334 



Mr. S. Bid well on the Generation of 



in 30 seconds produced a deflection of 70 divisions, increasing 

 to a maximum of 131 divisions in 10 minutes. The current 

 then slowly diminished ; and in 5f hours after the commence- 

 ment of the experiment the deflection had fallen to 17 scale- 

 divisions. At this point the observations were discontinued. 

 In the accompanying curve the abscissas represent the time 

 in hours, and the ordinates the current in scale-divisions. The 

 current of 30 seconds' duration in the direction B A is not 

 represented. 



Hours. 



On another occasion, when the two Leclanche cells had 

 been connected for 3 minutes, the secondary current from B 

 to A decreased still more slowly than in the last-mentioned 

 experiment, vanishing in 3^ minutes. The current which 

 followed in the direction A B attained its maximum, indicated 

 by 155 divisions, in 6| minutes, and then steadily decreased 

 for nearly 4 hours, when it again became zero. The spot of 

 light did not, however, remain stationary, but moved steadily 

 on, indicating a second reversal of the current. In one hour 

 after zero had thus been crossed for the second time, the gal- 

 vanometer-deflection was 12 scale-divisions ; and 4^ hours 

 later, when the last observation was made, it had increased to 

 20 divisions. In both these experiments the galvanometer 

 (of which the resistance was nearly 3500 ohms) was shunted 

 with a coil of 100 ohms. 



These alternating currents are probably of the same nature 

 as those which Faraday found to be generated when copper and 

 silver, or two pieces of copper, or two pieces of silver, were 

 immersed in a solution of potassium sulphide*. The wires 

 are alternately protected from the action of the free sulphur 

 by an investing coat of sulphide. 



* Exp. Res. §§1911 and 2036. 



