ON ELECTRICITY IN MOTION. 523 



knowledge. The intensity of the electrical charge, and the chemical and 

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

 number of alternations 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 proportional to the number of surfaces, im- 

 perfectly conducting, which are interposed between the ends of a pile 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 connexion with the earth, while those 

 parts which are above it or below it, will still preserve their relations un- 

 altered 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 substance. 

 The various forms in which the piles or troughs are constructed, 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. (Plate XL. Fig. 557.) 



It is unquestionable that the torpedo, the gymnotus electricus, and some 

 other fishes, have organs appropriated to the excitation of electricity, and 

 that they have a power of communicating this electricity at pleasure to 

 conducting substances in their neighbourhood. These organs somewhat 

 resemble in their appearance the plates of the galvanic pile, although we 

 know nothing of the immediate arrangement, from which their electrical 

 properties are derived ; but the effect of the shock, which they produce, 

 resembles in all respects that of the weak charge of a very large battery. 

 It has also been shown by the experiments of Galvani, Volta, and Aldmi, 

 that the nerves and muscles of the human body possess some electrical 

 powers, although they are so much less concerned in the phenomena which 

 were at first attributed to them by Galvani, than he originally supposed, 

 that many philosophers have been inclined to consider the excitation of 

 electricity as always occasioned by the inanimate substances employed, and 

 the spasmodic contractions of the muscles as merely very delicate tests of 

 the influence of foreign electricity on the nerves. 



Such is the general outline of the principal experiments and conclusions 

 which the subject of galvanism afforded before Mr. Davy's* late ingenious 

 and interesting researches, which have thrown much light, not only on the 

 foundation of the whole of this class of phenomena, but also on the nature 

 of chemical actions and affinities in general. Mr. Davy is inclined to infer 

 from his experiments, that all the attractions, which are the causes of 

 chemical combinations, depend on the opposite natural electricities of the 



% Outlines of a view of Galvanism, Jour, of the Roy. Inst. i. 49. Also, Hi. Tr. 

 1807, p. 1 ; 1808, pp. 1, 333; 1809, p. 1. 



