ELECTRICITY IN MOTION. 3 



on the continent, to the mere mechanical actions of bodies pos- 

 sessed of different properties with regard to electricity. Thus, 

 they have supposed thut when a circulation of the electric fluid is 

 produced through a long series of substances in a certain direc. 

 tion, the differences of their attractions and of their conducting 

 powers, which must remain the same throughout the process, keep 

 up this perpetual motion, in defiance of the general laws of me, 

 chanical forces. In this country it has been generally maintained, 

 that no explanation founded on such principles could be admis. 

 sible, even if it were in all other respects sufficient and satisfac. 

 tory, which the mechanical theory of galvanism certainly is not. 



The phenomena of galvanism appear to be principally derived 

 from an inequality in the distribution of the electric fluid, origi- 

 nating from chemical changes, and maintained by means of the 

 resistance opposed to its motion, by a continued alteration of 

 substances of different kinds, which furnishes a much stronger 

 obstacle to its transmission than any of those substances alone 

 would have done. The substances employed must neither consist 

 wholly of solids nor of fluids, and they must be of three different 

 kinds, possessed of different powers of conducting electricity ; 

 but whether the difference of their conducting powers is of any 

 other consequence than as it accompanies different chemical pro. 

 perties, is hitherto undetermined. Of these three substances, two 

 must possess a power of acting mutually on each other, while the 

 other appears to serve principally for making a separate connexion 

 between them : and this action may be of two kinds, or perhaps 

 more ; the one is oxidation, or the combination of a metal or an 

 inflammable substance with a portion of oxygen derived from water 

 or from acid ; the other sulphuration, or a combination with the 

 sulphur contained in a solution of an alkaline sulphuret. 



We may represent the effects of all galvanic combinations, by 

 considering the oxidation as producing positive electricity in the 

 acting liquid, and the sulphuration as producing negative electri- 

 city, and by imagining that this electricity is always communicated 

 to the best conductor of the other substances concerned, so as to 

 produce a circulation in the direction thus determined. For ex- 

 ample, when two wires of zinc and silver, touching each other, 

 are separately immersed in an acid, the acid, becoming positively 

 electrical, imparts its electricity to the silver, and hence it flows 

 back into the zinc : when the ends of a piece of charcoal ar 



vor<. vr. D 



