sect, iv.j DISSERTATION SECOND. 101 



Ilooke did not stop short in the same unaccountable man- 

 ner, but made a nearer approach to the truth than any one 

 had yet done. In his attempt to prove the motion of the 

 earth, published in 1674, he lays it down as the principle on 

 which the celestial motions are to be explained, that the 

 heavenly bodies have an attraction or gravitation toward 

 their own centres, which extends to other bodies within the 

 sphere of their activity ; and that all bodies would move in 

 straight lines, if some force like this did not act on them 

 continually, and compel them to describe circles, ellipses, or 

 other curve lines. The force of gravity, also, he considered 

 as greatest nearest the body, though the law of its variation 

 he could not determine. These are' great advances ;■ — 

 though, from his mention of the sphere of activity, from his 

 considering the force as residing in the centre, and from his 

 ignorance of the law which it observed, it is evident, thai 

 beside great vagueness, there was much error in his notions 

 about gravity. Hookc, however, whose candour and up- 

 rightness bore no proportion to the strength of his under- 

 standing, was disingenuous enough, when Newton had deter- 

 mined that law, to lay claim himself to the discovery. 



This is the farthest advance that the knowledge of the 

 cause of the celestial motions had made before the investiga- 

 tions of Newton ; it is the precise point at which this know- 

 ledge had stopped ; having met with a resistance which re- 

 quired a mathematician armed with all the powers of the 

 new analysis to overcome. The doctrine of gravity was yet 

 no more than a conjecture, of the truth or falsehood of which 

 the measurements and reasonings of geometry could alone 

 determine. 



Thus, then, we are enabled accurately to perceive in 

 what Newton's discovery consisted. It was in giving the 

 evidence of demonstration to a principle which a few saga- 

 nous men had born sufficiently ?harp-sighted to see obscure- 



