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CHAPTER I. 

 DISCOVERY OF VOLTAIC ELECTRICITY. 



WE have given the name of mechanico-chemi- 

 cal to the class of sciences now under our 

 consideration; for these sciences are concerned with 

 cases in which mechanical effects, that is, attrac- 

 tions and repulsions, are produced ; while the con- 

 ditions under which these effects occur, depend, as 

 we shall hereafter see, on chemical relations. In 

 that branch of these sciences which we have just 

 treated of, Magnetism, the mechanical phenomena 

 were obvious, but their connexion with chemical 

 causes was by no means apparent, and, indeed, has 

 not yet come under our notice. 



The subject to which we now proceed, Gal- 

 vanism, belongs to the same group, but, at first 

 sight, exhibits only the other, the chemical, portion 

 of the features of the class ; for the connexion of 

 galvanic phenomena with chemical action was soon 

 made out, but the mechanical effects which accom- 

 pany them were not examined till the examination 

 was required by a new train of discovery. It is 

 to be observed, that I do not include in the class 

 of mechanical effects the convulsive motions in the 

 limbs of animals which are occasioned by galvanic 

 action ; for these movements are produced, not by 

 attraction and repulsion, but by muscular irrita- 



