GALVANISM. 



pared the muscle of a living animal to a 

 Leyden phial, charged by the accumula- 

 tion of electricity on its surface ; while 

 he conceived that the nerve belonging 

 to it performed the function of the wire 

 communicating with the interior of the 

 phial, which would, of course, be charged 

 negatively. In this state, whenever a 

 communication was made, by means of 

 a substance of high conducting power, 

 between the surface of the muscle and 

 the nerve, the equilibrium would be in- 

 stantly restored, and a sudden contrac- 

 tion of the fibres would be the conse- 

 quence. 



(3.) The discoveries of Galvani were 

 no sooner made known to the scientific 

 world, than they excited very general 

 interest ; and philosophers in every 

 country in Europe vied with each other 

 in repeating his experiments, in varying 

 them in all possible ways, and in invent- 

 ing all kinds of hypotheses to account 

 for the phenomena. Some regarded 

 them as the effects of a new and un- 

 known agent, differing altogether from 

 electricity; while others, adopting the 

 views of Galvani, recognised them to be 

 electrical, but attributed them to a pe- 

 culiar modification of that power, re- 

 siding in the animal system only, and 

 which they accordingly distinguished by 

 the name of Animal Electricity. But 

 the discovery of new facts contributed 

 more and more to multiply and strengthen 

 the analogies between galvanism and 

 electricity: till at length all doubt of 

 the identity of the agent concerned in 

 all these phenomena was removed by 

 the discovery of the Galvanic, or Vol- 

 taic Pile. Whatever share accident 

 may have had in the original discovery 

 of Galvani, it is certain that the inven- 

 tion of the pile, an instrument which 

 has most materially contributed to the 

 extension of our knowledge in this 

 branch of physical science, was purely 

 the result of reasoning. Professor Volta, 

 of Pavia, a name already familiar to 

 electricians,* was led to the discovery of 

 its properties by deep meditation on the 

 developement of electricity at the sur- 

 face of contact of different metals. f 

 We may justly regard this discovery as 

 forming an important epoch in the his- 

 tory of galvanism : and indeed, since 

 that period, the terms, Voltaism, or 

 Voltaic Electricity, have often, in ho- 

 nour of this illustrious philosopher, been 



e on Electricity, 192, 193. 



used to designate that particular form 

 of electrical agency, which is the subject 

 of the present treatise. 



Previously to our entering into a de- 

 tailed exposition of the facts relating to 

 this science, and of the theories which 

 have been proposed for their explana- 

 tion, it will be necessary to direct our 

 attention to the nature -of those arrange- 

 ments of bodies, which are the sources 

 of galvanic power. 



CHAPTER II. 

 Simple Galvanic Circles. 



(4.) THE process usually adopted for ! 

 obtaining galvanic electricity is to inter- 

 pose between two plates of different 

 kinds of metal a fluid capable of exert- 

 ing some chemical action on one of the 

 plates, while it has no action, or at least 

 a different one, on the other plate : and 

 then to establish a communication be- 

 tween the plates at some other part, 

 either by their direct contact with one 

 another, or by the intervention of con- 

 ducting substances. Let us take, for 

 example, a plate of zinc, Z, and another 

 of copper, C, (fig. 1.) and immerse 

 Fig.l. 



them, to a certain depth only, in diluted 

 sulphuric acid, A, contained in a glass 

 vessel, keeping their lower edges at a 

 little distance from one another: then, 

 inclining them towards each other, let 

 us bring their upper edges, which are 

 out of the fluid, into contact, as repre- 

 sented in the figure. The arrangement 

 we have thus termed constitutes what 

 is called a galvanic circle, in its simplest 

 form, of which the three parts, or ele- 

 ments, are zinc, acid, and copper ; each 

 of these bodies being^ in contact with the 

 two others. Under these circumstances 

 it is found that a quantity of electricity 

 is set in motion ; a continued current of 

 electric fluid passing from the zinc to the 



