adduced by Prof. Faraday in support ofDe la Rive's T/ieo)y. 1 95 



suppose that such an operation must be made with the circuit 

 interrupted. 



When the force of an electromotor becomes weakened by 

 keeping the circuit complete for some time, we know that by 

 suspending the communication between the poles it recovers 

 by itself its primitive force, either entirely or in part, without 

 the liquid being agitated in the smallest degree*. In order to 

 estimate the true value which in the present question ought 

 to be attached to this experiment, it will be useful to know 

 how much of the strength is owing to the agitation of the li- 

 quid, and how much to the repose of the electromotor. 



For this purpose I procured forty plates of zinc, and as 

 many of copper ; I tried five pairs, one after the other, taken 

 at hazard, and all produced an equal deviation of the galvano- 

 meter ; all in similar circumstances electrized to an equal ten- 

 sion the electrometer furnished with a condenser. I made 

 these first trials to be certain that the other pairs also would 

 produce the same effects under similar circumstances, and 

 thus to be able to make use of new plates in every experi- 

 ment, in order the better to obtain the necessary similarity of 

 circumstances. 



I have made other preliminary experiments to ascertain 

 what force such pairs would lose when kept in action for a 

 given time, and how much of it they would regain by being 

 left in repose for a like given time. These things being pre- 

 mised, I came' to the examination of the experiment. 



II. I took therefore a plate of copper and one of zinc con- 

 nected by means of the wire of the galvanometer, and plunged 

 them two thirds of their height into the acidulated water. The 

 galvanometer deviated quickly full eighty degrees, but after 

 three minutes the deviation was only twenty-one degrees. 

 Having interrupted the circuit, and left it so for twenty mi- 

 nutes without agitating the liquid, the deviation which followed 

 on first re-completing it was thirty-two degrees, and it stopped 

 at last at twenty-one. After three minutes the needle was nearly 

 stationary at nineteen. I interrupted the circuit for twenty 

 seconds, and agitated the liquid, and then completing the cir- 

 cuit, the first deviation was of thirty- eight degrees, and when 

 the needle no longer vibrated it pointed to about twenty- 

 three. 



In another experiment I left the circuit closed during an 

 hour and five minutes. The needle of the galvanometer 

 pointed thirteen degrees; I opened the circuit, and after five 



• See Memoir upon the loss of tension, &c. in the /Innales de Chimic et 

 de Physique, August, 1828. 



02 



