INFLUENCE ON RECENT SCIENCE 105 



sons from these assumptions, afterwards on inward 

 sentiments of knowledge, as they are called, instead of 

 clear and real ideas, lays aside, at once, the only sure 

 guides to knowledge. This Descartes did very widely 

 in his construction of a world, and yet by dint of genius 

 he gave a great air of simplicity and plausibility to his 

 hypothesis, and he knew how to make even geometry 

 subservient to error. . . . The plenum of Descartes 

 is well-nigh destroyed ; many of his laws of motion are 

 shown to be false; the mills that served to grind his 

 three elements are demolished : and his fluid matter in 

 which, as in a torrent, the planets were carried around 

 the sun, whilst a similar motion in the particular vortex 

 of every planet impelled all bodies to the center, is 

 vanished. Notwithstanding all this, how slowly, how 

 unwillingly have many philosophers departed from 

 the Cartesian hypothesis?" 



That Bolingbroke was mistaken when he says that 

 the plenum, the vortices, and all the other apparatus 

 of Descartes have been destroyed, can be readily seen 

 by reading any modern treatise on physics. 



But he was vividly correct in the larger and more 

 important part, when he finds that all such hypotheses 

 are based on an inward sentiment of truth and not on 

 clear and real ideas. An inward sentiment of knowl- 

 edge is and must be the final guide of anyone who em- 

 ploys this hypothetical method, for how can anyone 

 have clear and real ideas about such things as tran- 



