Galvanic Pile, and Electromotive Forces. 505 



tube A all went in the same direction, while in tube B a suc- 

 ceeding current received from the commutator an opposite 

 direction to that of the immediately preceding one. In this 

 way no perceptible polarization was produced, in tube B, upon 

 the platinum wires. If the current of the series was not too 

 strong, no evolution of gas was observed in tube B ; but if its 

 intensity was very great, it is true that gas-evolution was 

 perceived in B, but this was always much inferior to that 

 which took place in tube A. The current produced the same 

 amount of chemical decomposition in both tubes ; but in tube 

 B the separated gases for the most part combined again to 

 form water, whereas in tube A no such recombination took 

 place. From this it follows that chemical decomposition must 

 have occasioned a greater cooling of the liquid in A than in 

 B. On the other hand, the galvanic heating occasioned by 

 the passage of the current must have been equal in the two 

 tubes, because the resistance and the current-intensity were 

 the same in both ; for the circumstance that the polar wires 

 in tube A were coated with a thin layer of gas could not ex- 

 ercise any sensible influence upon the resistance. In con- 

 sequence of this there was ground for supposing that the rise 

 of temperature in tube A would be less than in tube B ; but 

 the contrary was observed : the temperature rose much more 

 quickly in A than in B ; and this was still the case when the 

 tubes were exchanged or the experiment varied in other 

 respects. The difference between the two thermometers in- 

 creased with the current-intensity. To give an idea of the 

 amount of this difference, it may here be added that, in an 

 experiment in which six Bunsen elements were employed, 

 within five minutes the temperature rose in the tube B from 

 16° to 26°, in the tube A from 16° to 30°. The difference 

 therefore amounted in this case to 4°. 



The cause of the greater heat-development in tube A can- 

 not possibly be any other than this — that in that tube there 

 was an electromotive force which acted in the opposite direc- 

 tion to the current of the series, while the incessant altera- 

 tion of the currents prevented the rise of such a force in the 

 tube B. 



By the foregoing the theorem is proved: — that if a galvanic 

 current traverses an electromotor in the same direction as that 

 in which the electromotive force acts, a quantity of heat is 

 consumed which is proportional to the electromotive force 

 multiplied by the intensity of the current ; and that if the 

 current has a contrary direction, exactly as great a quantity 

 of heat is generated. 



The experimental trials which have been instituted respect- 

 ing the thermal phenomena in the hydroelectric piles have 



