332 GALVANISM. 



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^ ged, the positive electricity accumulated on the inner surface of the glass is 

 maintained there, in spite of the tendency it has to escape in virtue of its self- 

 expansive property, by the attraction of the negative electricity accumulated 

 on the external surface. When a communication is made between the inter- 

 nal and external surfaces by a metallic wire, this state of equilibrium ceases ; 

 the positive fluid of the inner surface runs along the wire in one direction, and 

 the negative fluid of the external surface runs along it in the other direction, 

 until each neutralizes the other, and a new state of equilibrium is established 

 by the actual combination of the two fluids. If this change occupied a sensi- 

 ble interval of time, and it were required to investigate the effects which would 

 be produced during that interval either on the jar and wire, or on any bodies 

 which might be within their influence, the question would properly belong to 

 ELECTRO-DYNAMICS ; but in fact the discharge, as it is called, or the transition 

 from the one state of equilibrium to the other, is instantaneous, and the same 

 may be said of all the phenomena which form the subject of the preceding 

 pages. 



In the commencement of this notice, the frequent influence of circumstances, 

 apparently fortuitous, on the progress of discovery in the sciences, has been 

 mentioned. It would be difficult, either in the history of the sciences or of the 

 political growth of states, to find a more signal example of this than was offered 

 by the discovery of that powerful instrument of physical investigation, the 

 VOLTAIC PILE. "It may be proved," says M. Arago, "that this immortal dis- 

 covery arose in the most immediate and direct manner from a slight cold with 

 which a Bolognese lady was attacked in 1790, for which her physician pre- 

 scribed the use of frog-broth." 



Galvani was professor of anatomy at Bologna. At the period just mentioned, 

 it happened that several frogs, divested of their skins, and prepared for cook- 

 ing the broth prescribed for Madame Galvani, lay upon a table in the laboratory 

 of the professor, near which at the moment stood an electrical machine. One 

 of the professor's assistants, being employed in some process in which the ma- 

 chine was necessary, took sparks occasionally from the conductor, when Mad- 

 ame Galvani was astonished to see the limbs of the dead frogs convulsed with 

 movements resembling vital action. She called the attention of her husband 

 to the fact, who repeated the experiment, and found the motions reproduced as 

 often as a spark was taken from the conductor. This was the first, but not the 

 only or chief part played by chance in this great discovery. 



Galvani was not familiar with electricity. Had he been so, he would have 

 seen in the convulsions of the frog evidence of nothing more than a high elec- 

 troscopic sensibility in the nerves of that animal, and an interesting example 

 of the known principle of electrical induction. But luckily for the progress of 

 science, he was more an anatomist than an electrician, and beheld with senti- 

 ments of unmixed wonder the manifestation of what he believed to be a new 

 principle in the animal economy, and, fired with the notion of bringing to light 

 the proximate cause of vitality, engaged with ardent enthusiasm in a course of 

 experiments on the effects of electricity on the animal system. It is rarely 

 that an example is found of the progress of science being favored by the igno- 

 rance of its professors. 



Chance now again came upon the stage. In the course of his researches he 

 had occasion to separate the legs, thighs, and lower part of the body of the 

 frog from the remainder, so as to lay bare the lumbar nerves. Having the 

 members of several frogs thus dissected, he passed copper hooks through part 

 of the dorsal column which remained above the junction of the thighs, for the 

 convenience of hanging them up till they might be required for the purposes of 

 experiment. In this manner he happened to suspend several upon the iron 



