Experimental Researches in Electricity. 99 



fluids known, except such as contain water, which are capa- 

 ble of being made the medium of connexion between the me- 

 tals or metal of the voltaic apparatus." Faraday's fourth 

 series of researches completely settles this point, by shew- 

 ing that there are hundreds of bodies equally influential with 

 water in this respect, and that the latter is therefore only 

 one of a numerous class of substances, instead of being the only 

 one and essential. He conceives that its exclusive character 

 was obtained in consequence " of the general necessity of a 

 fluid medium," of its being the only one of this class of bo- 

 dies existing fluid at common temperatures, " its abundant 

 supply as the great natural solvent," and its constant use in 

 that character in philosophical investigations, because of its 

 having a smaller interfering, injurious, or complicating action 

 upon the bodies either dissolved or evolved, than any other 

 substance. 



Having determined the preceding points, Faraday proceeds 

 to the question of theories of electro-chemical decomposi- 

 tion, and he premises the developement of his own, by a 

 brief account of those of others, in so far as he is personally 

 acquainted with them. On these theories we do not now in- 

 tend to decide, as incidental notices of their leading features 

 will necessarily be introduced when discussing that proposed 

 by Faraday, and more than simple notices is unnecessary. 



" That electro-chemical decomposition," Faraday remarks, 

 " does not depend upon any direct attraction and repul- 

 sion of the poles, (meaning thereby the metallic termina- 

 tions, either of the voltaic battery or ordinary electrical 

 machine arrangements,) upon the elements in contact with 

 or near them, appeared very evident from the experiments 

 made in air, when the substances evolved did not collect 

 about any poles, but in obedience to the direction of the 

 current, were evolved, and I would say, ejected, at the extre- 

 mities of the decomposing substance. But notwithstanding 

 the extreme dissimilarity in the character of air and metals, 



