PRELUDE TO THE EPOCH OF NEWTON. 159 



formed a part of the studies of that place. Indeed, 

 Rohault's Physics was used as a class-book at that 

 University long after the time of which we are 

 speaking; but the peculiar Cartesian doctrines 

 which it contained were soon superseded by others. 

 With regard, then, to this part of the discovery, 

 that the force of the sun follows the inverse dupli- 

 cate proportion of the distances, we see that several 

 other persons were on the verge of it at the same 

 time with Newton ; though he alone possessed that 

 combination of distinctness of thought and power 

 of mathematical invention, which enabled him to 

 force his way across the barrier. But another, and 

 so far as we know, an earlier train of thought, led 

 by a different path to the same result ; and it was 

 the convergence of these two lines of reasoning that 

 brought the conclusion to men's minds with irre- 

 sistible force. I speak now of the identification of 

 the force which retains the moon in her orbit with 

 the force of gravity by which bodies fall at the 

 earth's surface. In this comparison Newton had, so 

 far as I am aware, no forerunner. We are now, 

 therefore, arrived at the point at which the history 

 of Newton's great discovery properly begins. 



