THE NEWTONIAN PHILOSOPHY. 523 



and the gravitation fmall, then v;ill tlie cuiviture of the circle be 

 ffnall, and nearer to the ftraight line. If, on the contrary,, the gravi- 

 tating force be great, and the projectile fmall, then will the curviture 

 of the orbit be greater, and recede farther from the tangent or ftraight 

 line ; for, fay they, efreds muft be proportional to their caufes * ; 

 which is plainly faying, that the projection is the caufe of the centri- 

 fugal tendency, and gravitation of the centripetal : So that, if there 

 were neither projection nor gravitation, there would be neither cen- 

 trifugal nor centripetal tendency. 



5/0, Whether the motioa was from all eternity, or had a beginning 

 iu time, can make no difference as to the nature of the motion. Sup- 

 pofing, then, the motion never to have had a beginning, there could 

 have been no projection, and, if no projedion, no centrifugal ten- 

 dency ; as it has been fhown that this tendency is produced by 

 the projection, and is greater or lefs, in proportion to the projeCtilc 

 force : And, if there be no centrifugal tendency, there can be no cen- 

 tripetal ; it being impoffible to conceive that, in the circular motion, 

 there can be the one without the other. And this is another proof, 

 that, from the nature of the motion merely, there arifes neither of the 

 two tendencies. 



btOj If it were admitted that, by tlie nature of the circular motion, 

 the body had a tendency to go to the right and to the left — to the 

 center and from it ; yet, even this admifhon would not ferve the 

 purpofe of Sir Ifaac ; for his mechanifm of the heavens requires, that 

 he fhould likewife prove, that, by the nature of the motion, the body 

 has fuch a tendency to go out of the circle on one fide, that, if it were 

 not reftrained, it would fly off in a tangent, and continue its motion 



U u 2 in 



* See Sir Ifaac*s Principia, vol. i. clef. 5. with the Commentaries of Thomas Lc 

 Seur, and Frances Jacquier, 



