ELECTRICITY IN MOTION. 85 



pensation be supposed to take place, from the effects of induced 

 electricity. Instead of the extrication of hydrogen, the same 

 causes will sometimes occasion a deposition of metal which has 

 been dissolred, will prevent the solution of a metal which would 

 otherwise have been corroded, or produce some effects which ap- 

 pear to indicate the presence of an alkali, either volatile or fixed. 

 All these operations may, however, be very much impeded by the 

 interposition of any considerable length of water, or of any other 

 imperfect conductor. 



It is obvious, that since the current of electricity, produced by 

 a galvanic circle, facilitates those actions from which its powers 

 are derived, the effect of a double series must be more than twice 

 as great as that of a single one : and hence arises the activity of 

 the pile of Volta, the discovery of which forms the most important 

 era in the history of this department of natural knowledge. The 

 intensity of the electrical charge, and the chemical and physiolo- 

 gical effects of a pile or battery, seem to depend principally on 

 the number of alterations of substances; the light and heat more 

 on the joint magnitude of the surfaces employed. In common 

 electricity, the greatest heat appears to be occasioned by a long 

 continuation of a slow motion of the fluid ; and this is perhaps 

 best furnished in galvanism by a surface of large extent, while 

 some other effects may very naturally be expected to depend on 

 the intensity of the charge, independently of the quantity of charged 

 surface. It may easily be imagined, that the tension of the fluid 

 must be nearly proportionate to the number of surfaces, imper- 

 fectly conducting, which are interposed between the ends of a piU 

 or battery, the density of the fluid becoming greater and greater 

 by a limited quantity at each step : and it is easily understood, 

 that any point of the pile may be rendered neutral, by a connec- 

 tion with the earth, while those parts, which are above or below 

 it, will still preserve their relations unaltered with respect to each 

 other: the opposite extremities being, like the opposite surface of 

 a charged jar, in contrary states, and a partial discharge being 

 produced, as often as they are connected by a conducting sub- 

 stance. The various forms in which the piles or troughs are con. 

 structed, are of little consequence to the theory of their operation: 

 the most convenient are the varnished troughs, in which plates of 

 silvered zinc are arranged side by side, with intervening spaces for 

 the reception of water, or of an acid. 



