CHAMBERS'S INFORMATION FOR THE PEOPLE. 



Elementary Facts. Galvani, an Italian professor 

 of anatomy, discovered, about the year 1780, that 

 the limbs of recently skinned frogs were convulsed, 

 if near an electric machine, whenever he drew 

 sparks from the prime conductor. Experimenting 

 on this electric susceptibility of frogs, he acci- 

 dentally noticed one day a similar convulsion from 

 a totally different cause. This was when a copper 

 hook, stuck through the spine of a frog, came in 

 contact with a piece of iron which was touching 

 the muscles of the leg. The same action, though 

 less energetic, took place when he connected the 

 nerves of the back with the muscles of the leg by 

 a single metallic conductor. Galvani identified 

 the effect with that produced by the electric 

 machine ; and, after a great number of experi- 

 ments, he ultimately ascribed it to the flow of a 

 vital electric fluid from the nerves to the muscles. 

 One fluid he considered peculiar to the muscles, 

 and the other to the nerves. 



Volta, an Italian professor of natural philosophy, 

 repeated these experiments, but came to a different 

 conclusion. As the action was much more violent 

 when two metallic conductors were used, he in- 

 ferred that the mere contact of the different metals 

 was the exciting cause of the electric flow. One 

 of the metals assumed the positive, and the other 

 the negative electricity, and the frog's limbs but 

 served as a sensitive connector. Such was the 

 voltaic view. 



It was, however, a problem which of the ex- 

 planations was the true one. Each theory had its 

 advocates and supporting experiments, and each 

 party its name for the new species of electricity. 

 Thus came the origin of the two terms galvanism 

 and voltaic electricity, which are now used indif- 

 ferently. Volta's theory had perhaps most sup- 

 port at the time. Yet Galvani's is not without 

 reason, and may be said to be re-established by 

 modern experiments on animal electricity. 



In support of his theory, Volta devised many 

 ingenious experiments, and among others was a 

 simple apparatus, which excited extraordinary in- . 

 terest in its day. It is called Voltds pile, and was ! 

 invented by him to shew the effect of a combina- ' 

 tion of metallic contacts. It 

 consists of a number of pairs 

 of round discs of copper and 

 zinc piled together, as shewn 

 in fig. 1 8. The copper and 

 zinc of each pair were soldered 

 together, and the zincs all faced 

 the same way in the pile. 

 Moist discs of cloth were put 

 between each pair, merely, as 

 Volta held, to prevent direct 

 contact between the pairs, and 

 yet be a sufficient conductor. 

 The pile is insulated, and, as 

 afterwards modified, ends in a j 

 copper plate above and a zinc 

 plate below. By this means, a 

 powerful accumulation of posi- 

 tive electricity was found at the , 

 copper plate, and of negative at | 

 the zinc. When the two ends ! 

 of the pile were connected by a : 

 wire, a strong and steady flow of electricity set in 

 from the one side to the other. On the limbs of a 

 frog, the effect was much more violent than that 

 of a single pair of metallic conductors. So, then, 



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argued Volta, the mere contact of the copper and 

 the zinc produces opposite electricities in each. 

 For the more he multiplied the contacts, the 

 greater was the electrical power of the pile. 



Volta's theory took little account of the moisture 

 of the cloth, but its importance was not to be over- 

 looked. It was observed that, after a time, the 

 zinc plates got corroded by the action of the 

 moisture ; and, if the cloths were wetted with salt 

 water, a stronger electric action resulted, as well 

 as a faster corrosion of the zincs. 



Suspicion fell on this very corrosion as the real 

 active agent in the matter. The doctrine of 

 Volta was challenged by several eminent phil- 

 osophers ; and a theory tracing voltaic electricity 

 to chemical action was set up against it. By the 

 genius and labours of such men as Davy, De la 

 Rive, Becquerel, and Faraday, a vast array of 

 evidence has been brought to bear in favour of the 

 chemical theory. It has been shewn, on the one 

 hand, that in the experiments which were given 

 to demonstrate the contact theory, chemical action 

 is really at work, and that, if it be prevented, 

 no electricity appears. On the other hand, it is 

 proved that chemical action, or the union of two 

 substances having a chemical affinity or attrac- 

 tion, is always accompanied by the liberation of 

 electricity. 



To put such matters beyond dispute is ex- 

 tremely difficult. There are no theoretical reasons 

 why mere contact of dissimilar metals should not 

 give rise to a statical charge, or, in more modern 

 language, to a difference of electric potential in 

 the metals. Recent experiment seems to reassert 

 that mere contact does actually produce electricity, 

 and that Volta was perhaps not so far wrong after 

 all 



General Idea of Galvanic Action, It is in accord- 

 ance with the chemical view, that we proceed to 

 examine the conditions essential to the galvanic 

 current The 

 elementary form 

 of arrangement, 

 seen in fig. 19, / 

 is called a gal- 

 vanic element or 

 couple, and will 

 serve to explain 

 the nature of the 

 action. A plate 

 of copper, C, and 

 a plate of pure 

 zinc, Z, are put 

 into a vessel 

 of water, mixed 

 with a little sul- 

 phuric acid. So 

 long as they do 

 not touch, noth- 

 ing is seen, and 

 no chemical 

 action goes on. Fig. 19. 



But the moment 



they touch at any part, either within or out of 

 the liquid, bubbles of gas are seen at the copper 

 plate, and they continue to form till we sepa- 

 rate them again. We have the same result if 

 we connect the plates, not directly, but by wires 

 fastened to the plates. All that is visible is the 

 production of the gas bubbles. But a hidden and 

 most curious electric action is going on along the 



