Standard Tension- Galvanometer. 29 



amined with the standard galvanometer, gave rise to a study 

 of some little interest, though the arrangement of the standard 

 is not specially suitable for the purpose. 



The cells in question are made up with sulphate of zinc and 

 sulphate of copper, and the porous cells are rather thick. 



When first made up, the tension between the poles was 



5*66 volts; 

 after some hours, 6* 6 „ 



next morning, 7- 6 „ 



rose during the day to nearly 8 „ 



Then fell off, and for a day or two remained pretty constant 

 at about 6' 6 volts. 



I now determined the resistance by Mance's method, and 

 the result was very singular. The resistance was variable, 

 increasing when the current flowed, from a minimum of a 

 little less than 110 ohms to 250 and more. It required very 

 quick action after making contact to test the resistance while 

 below 110 ohms. 



I timed the change after the battery had rested some hours. 

 It took 25 minutes for the resistance to rise to 200 ohms, and 

 12 minutes more to reach 250. I then left the battery in 

 action for two days, to see what the ultimate condition would 

 be. The whole thing had then altered. 



Although the current had been flowing all the time, the 

 resistance had diminished again, and was now about 95 ohms. 

 It was apparently quite free from alteration. 



The following observations were made on successive days 

 after the change. The E.M.F. had risen considerably. It 

 appears probable that the sulphate of copper had penetrated 

 into the zinc cell. 



Tension between 

 poles. 

 Volts. 



Resistance. 



Total 



Tension per 



Ohms. 



tension. 



cell. 



95 



10-37 



1-152 



70 



10-16 



1-129 



50- + 



10-00 



1-111 



First day 9'60 



Second day ... 9*60 

 Third day 9'50 



The resistance had now become changeable again. It was 

 less than 50 ohms when contact was first made, but increased 

 and soon became greater. 



If we admit the Cambridge reduction of the B.A. unit to 

 ohms, accepting the factor '987, the final numbers become 

 somewhat reduced, the middle one becoming 1*1 14 volt per 

 cell nearly. 



This last condition of the cells, after the sudden rise of 



