352 



GALVANISM. 



on the practice of his profession. His favourite studies 

 were anatomy and physiology. He soon received 

 the appointment of professor of anatomy in the cele- 

 brated institute of his native city, and published an 

 interesting treatise on the Urinary vessels of birds. 

 Encouraged by the approbation with which this work 

 was received, he resolved on writing a complete phy- 

 siology of birds; but he afterwards confined himself to 

 an investigation of the organs of hearing. In these 

 pursuits, he was fortuitously led to the discovery of 

 several phenomena, which have led to a new branch 

 of science, called, from the discoverer, galvanism. 

 (q. v.) On a journey to Sinigaglia and Rimini, he 

 was so fortunate as to trace the cause of the electric 

 appearances which are observed in the torpedo, and 

 wrote a learned treatise on this subject. Simple in 

 his manners and wishes, and being naturally inclined 

 to melancholy, he avoided general society. The loss 

 of his beloved wife, in 1790, rendered him inconsola- 

 ble. As his conscience would not permit him, during 

 the revolution, to take the oath required of all public 

 officers, he was' deprived of his office. He retired 

 into the country, and died Dec. 4, 1798. In Rome 

 a medal has been struck with his effigy. 



GALVANISM. Although this agent is generally 

 believed to be identical witli electricity, yet its mode 

 of production, and the laws which it observes when in 

 action, are so far peculiar, that it is most advantage- 

 ously treated of by itself. Its name is derived from 

 Gaivani (q. v.), an Italian philosopher, who, in a 

 course of experiments on animal irritability, observed 

 the first striking phenomenon which led to its dis- 

 covery. The origin of galvanism is due to a trivial 

 circumstance. A physician of Bologna had, in 1790, 

 prescribed a dish of dressed frogs to a lady affected 

 with rheumatism in that city. Some of these animals, 

 which had been skinned by one of Galvani's domes- 

 tics, lay in a dish upon the table, when the accidental 

 discharging of an electric machine upon the table, 

 caused a strong contraction of the muscles of the 

 frogs, although they had not been touched by the 

 spark. Gaivani, in varying his experiments, found 

 that the same phenomena of muscular contraction 

 may be produced by interposing one or two plates of 

 metal between a muscle and a nerve, and he was led 

 to conclude, that the muscles of an animal are nega- 

 tively electrified and the nerves positively, and that 

 the effect of the metal is merely to restore the 

 equilibrium. The fallacy of this theory was fully 

 shown, about ten years after, in the year 1800, by 

 Volta, a celebrated professor of natural philosophy at 

 Pavia, who excited similar contractions by making a 

 connexion between two parts of a nerve, between 

 two muscles, or between two parts of the same 

 muscle ; but to produce the effect, two different metals 

 were found to be requisite. He showed also, that in 

 a similar way sensations can be excited ; as, for ex- 

 ample, a piece of silver being applied to one side of 

 the tongue, and a piece of copper to the other, when 

 their edges are brought into contact, or a connexion 

 is established between them by a conductor, a pecu- 

 liar taste is felt, and often a flash of light appears to 

 pass before the eyes. Hence he was led to infer, tliat 

 the electricity is derived, not from the living system, 

 but from the action excited between the metal and 

 the humid animal fibre ; that the animal matter acts 

 merely as a medium conducting this electricity, and 

 that the effects produced are to be ascribed to the 

 stimulus of the electric fluid passing along the nerves 

 and fibres, as in a shock from a Leyden jar. In the 

 further demonstration of his views of the production 

 of galvanism, Volta showed that plates of different 

 metals, such as silver and zinc, in contact with 

 one another, are excited, the silver negatively, and 

 the sine positively ; and, by employing several pairs 



of these plates, connecting them In such a manner 

 that the electricity excited by each pair should be 

 diffused through the whole, he discovered a mode of 

 greatly augmenting the galvanic energy, and pre- 

 sented to chemistry an unrivalled instrument of 

 research. It consisted of any number of pairs of 

 zinc and copper, or zinc and silver plates ; eacli pair 

 being separated from the adjoining ones by pieces of 

 cloth, nearly of the same size as the plates, and 

 moistened in a saturated solution of salt. The 

 relative position of the metals in each pair was the 

 same in the whole series; i. e., if the copper was 

 placed below the zinc in the first combination, the 

 same order was preserved in all the others. Thr 

 pile, the construction of which will be better under- 



n n n 



stood by the aid of the annexed 

 figure, was contained in & 

 proper frame, formed of glass 

 pillars, fixed into a piece of 

 thick wood, which afforded the 

 apparatus both support and in- 

 sulation. The instrument thus 

 arranged was found to be in the 

 same state of excitement as the 

 single pair of metallic plates, 

 affecting the electrometer, and 

 exciting muscular contractions, 

 in a similar manner, but in a 

 much greater degree. The 

 opposite ends of the pile were 

 also differently excited, the side 

 which began with a zinc plate being positive, and the 

 other negative ; and hence, when they were made to 

 communicate by means of a wire from each, electricity 

 flowed from one to the other in a continued current. 

 If the wires were applied to living matter, sensations 

 and contractions were excited : they also gave the 

 electric spark. This instrument, at present rarely 

 used, in consequence of more convenient arrangements 

 upon the same principle, has received the name of the 

 voltaic pile. Another apparatus for the same pur- 

 pose was invented by Volta, which he called the 

 couronne de tasses. It consisted of a series of glass 

 cups nearly filled with water or a saline solution. 

 In each cup was placed a plate of zinc, and a plate 

 of silver or copper ; the plate of silver in the one cup 

 being connected with that of zinc in the other, by a 

 thin slip of metal bent into an arc, and the same 

 order being preserved as in the construction of the 

 pile. Several improvements upon the voltaic pile 

 were soon made by other philosophers ; and the 

 discoveries in galvanism multiplied with a rapidity, 

 and to an extent, which surpass any thing before 

 known in the history of science. In attempting to 

 gave an outline of these discoveries, we shall observe 

 the following order : 1. The construction of the 

 galvanic apparatus, and the circumstances essential 

 to the excitement of this modification of electricity ; 2. 

 its electrical effects ; 3. its chemical agency ; and 4. 

 the theory of galvanism. 



1. The simple contact of different conducting bodies 

 is all that is necessary for the excitement of galvanic 

 electricity. Conductors of electricity (see Electricity) 

 have been divided into perfect and imperfect ; the for- 

 mer comprehending the metals, plumbago and char- 

 coal, the mineral acids, and saline solutions; the latter 

 including water, alcohol, and ether, sulphur, oils, 

 resins, metallic oxides, and compounds of chlorine. 

 The least complicated galvanic arrangement is termed 

 a simple galvanic circle. It consists of three con- 

 ductors ; of which one, at least, must be solid, the 

 second fluid ; the third may be either solid or fluid. In 

 the following tables, some different simple circles are 

 arranged in the order of their powers ; the most 

 energetic occupying the highest place. 



