EPOCH OF DAVY AND FARADAY. 179 



It will not be necessary to say much on the 

 theories of the voltaic pile, as separate from other 

 parts of the subject. The contact-theory, whieh 

 ascribed the action to the contact of different metals, 

 was maintained by Volt a himself; but gradually 

 disappeared, as it was proved (by Wollaston 6 espe- 

 cially,) that the effect of the pile was inseparably 

 connected with oxidation or other chemical changes. 

 The theories of electro-chemical decomposition were 

 numerous, and especially after the promulgation of 

 Davy's Memoir in 1806 ; and, whatever might be 

 the defects under which these speculations for a long 

 time laboured, the subject was powerfully urged on 

 in the direction in which truth lay, by Davy's dis- 

 coveries and views. That there remained some- 

 thing still to be done, in order to give full evidence 

 and consistency to the theory, appears from this ; 

 that some of the most important parts of Davy's 

 results struck his followers as extraordinary para- 

 doxes ; for instance, the fact that the decomposed 

 elements are transferred from one part of the cir- 

 cuit to another, in a form which escapes the cogni- 

 zance of our senses, through intervening substances 

 for which they have a strong affinity. It was found 

 afterwards that the circumstance which appeared 

 to make the process so wonderful, was, in fact, the 

 condition of its going on at all. Davy's expres- 

 sions often seem to indicate the most exact notions: 

 for instance, he says, " It is very natural to suppose 

 c Phil. Trans. 1801, p. 427, 



N2 



