into the Cause of Voltaic Electricity. 291 



heated even to redness in consequence of its resistance to the 

 passage of the current. But the reply is completely false when 

 the conductor is imperfect, such as a liquid or two points of 

 charcoal ; a rather considerable number of pairs must be made 

 of the surfaces in this case in order that the current may pass, 

 decompose, and heat the liquid, and produce heat and light 

 between the two points of charcoal. It is therefore exceed- 

 ingly inaccurate to distinguish the nature of effects by the 

 number of pairs most favourable for their production ; and 

 to say, for example, that to produce considerable calorific 

 effects, piles of large surfaces and a small number of pairs 

 must be employed, — and inversely, for considerable chemical 

 and physiological effects. Experiment has proved that the 

 degree of conductibility of the body interposed between the 

 poles, alone determines the number of pairs most favourable, 

 whatever be the nature of the effect produced, and that this 

 number is exactly in an inverse ratio to the conductibility of 

 the body. 



This law flows immediately from the theory of the pile 

 which we have enunciated. In fact, when the two electrici- 

 ties are accumulated at the two poles of the pile, they have, 

 as we have seen, two different ways of neutralizing each other, 

 that of the pile itself and that of the conductor, which unites 

 the two poles. The larger or smaller proportion of the two 

 electricities which follow either of these paths, depends upon 

 the relative facility afforded by them for their reunion ; if the 

 pile be in ever so small a degree a better conductor than the 

 body interposed between its poles, no portion of the current, 

 or only a very feeble one, will traverse this body. In every 

 case, therefore, the number of pairs formed from the given 

 metallic surfaces must be large enough to render the pile a 

 worse conductor than the body placed between its poles. 

 Care must also be taken to make all these pairs equal, for 

 should one of them be smaller than the others, its influence, 

 as we have already seen, immediately diminishes the quan- 

 tity of free electricity which circulates in a given time through 

 the conductor. This result is in exact agreement with my 

 own observations, and with some experiments very recently 

 performed by Mr. Binks, (Phil. Mag., July 1837,) which 

 confirm with the most remarkable precision the theory which 

 we have given. 



Examination of circumstances "which affect the power of the pile. 



We have supposed in the preceding paragraph that the 

 quantity of metal employed to make a pile is constant ; but 

 it may happen that in a given pile either the surface or the 



2 P2 



