GALVANISM. 



29 



law, that, independently of the effects of 

 chemical action, the influence of the 

 obstacle opposed to the passage of elec- 

 tricity from a fluid to a solid conductor, 

 is such, that when two metallic surfaces, 

 either of the same or of different metals, 

 are immersed in a fluid, so as to form a 

 galvanic circle, that metal which trans- 

 mits the electricity with the least loss of 

 intensity is positive with respect to the 

 other metal.* 



- (99.) The influence of this retarding 

 cause varies also with the intensity of 

 the current itself. The loss of electricity, 

 from its passage through a number of 

 metallic plates^ is scarcely sensible when 

 the current is very energetic, as, for in- 

 stance, when it proceeds from a battery 

 composed of a great nnmber of plates ; 

 but it becomes more and more percepti- 

 ble, according as the original intensity 

 of the current is less considerable. It 

 is also remarkable that the current is 

 disposed to pass more readily through 

 imperfect conductors, which present a 

 great degree of resistance, when it has 

 previously been made to traverse a great 

 number of metallic plates. This was 

 illustrated in two comparative experi- 

 ments, in the first of which a current, 

 originally of high intensity, was reduced, 

 by passing through a considerable num- 

 ber of plates, till it was equal in inten- 

 sity to one originally weaker, that had, 

 in the second experiment, passed through 

 a smaller number ; of the two currents, 

 thus apparently rendered equal in every 

 respect, it was nevertheless found that 

 the one which had previously passed 

 through the greater number of plates, 

 was thereby rendered capable of passing 

 through any succeeding plate with less 

 loss ot intensity than the other current. 

 The phenomena, he states, correspond 

 to those which would take place, if we 

 could imagine that there were two dis- 

 tinct kinds of electric current the one 

 capable of passing indiscriminately 

 through all sorts of conductors, good or 

 bad ; the other capable of passingthrough 

 good conductors alone. The passage of 

 the currents through successive plates 

 gradually effect the separation of these 

 two portions, the plates arresting the 

 one which cannot pass so readily through 

 bad conductors, and giving free passage 

 to the other portion. 



(100.) M. Dela Rive has applied this 

 theory to the explanation of the different 

 effects resulting from the increase of the 

 number of the plates. If the pile, he 



* Annales dc Chimie et de Physique, xxxvii. iW4. 



says, consist only of a small number of 

 plates, the electricity produced by it, not 

 having undergone the above process of 

 filtration, as it may be called, only one 

 part of it will be capable of passing 

 through an imperfect conductor, which 

 is presented to it, and the other part will 

 be arrested ; but if a good conductor be 

 presented, the whole of the electricity 

 finds a ready passage, and will produce 

 corresponding effects. Electricity of the 

 former kind only will be capable of pro- 

 ducing chemical decompositions, and of 

 passing through organized bodies ; but, 

 in the latter case, it will be adequate to 

 the production of all the calorific and 

 magnetic effects. These modifications 

 of electricity would, if this theoiy were 

 established, have a remarkable analogy 

 with those of light and of haat, under 

 circumstances somewhat parallel. 



(101.) It must be observed, however, 

 that one source of the diminution of 

 effect consequent on the multiplication 

 of surfaces, exists in the transfer of ele- 

 ments which takes place in the fluid from 

 galvanic action. This transfer, as is re- 

 marked by Sir H. Davy, in as far as it 

 has actually occasioned the deposit of a 

 positive element on the negative surface, 

 and vice versa, has an immediate in- 

 fluence in checking the further progress 

 of the galvanic action ; and arrests it 

 completely when it has proceeded to a 

 certain extent. Hence the powers of 

 batteries are found to diminish by the 

 continuance of their action, and ulti- 

 mately to cease. This change we have 

 already noticed in treating of the che- 

 mical actions of the simple galvanic cir- 

 cle. ($ 41.) 



(102.) It is obvious that the several 

 causes of retardation now stated render 

 it exceedingly difficult to determine, pre- 

 vious to actual experiment, the relative 

 powers of different batteries, composed 

 of different materials, and consisting of 

 different numbers of alternations of its 

 parts. 



(103.) It is not easy to understand 

 the manner in which the chemical ele- 

 ments of a body decomposed by gal- 

 vanism, are carried to their respective 

 stations in the voltaic circuit. Thus if 

 the influence of a powerful battery> be 

 transmitted through water, it will ope- 

 rate in decomposing that fluid, although 

 the wires which form the communica- 

 tion with the poles be at a consider- 

 able distance from each other. They 

 may even be placed in separate vessels, 

 provided the portions of water in which 



