EPOCH OF DAVY AND FARADAY. 191 



which mechanical forces are balanced against each 

 other by the intervention of the lever. It is impos- 

 sible to him 37 to resist the idea, that the voltaic cur- 

 rent must be preceded by a state of tension in its 

 interrupted condition, which is relieved when the 

 circuit is completed. He appears to possess the 

 idea of this kind of force with the same eminent 

 distinctness with which Archimedes in the ancient, 

 and Stevinus in the modern history of science, pos- 

 sessed the idea of pressure, and were thus able to 

 found the science of mechanics 38 . And when he 

 cannot obtain these distinct modes of conception, 

 he is dissatisfied, and conscious of defect. Thus in 

 the relation between magnetism and electricity 39 , 

 " there appears to be a link in the chain of effects, 

 a wheel in the physical mechanism of the action, as 

 yet unrecognized." All this variety of expression 

 shows how deeply seated is the thought. This con- 

 ception of chemical affinity as a peculiar influence 

 or force, which, acting in opposite directions, com- 

 bines and resolves bodies ; which may be liberated 

 and thrown into the form of a voltaic current, and 

 thus be transferred to remote points, and applied in 

 various ways ; is essential to the understanding, as 

 it was to the making, of these discoveries. 



By those to whom this conception has been con- 

 veyed, I venture to trust that I shall be held to 

 have given a faithful account of this important event 

 in the history of science. We may, before we quit 

 37 Art. 950. ** 990. 39 1114. 



