GALVANISM. 335 



conductor of the machine, the same effects on the organs of taste produced by 

 the metals ought to be ascribed to the same cause. 



However sufficient this analogy might seem to the understanding of Volta, 

 it was insufficient for the rigid canons of the logic of modern physics, and he 

 accordingly sought and obtained more direct and unequivocal proof of his hy- 

 pothesis. Two disks, one of copper and the other of Sine, were attached to 

 insulating handles, by means of which they were carefully brought into con- 

 tact, and suddenly separated without friction. They were then presented sev- 

 erally to a powerful condensing electroscope. The usual indications of elec- 

 tricity were obtained, and it was shown that this electricity was positive on the 

 zinc, and negative on the copper. By repeating the contact, and collecting 

 the electricity by means of the condenser, sparks were produced, and the dem- 

 onstration was complete. 



That the contact of dissimilar metals was followed by the evolution of elec- 

 tricity, could therefore no longer be doubted. It will, however, hereafter 

 appear that philosophers are not even yet agreed that the contact is the imme- 

 diate or the only cause of the disengagement of electricity in such cases. 

 Chemical agency is now known to be one of the sources of electricity ; and its 

 operation is so subtle, often so imperceptible, and generally so inevitable, when 

 heterogeneous molecules come into contact, that doubts have been entertained 

 whether, in every case where electricity seems to proceed from contact, it has 

 not really its origin in feeble and imperceptible chemical action. 



Although the complete development of this last-mentioned idea belongs to a 

 much more recent epoch in the progress of electrical discovery, yet the chemi- 

 cal origin of electricity did not altogether escape notice even at the period to 

 which we now refer. 



Of the numerous philosophers in every part of Europe who took part in the 

 discussions, and varied and repeated the experiments connected with these 

 questions, one of those to whom attention is more especially due was Fabroni, 

 who, in the year 1792,* two years after the discovery of Galvani, communi- 

 cated his researches to the Florentine Academy. In this paper is found the 

 first suggestion of the chemical origin of Galvanic electricity. 



Fabroni observes that in the mutual contact of heterogeneous metals there 

 is a reciprocal action which favors chemical change ; that to this action must 

 be ascribed many well-known phenomena, such as the more rapid oxydation 

 of certain metals when combined, or in mere contact with other metals. Ac- 

 cording to him, a metal, like all chemical reagents, has a tendency to combina- 

 tion with another metal when they are brought into contact ; that this effect is 

 only prevented by the superior force of cohesion which prevails among the 

 particles of each. This cohesive force will, however, be lessened in its en- 

 ergy by the antagonism of the attraction of the molecules of the two metals 

 toward each other, just in the same manner as it would be lessened by the 

 action of heat. Being thus lessened, its opposition to the tendency which the 

 particles of either metal have to combine with oxygen, taken either from the 

 atmosphere, or obtained from the decomposition of water, would be proportion- 

 ally diminished, and such oxydation would accordingly be promoted. In this 

 way Fabroni accounted for the tendency of certain alloys of metal to oxydation, 

 and for the well-known fact that iron nails, then used in attaching the copper 

 sheathing to vessels, were rendered so liable to rust by their contact with the 

 copper, that they became soon too small for the holes in which they were in- 

 serted. He supposed, therefore, that in the experiments of Galvani and Volta, 

 in which the convulsions of the limbs of animals were produced, a chemical 



* The date of the researches of thin philosopher is generally, but erroneously, assigned to the 

 year 1799. 



