440 ANTIENT METAPHYSICS. Book V. 



vious that, In the Planetary Orbit, it was neccfTary there fliouKl he 

 a fall from the Tangent, and which, it may be obferved in pafling, 

 is probably the rcafon that fome have imagined the Circular or 

 Elliptical Motion was compounded, and produced by diiTerent Pow- 

 ers ading upon the Body, not diftinguifhlng rightly betwixt a Mo- 

 ving Power internal and eflential to the Motion, and that which 

 is external. ido^ It is equally obvlour-, that this fall from the 

 Tangent, as well as the Moving Force, by which the Planet is car- 

 ried on In Its Orbit, muft nccefTarily depend upon the diameter of 

 the Orbit, or, in other words, the diftance of the Planet from Its 

 Centre, and, confequcntly, muft needs have fome relation or ratio 

 to that diftance. 3//0, The refemblance betwixt the Elliptical Mo- 

 tion of the Planets, and the Parabolic Motion of Projedlles, mufl: 

 have been fo well known to fo great a Geometer and Mechanic as 

 Sir Ifaac, that It was no wonder If he endeavoured to inveftlgate the 

 Laws of the one Motion by thofe of the other, and, being enabled 

 by the help of Galileo's difcoveries, to afcertain exadlly the defcent 

 of the Projedlle in its Curvilineal Motion, and, by confequence, Its 

 progreffive Force, it was moft natural for him to apply the Laws of 

 the Motion of the Projedile to the Planetary Motion,, and finding 

 that the phaenomena perfedly agreed with thefe Laws, to conclude 

 from thence that the Laws of the two Motions were the fame. 



But though, by thus comparing the two Motions, the Law of the 

 Planetary Motion has been difcovered, yet that comparlfon has led 

 the Newtonians Into the errors which I have obferved in their fyftem : 

 And, _yf/y?, as the two Motions agree in fo many things, they have 

 been led to believe that they agreed In every thing, and, particu- 

 larly, that they both began in the fame way, that Is, by Impulfe ; 

 whereas, there is nothing in the nature of things to hinder that they 

 may have had different origins, and yet be governed by the fame 

 Laws. If, indeed, they had not only begun differently, but had 



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