

Chemistry and Physics. 407 



pared at the Mint of Paris, in ihe laboratory of M. Pelouze and M. 

 Peligot. The needle, when set free, took about half a minute in mov- 

 ing from 50° to zero. 



was not at first acquainted with M. Reymond's method of proceed- 

 ing. In my earliest experiments, two cylindrical conductors were held 

 in the hands, and when the needle had returned to zero, or had acquired 

 a perfectly stationary position, one of the arms was powerfully con- 

 tracted ; the deflection was then observed, and when the needle had 

 again become stationary after the cessation of the contraction, the other 

 arm was strongly contracted, also observing the deflection. 



These first experiments were made with common copper conductors. 

 But for the sake of avoiding the objection which might arise from the 

 ready oxydation of this metal, I had them covered with gold-leaf. 

 Other conductors were coated with silver, platinum and gold. 



The experiments were made by three persons. Were there no oc- 



casion for using galvanometers, we should be inclined to believe thaU. 

 silver, and especially gold and platinum, which preserve their polish 

 and lustre in contact with moist air, would be appropriate for these ex- 

 periments, on account of their unalterability. This is however not the 

 case; silver, gold and platinum afford currents which are almost as 

 strong as copper. When the platinum conductor is held in the hand, 

 and the needle has become stationary, merely touching it with one fin- 

 ger more, or less, is sufficient to change the position of the needle sev- 

 eral degrees. 



In these experiments the needle was deflected 50°, 75° and even 90°. 

 When one of the conductors was squeezed powerfully, the needle 

 moved in one direction, and when the other conductor was squeezed, 

 the needle moved in the same or in an opposite direction. 



It is indispensable to repeat these experiments several times, without 

 which we should be liable to errors. Thus it happens that the deflec- 

 tions of the needle occur alternately in one and the other direction ; 

 but on multiplying the experiments, we find that the deflections fre- 

 quently take place in the same direction, although the compression is 

 produced first by one and then by the other arm. If the chemical ac- 

 tion was regular like that of a watch-spring, we ought to obtain cur- 

 rents in the opposite direction. We only experimented in this way, be- 

 cause, on the one hand, we were unacquainted with M. Reymond's 

 method of proceeding; and on the other, we thought that silver, and 

 especially gold and platinum, when simply held in the hand without any 

 compression, would only afford a very weak current. But experience 

 unfortunately proves that gold and platinum are under these circum- 

 stances as impressionable as brass, if I may be allowed to use such an 

 expression. I have repeated M. Reymond's experiment several times, 

 both following rigidly and varying his method of proceeding. 



I first wished to ascertain whether the instrument, which I had not 

 yet used, was sensible or not to changes of temperature. For this pur- 

 P°*e, I heated one of the places at which it was soldered to the melting- 

 point of wax, the communication being established by the hands be- 

 tween the two plates ; I also augmented the temperature of one of the 

 two solutions of common salt, by immersing in it glass tubes filled with 

 boiling water, the communication being always kept up by the hands; 





