THE ELECTRO-MAGNETIC ENGINE. 23 



mechanical effect, evincing the convertibility of the 

 mechanical effect expended into the effect of the current 

 which it produced. By the second, mechanical effect is 

 produced as the effect of the electric current, evincing 

 with the first machine the reciprocal convertibility of the 

 two effects ; and besides this, since the current originates 

 in the zinc electrolyzed in the battery, showing the con- 

 vertibility of the effect of chemical combination as effected 

 by electrolysis and the mechanical effect produced. 



Clear and direct as this evidence now appears, it was by 

 no means clear in 1838, as is shown by the fact, that, except 

 by one "man," it was not definitely recognized for twelve 

 years, and then only as the result of this man's teaching, no 

 one in the meantime having perceived it. 



This obscurity was, doubtless, owing to the general 

 interest in electricity at that time being in the phenomenal 

 effects rather than the quantitative, and in the absence of 

 any common language in which to express the latter. 

 Quantitative expressions for electricity had been used by 

 various investigators, but they were not by any means 

 uniform, each investigator using his own expressions, 

 which were little known ; the significance of the quantitative 

 measures being still less apprehended. Thus Ohm had 

 shown that the electrical action of a battery in overcoming 

 the electrical resistance of the circuit, was always pro- 

 portional to the product of the quantity of current 

 multiplied by the electromotive force of the elements used. 

 Faraday had shown that the quantity of current was 

 proportional to the number of chemical equivalents electro- 

 lyzed. Thus, from Ohm and Faraday together, it was to 

 be inferred that the electric action of a battery in over- 

 coming the resistance of the circuit is proportional to the 



