74 Galvanism , from Galvani to O/im. 



disks in the pile will always be equal to the number of pairs of 

 metallic disks contained in it. If the pile is insulated, the 

 sum of the numbers indicating the states of all the disks must 

 be zero; but if the lowest disk is connected to earth, the 

 tension of this disk will be zero, and the numbers indicating the 

 states of all the other disks will be increased by the same 

 amount, their mutual differences remaining unchanged. 



The pile as a whole is thus similar to a Leyden jar ; 

 when the experimenter touches the uppermost and lowest 

 disks, he receives the shock of its discharge, the intensity being 

 proportional to the number of disks. 



The moist layers played no part in Volta's theory beyond 

 j. that of conductors.* It was soon found that when the moisture 

 is acidified, the pile is more efficient; but this was attributed 

 solely to the superior conducting power of acids. 



Yolta fully understood and explained the impossibility of 

 constructing a pile from disks of metal alone, without making 

 use of moist substances. As he showed in 1801, if disks of 

 various metals are placed in contact in any order, the extreme 

 metals will be in the same state as if they touched each other 

 directly without the intervention of the others ; so that the 

 whole is equivalent merely to a single pair. When the metals 

 are arranged in the order silver, copper, iron, tin, lead, zinc, 

 each of them becomes positive with respect to that which 

 precedes it, and negative with respect to that which follows it ; 

 but the moving force from the silver to the zinc is equal to the 

 sum of the moving forces of the metals comprehended between 

 them in the series. 



When a connexion was maintained for some time between 

 the extreme disks of a pile by the human body, sensations 

 were experienced which seemed to indicate a continuous activity 

 in the entire system. Yolta inferred that the electric current 

 persists during the whole time that communication by con- 



* Volta had inclined, in his earlier experiments on galvanism, to locate the seat 

 of power at the interfaces of the metals with the rnoist conductors. Cf. his letter 

 to Gren, Phil. Mag. iv (1799), p. 62. 



