THE VOLTAIC PILE. 



219 



together electricity was developed, and by uniting a disc of copper and one 

 of zinc, and subjecting them to the test of an Electroscope, he found positive 

 and negative electricity developed in the zinc and copper respectively; so 

 Volta came to the conclusion that each metal parted with electricity, and 

 one became all " positive " and the other all " negative." But when he came 

 further to consider the possibility of building up a " pile " of these metal 

 discs sufficiently strong to produce electric effects, he found that if his theory 

 were correct he would lose from one side of the metal all he would gain 

 from the other, and therefore he could never obtain more than the slight 

 effect he had originally produced. 



This was at first a difficulty apparently impossible to remove. It was 

 so self-evident that the discs of metal, if placed in a pile in a series of pairs, 

 would continually exercise like effects to the first pair of discs, that Volta 

 was puzzled, and for some time he could not arrive at any reasonable solu- 

 tion. At last it struck him that if he placed between the discs some slow- 

 conducting substance, the electricity would not pass from disc to disc, and 

 the force developed or set in motion would be more powerful. 



He made the experiment. The result was 

 the Voltaic pile made in I 800, of which we give 

 an illustration (fig. 219). A communication on 

 the subject of Electricity by contact, written by 

 M. Volta, is to be found in the Philosophical 

 Proceedings for the year I 800. 



Volta constructed the pile which bears his 

 name, on the assumption that " every two 

 heterogeneous bodies form a galvanic circle. or 

 arc in which electricity is generated." The 

 "pile" consisted of a number of discs of zinc 

 and copper separated by discs of card soaked in 

 water. This combination of metals separated 

 by a bad conductor, developed considerable 

 electricity, the " positive " going to the zinc at 

 the top, and the " negative " turning to the 

 opposite end. By touching the zinc and copper 

 extremities simultaneously with wetted fingers 

 we shall experience a shock. " I don't need 

 your frog," Volta said, when he had proved his 

 theory ; " give me two metals and a moist rag, 

 and I will produce your animal electricity. Your frog is nothing but a 

 moist conductor, and in this respect it is inferior to my wet rag ! " 



After this discovery the theory of animal electricity died away for 

 many years, till in 1825, Nobili, and afterwards Matteucci, proved the exist- 

 ence of galvanic currents in muscles. 



After Volta had succeeded in obtaining a shock from his " pile," he 

 proceeded to the construction of another instrument, or rather apparatus, 



Fig. 219. -Voltaic Pile. 



