522 DISSERTATION ON 



downwards, the other centrifugal, by which it tends to go in a ftraight 

 line, according to the direftion in which it was at firft moved. But, 

 where there is no impulie or projedion, and no gravitation, but the 

 body is only moved forward in a curve, it is to me inconceivable how 

 it iliould have a tendency, either to the center, or from the center. 



I have infifled the more upon this example of projediles on earth, 

 that it was from them, as is generally believed, that Sir Ifaac took the 

 firft idea of his fyfiem. And it is no doubt true, that the motion of 

 the celeftial bodies may be analyzed into the motions which compofe 

 the motion of thefe projediles ; but, becaufe the motion of the celes- 

 tial bodies could be fo refolved, Sir Ifaac from thence too haftily con- 

 cluded, that they were actually fo combined, without attending to this 

 eflential difference betwixt the two motions, that the one was produced 

 by bodily impuUe, the other immediately and diredly by Mind. Add 

 to this another mofl: material difference, that, in projediles on earth,, 

 there are two n.oving powers quite diftind from one another ; the 

 one, bodily impulfe, by which the body is projected ; the other. Mind, 

 or whatever other power operates by gravitation. Now, that thefe two 

 powers, fo diff'erent, and ading fo differently, as to counteract one an- 

 other, Ihould produce a motion combined of different tendencies, is 

 no wonder. But it is to me altogether inconceivable, how one and 

 the fame power, ading upon the fame body, fhould give it two ten- 

 dencies at the fame time, fo different as the centripetal and the centrif* 

 fugal. 



4/0, That the different tendencies to and from the center of the ce- 

 leflial bodies moving in a circle or ellipfis, as well as of projediles 

 here on earth, are caufed by two different forces ading upon them; 

 and, that the centrifugal tendency is the effed of the projedile force, 

 and the centripetal of gravitation, is, I think, acknowledged by the 

 Newtonians, when they tell us> that, if the projedile force be great, 



and 



