBually compounded of gravitation and pro- 

 jection, there is nothing to hinder it to be refolved or analyzed in- 

 to thefe two motions in different dire<flions, in the fame manner as 

 the motion of projeCtiles on earth is analyzed ; for the redilineal mo- 

 tion, though mofl perfedly fimple, may be analyzed into two motions, 

 in the diredion of two lines forming the fides of a parallelogram, of 

 which the line of the body's motion is the diagonal^ without the leafl: 

 neceffity of fuppofing, that the redilineal motion was adually produ- 

 ced by two forces ading in the diredion of the two fides of the paral- 

 lelogram, or that it has any tendency to go anywife out of a ftraio-ht 

 line, either to the right or left *. In this way, all Sir lfaac*s demon- 

 ftrations and calculations, arifing from the refolution of the motions of 

 the celeftial bodies, will ftand upon as firm a bafis as ever, and his 

 fyftem be much more fimple and plain, being difencumbered of two 



M m hypo- 



• See Mf M«Laurm upon the Philofophical Difcoveries of Sir Ifaac Newton, 

 book II. chap. 2. p. 121. X22. and 157. 



