Voltaic Batteries, SjC* 277 



1, 2, and 4 inches above, we obtain this influence in the same 

 amount, but find it to be distributed over spaces progressively 

 increasing with the distance. 



161. Or the inference to be drawn from these facts may be 

 otherwise expressed ; that the amount of electrical action oc- 

 curring in such arrangements as those here employed, may be 

 condensed within a smaller space, or diffused over a larger 

 one, under certain limitations in both cases, in proportion as 

 the elementary conducting plate is approached to, or removed 

 from, the zinc or generating point, pi'esenting in these opera- 

 tions a marked analogy to the general phaenomena of the ra- 

 diation of light and heat. 



162. But in this kind of reasoning there are two assump' 

 lions; first, that the zinc is the point from which this influ- 

 ence emanates; and second, that the mass of liquid interposed 

 between the two plates is placed in any peculiar condition ; 

 and for neither of these have we the support of any direct evi- 

 dence. 



163. Light and heat radiate in all directions from any ge- 

 nerating point, as from one common centre. It matters not 

 to the present purpose by what theory we explain the mode 

 of emanation, or whether we assume their materiality or the 

 contrary. We know of their presence at any given distance 

 from the point of emanation, only by the interposition (as in 

 the case of light), of any body capable of receiving its impres- 

 sions, or of reflecting it; and in the case of heat, in like man- 

 ner, only by the agency of some body interposed, and capable 

 of appreciating or indicating its existence within the medium 

 through which it is supposed to be diffused or propelled. The 

 same agencies which serve to detect the presence of light and 

 heat, serve also to measure their quantities. And in like man- 

 ner does the copper-plate, in such voltaic arrangements as 

 the above, serve to indicate the existence of voltaic action, 

 and to measure its amount. The copper-plate may then be 

 considered as subserving the same purpose in electrical ex- 

 periments, as the screen in optical experiments, and the ther- 

 mometer in those of heat ; but with this (though perhaps only 

 apparent) difference, that the copper-plate is essential equally 

 to the production as to the measurement of electricity ; whereas 

 in the other two, their production is apparently independent 

 of the instruments by which their quantities are determined. 

 But making no attempt to trace the existence of any analogy 

 as regards the way in which these several agents are originally 

 produced, there seems, so far, to be some evidence for belie- 

 ving, that when once produced, some of the phaenomena they 

 exhibit are similar in general character ; and as far as regards 



