52d DISSERTATION ON 



Now, if a circular motion can be produced in this vvavi any motion 

 of the fame kind, though not produced in the fame way, but refulting 

 ftom the operation of Mind, may be refolved or analy(ed in the fame 

 way ; juft as motion in a ftraight hne, though produced by one lingle 

 impulfe, and therefore perfe^lly fimple, may be refolved into two 

 forces adding in the diredion of the two fides of the parallelogrami 

 of which the ftraight line is the diagonal. And this Is a refolution 

 of the motion in a ftraight line, which Sir ifaac. has. ufed very much *. . 



It, is, therefore, I think, true, what I have obferved eJfewhere t> 

 that this refolution or analyfis of the circular motion will ferve Sir 

 Ifaac's purpofe, without embarrafling his fyftem with hypothefes of 

 projection and gravitation, centripetal and centrifugal forces ; for, if 

 the motion can be refolved" into thefe two powers of projedion and 



gra- 



ever, was never publiflied. If there were any defe£l there, I doubt it would overturn 

 the whole theory of proje£lion and gravitation : But this I leave to the confuieration 

 of the geometers, and of thofc who are learned enough in fluxions, to underftand Mr 

 M'Laurin's defence of them. 



* See thej^r/? propofition of fe£lion 2d, book ifl:,'^and the/^r;?;;^ propofition of the 

 fame fedtion. I have been told, that, from thefe two propofitions, it may^be inferred, 

 that the circular motion is, by its nature, combined : But, in the hrfl of thefe propofi- 

 tions, he only demonftrates, that a body, moved in a circle round an immoveable 

 centre, will, by radii drawn from the circumf rence to the center, defcribe jireas pro- 

 portionable to the times of the motion : AnAy in the fecond propofition, that, if a body 

 moved in any curve line, defcribe areas, formed by radii drawn towards any point, 

 proportionable to the times, the body is impelled by a centripetal force towards the. 

 fame point.. And it is evident that both the propofitions are demonftrated by the re- 

 folution of the circular motion into the motions of projedlion and gravitation : So that 

 the demonllrations plainly fuppofe, what indeed is the hypothefis of the whole book, 

 that all motion is primarily and originally in ftraight liaies, being produced by bodily 

 impulfe, which certainly can produce no other motion, unlefs when two fuch motions, 

 in a ftraight line, are combined in the manner Sir Ifaac fuppofes.' — In fiaort, throug{i 

 the whole Principia, he treats of no other motion but that which is produced by body 

 operating upon body : And his notions appear to me to have been fo grofs, and fo 

 little raifed above m?tter, that he had no idea of any moving power, except that aloue 

 which Is perceived by fcnfej I mean body, 

 t See page 237. 



