4c6 A N T I E N T M E T A P H Y S IC &. ■ feook V. 



That fiot abfolide^ but relative to two things. Time and Space — Jf 

 the Motion be equable in a Straight Line, and the Time of it be 



■ kiiGivn, the Law of the Motion /j obvious. — But if the Amotion be in a 

 Curve and not equable, though the 'Time be known, the Law of 

 the Motion not eafy to be difcovered. — The Force mujl be eftimated 

 by a Motion in a Straight Line, one or more. — But hoxv apply Mo- 

 tion in a Straight Line to a Curve ? — This tmpoffikle to be done, if no 

 Straight Line could be difcovered neceffarily refulting from the Na- 

 ture of the Motion. — Butfuch a Straight Line has been obfcrved in 

 the DefccJit of the Planet from its Tangent. — This Line obferved 

 IV! th refpcEl to the Moons Dcfcent from her Tangent. — The Length 

 of this Line known : — The fame as if the Moon had defended direSlly 



from the Tangential Point. — The Law of this Motion of Defcent 

 wotdd be known, if the Motion was equable — but the Motion is un- 

 equable.— -i^jr difcovering the Law of this unequable Motion, ;v- 

 courfc nufl be had to a ftmilar Motion oji Earth, the Motion of the 

 Projectile. — The Law of the Defcent of the Projected Body afcer- 

 tained, firf by GalileoV Difcoveries, and then by Sir li'aacV. — Sir 

 Kaacfr/l difcovered that the Defcent of falling Bodies was both be- 

 gun and accelerated in the Ratio of the Diftunce from the Centre 

 invcrfely. — This could not have been difcovered by Padi; and Obfer- 

 vation here on Earth, but it was itferred from the Defcent of the 

 Moon. — The Theory of Gravitation in this Way generalised by vyix 

 Ilaac, and its Law difcovered. — How the Theory of Gravitation, 

 thus made general, is to be applied to the Planets. — The Motion of the 

 V\z.\\Q\.^ fuppcfcd by Sir Ifaac to be compounded, as he fuppofed that of 

 Proje£liles to be, — The two Motions are, the one in the Line o/'Pro- 

 jedion, the other in the Line of Gravitation. — The Motion of the 

 Planets not adlnally combined, but only fuppofed to be fo for the fake 

 of Dcmonf ration. — Afimple uncompounded Motion of the Planets is, 

 by its Nature, poj/ible. — Iff, all the Properties of the Motion are 



from thence deducible, though we may not be able to make the Deduc- 

 6 tion.'— 



