4i6 ANTIENT METAPHYSICS. Book V, 



Now, there is a Motion on Earth well known, which has an extra- 

 ordinary likenefs to the Motion of the Planets. The Motion I mean 

 is that of Projediles ; for the figure they defcribe is a Parabola, which 

 is a Sedlion of the Cone, As well as the Ellipfe, and has the fame 

 Centre as the Moon, I mean our Earth. Further, as Sir liiiac has 

 demonftrated, if the Projedlion were of fufficient force, the Pro- 

 jedile would go round our Earth as the Moon does ; — and lauly, 

 not to mention other refemblances, the fall from the Tangent, 

 in any Arc defcribed by the Projeftile, is the fame in the fame 

 time, as if it had fallen diredly from the Tangential Point, it is 

 with this lafl refemblance that we are moft concerned at prefent ; 

 for, if we can determine by what Law any heavy Body here on 

 Earth falls from any height direftly to the Earth, and if it be true 

 that there is any Sympathy betwixt things above and things below 

 (according to the antient faying), that is, any general rule governing 

 the Motion of defcending Bodies both in the Heavens and here, we 

 ihall, at the fame time, determine the Law of the Defcent of the 

 Moon from the Tangent. 



And here Sir Ifaac has ufed a Difcovery, made by Galileo before 

 him, concerning the defcent of falling Bodies on Earth. Gahleo 

 found out that the Motion of thcfe Bodies was not equable, but 

 the Velocity increafed as the Times, fo that, in a tloubie Time the 

 Velocity was double. 



But this rule Sir Ifaac found would not apply to the Defcent of the 

 Moon ; and having difcovered that the Defcent of the primary Pla- 

 nets towards the Sun, was as the Squares of the Diftances reciprocally, 

 he conjectured that the fame might be the Law of defcending Bodies 

 on Earth, but which Galileo had not difcovered, nor indeed could 

 difcover, by fadl and obfervation on falling Bodies here, as he had dif- 

 covered the acceleration in the Ratio of the Times. Suppofing, therefore, 



that 



