302 HISTORY OF CHEMISTKY. 



gous to that in which mechanical forces are balarced against each 

 other by the intervention of the lever. It is impossible to him 37 to 

 resist the idea, that the voltaic current 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, possessed the 

 idea of pressure, and were thus able to found the science of morh:;- 

 nics. 38 'And when he cannot obtain these distinct modes of concep- 

 tion, 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 

 .^dted is the thought. This conception of Chemical Affinity as a 

 peculiar influence of 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 conveyed, I venture to 

 trust that I shall be held to have given a faithful account of this im- 

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

 subject, notice one or two of the remarkable subordinate features of 

 Faraday's discoveries. 



Sect. 3. Consequences of Faraday's Discoveries. 



FARADAY'S volta-electrometer, in conjunction with the method he had 

 aiready employed, as we have seen, for the comparison of voltaic and 

 common electricity, enabled him to measure the actual quantity of 

 electricity which is exhibited, in given cases, in the form of chemical 

 affinity. His results appeared in numbers of that enormous amount 

 which so often comes before us in the expression of natural laws. One 

 grain of water 40 will require for its decomposition as much electricity 

 as would make a powerful flash of lightning. By further calculation, 

 he finds this quantity to be not less than 800,000 charges of his 

 Leyden battery ; 41 and this is, by his theory of the identity of the 

 combining with the decomposing force, the quantity of electricity 



37 Art. 950. 38 990. 39 1114. 40 153. " Sfil 



