into the Cause of Voltaic Electricity. e 2S7 



city disengaged upon each pair of a pile is not mathematically 

 the same. The difference may arise from one of these three 

 causes: either that the pairs have not exactly equal sur- 

 faces, that the metals of which they are formed are not per- 

 fectly similar, or that the liquids in which they are immersed 

 are not completely identical ; circumstances which all have an 

 influence upon the total quantity of electricity produced in a 

 given time, and upon the portion of that electricity which re- 

 mains free. However, experience teaches, that when the two 

 poles of a pile are united by a conductor, the current which 

 traverses this conductor is still mathematically equal to that 

 which traverses each of the pairs of the pile. To establish 

 this important result, instead of soldering the zinc and copper 

 of the same pair to each other, an independent conductor must 

 be fixed to each. By means of these two conductors a me- 

 tallic communication is established between the two metals of 

 the pair, by the intervention of one of the wires of a double 

 galvanometer, the second wire of which serves as conductor 

 to the current of a second pair of the same pile, or to effect a 

 communication between the two poles. If these two currents 

 be carefully made to pass in contrary directions in each of the 

 wires of the galvanometer, their action upon the needle will 

 always be found absolutely null, provided they are mathema- 

 tically equal. This equality is easily explained. Take the 

 most feeble pair in the pile; let b be this pair; the positive 

 electricity disengaged by b cannot neutralize all the negative 

 of a ; there will remain then in the copper of a an excess of 

 negative electricity which will retain, by neutralizing it, an 

 equal quantity of positive ; the result will be that a, though 

 much stronger than b 9 can only set at liberty a quantity of 

 positive electricity equal to that of b. So also the negative 

 electricity of b can neutralize only a part of the positive of c; 

 the rest of this positive electricity will neutralize an equal part 

 of the negative of the same pair; and consequently c also can 

 only liberate a quantity of negative electricity equal to that of 

 b. It appears from this analysis, that the current of each pair, 

 and consequently the current of the whole pile, should be equal 

 to the current produced by the weakest pair. Now, experi- 

 ment fully proves, that if a feeble pair be introduced into a 

 pile composed of energetic pairs, the immediate result is a 

 considerable diminution in the force of the current of the pile, 

 and consequently of the current of each of the other pairs ; 

 but this reduction is never sufficient to render this current 

 equal to that which would be developed by the pair intro- 

 duced in an isolated state. Indeed, any pair whatever ne- 

 cessarily produces a greater quantity of electricity when it is 



