Cliap. I. APPENDIX. 293 



ftraiglit line, and a much more conftant motion, and which appears 

 to be more eflential to Body than this motion by the 'uis inftta^ And, 

 if fo, I fhould defire to know why gravitation fhould not be eflen- 

 tial to Matter, and produced by a vis hifita^ as well as the Motion. 

 of a body projected ? 



Moreover, the planet, in the cafe fuppofed, will, by Its centrifu- 

 gal force, have a tendency to move, not only in a ftraight line, but 

 with an equable velocity. Now, this may be conceived, if the pla- 

 net had been projedied :. For then It might have been moved in both 

 ways ; and it might be faid that it only retained the Motion that 

 had been once imprefled upon it. But, if it can begin a new Mo- 

 tion, quite different from the old in the elliptical line, not only in 

 its diredion but in its equability, (the ellipncal Motion varying ia 

 every inftant), and all this by a power innate and eflential to it, I 

 do not know what Body may not do by its natural powers. 



Nor can the Centrifugal Motion of the Planet, in the cafe I have 

 fuppofed, be fupported by fad: and obfervation, any more than by 

 theory. In the cafe of other Centrifugal Motions, fuch as that of a ft:orre 

 in a fling, the Motion is produced by the adion of Body upon Body, 

 and by therepeatedprojedion of the fl:one, which makes it at laft fly off 

 with great force *: And, accordingly, Sir Ifaac has ufed the example 

 of a fling to illufl:rate his theory of the Planetary Motion t, and very 

 properly upon liis hypothefis of the Planet being firfl: projeded be- 

 fore it is moved in an cllipfis. But where the Motion is begun 

 by Mind, and not in a ftraiglit line, but in a curve, as in the 

 cafe I fuppofe, it will not be pretended to be proved by any expe- 

 riment, that, if the Body ceafes to be moved in a curve, it will by 

 the njis infita be moved in a ftraight line ; but, on the contrary 

 daily experience and obfervation fliows that it will not. 



Having 

 * See what I have faid concerning the Motion of a flone in a fling, Vol. ij. p. 4-'^. 

 t Vol. i. p. 524. 525. 



