234 



GALVANISM. 



Volta. professor of natural philosophy at Como, and subsequently at Pavia, 

 had been already known for his researches in different parts of physics, but 

 more especially in electricity. The Bolognese experiments naturally engaged 

 his attention) and it was not long before his superior sagacity enabled him to 

 perceive that the theory of Galvani was destitute of any sound foundation, 

 j ndeed, a single experiment was sufficient to overturn it, though not to carry 

 conviction of its futility to the minds of its partisans. Volta applied the met- 

 als in contact with each other to the muscle alone, without touching the nerves, 

 and the convulsions nevertheless ensued. The analogy of the muscle and 

 nerve to the Leyden phial was no longer tenable. Volta transferred this anal- 

 ogy to the two metals, and contended that the mutual contact of two dissimilar 

 metals must be regarded as the source of the electricity ; that by the contact 

 the natural electricity was decomposed, and the positive fluid passed to one 

 metal, and the negative one to the other ; and that the muscle merely played 

 the part of a conductor in carrying off one of the fluids thus developed. 



To this Galvani replied by showing that, when a single metal was used to 

 connect the nerves and muscles the convulsions ensued, and that therefore the 

 contact of dissimilar metals could not be the source of the electricity. Volta 

 rejoined, that it was impossible to be assured of the perfect homogeneity of the 

 metal, and that any the least heterogeneous matter contained in it would be 

 sufficient for^his hypothesis. Also, that when a single metal was used, the 

 convulsions were uncertain, and never produced, except in cases where the 

 organs were in the highest state of excitability ; whereas, on the contrary, they 

 happened invariably, and were long continued, when the connexion was made 

 by two dissimilar metals. 



Tenacious of this cherished theory to the last, Doctor Valli, a partisan of 

 Galvani, confounded the advocates of the school of Pavia, by showing that, by 

 merely bringing the muscles themselves into contact with the nerves, without 

 the intervention of any metal whatever, the convulsions ensued. To this the 

 expiring effort of the Bolognese party Volta readily and triumphantly replied, 

 that the success of the experiments of Valli required two conditions : first, that 

 the parts of the animal brought into contact should be as heterogeneous as pos- 

 sible ; and, secondly, the interposition of a third substance between these 

 organs. This, so far from overturning the theory of Volta, only gave it in- 

 creased generality, showing, as it did, that electricity was developed, not alone 

 by the contact of two dissimilar metals, but also by the contact of dissimilar 

 substances not metallic. 



From this time, the partisans of animal electricity gradually diminished, and 

 no effort worth recording to revive Galvani's theory was made. Meanwhile, 

 the hypothesis of Volta was, as yet, regarded only as the conjecture of a pow- 

 erful and sagacious mind, requiring nevertheless much more cogent and direct 

 experimental verification. This experimental proof he soon supplied. 



The first analogy which Volta produced in support of his theory of contact 

 was derived from the well-known experiment of Sulzer. If two pieces of dis- 

 similar metal, such as lead and silver, be placed one above and the other below 

 the tongue, no particular effect will be perceived so long as they are not in 

 contact with each other ; but if their outer edges be brought to touch each 

 other, a peculiar taste will be felt. If the metals be applied in one order, the 

 taste will be acidulous ; if the order be inverted, it will be alkaline. Now, if the 

 tongue be applied to the conductor of a common electrical machine, an acidu- 

 lous or alkaline taste will be pe "ceived, according as the conductor is electri- 

 fied positively or negatively. \ olta contended, therefore, that the identity of 

 the cause should be inferred from the identity of the effects ; that, as positive 

 electricity produced an acid savor, and negative electricity an alkaline, on the 



