Chap. XV. ANTIENT METAPHYSICS. 187 



As to the motion of the planets, it is fiippofed by the new philofo- 

 phy, to be compofed of two motions, the one a projeftilc motion^ and 

 the other an attra&ive : And the hypothefis Is, that they were at firfl: 

 moved by God Almighty, in aftraight line; but that, by iheattradion 

 of the fun counterading this redilineal motion, they are moved in an 

 ellipfis round the fun. But this, as 1 have faid, is mere hypothefis ; 

 for, in the firft place, how can it be known that they were at firfl: im- 

 pelled in a ftraight line, and did not move from the beginning in the 

 fame way they do at prefent ? -i^/fyy There is no reatbn to fuppofe 

 that the fun attrads them, though they are moved round him, any 

 more than to fuppofe that, becaufe I go round a certain objed, I am 

 attraded by it *. 



If, therefore, we will renounce hypothefis, and fpeak no more of 

 combined motions ^ or of centripetal and centrifugal force^ but adhere to 

 the plain fad:, which is fimply this, that bodies move in different di- 

 rections, and by different kinds of motion, it only remains to be in- 

 quired, What is the caufe efficient of thofe various motions ? Whether 

 it be immaterial, as I fuppofe it to be, or material ? for one or other 

 of them it mufl: of neceffity be. And we are fo far advanced in the 

 inquiry, as to have difcovered that, if it be material, it muft neceffariiy 

 operate by the body moving impelling the body that is moved. 



Now, in the firft place, I fay, in point of fad, that there are no 

 phaenomena which lead us to believe, that either a (lone falls to the 

 ground, or the celeftial bodies are moved, by any external i.iipulfe of 

 other bodies. I know that Sir Ifaac Newton did attempt to account 

 for thefe motions, by a certain fubtile fluid, which he thought was 

 fufKcient to produce fuch wonderful effcds. But, 1 believe, all his 



A a 2 followers 



• See wliat 1 have faid on this fubjeft in the preceding note, and what I fliall fay 

 fuithei upon it in another chapter of thii book. 



