Electricity through Argon and Helium. 299 



E.M.F. had to be added to the voltmeter circuit to bring the 

 readings within the range of its graduations. Larger E.M.F. 's 

 were added in this case than in the case o£ helium. They 

 were sufficiently large to be determined by the multicellular 

 itself. A key was employed which enabled either the added 

 E.M.F. or the added E.M.F. + the cathode-fall to be measured. 

 By subtraction the cathode-fall was found. 



The first set of satisfactory readings was as follows : — 



570, 570, 570, 572, 573, 572, 



571, 568, 570, 572. 



E.M.F. added 412 volts before readings, 



„ „ 412 „ after „ 



Mean value of cathode-fall 159. 



A second set of readings on the same sample of gas, made 

 next day, were as follows : — 



533, 533, 535, 528, 528, 

 528, 530, 528. 



Added E.M.F. measured before readings 370, 

 „ „ „ after „ 365. 



Mean value of cathode-fall 167 volts. 



A strong discharge from an induction-coil was now sent 

 through this sample of gas for a considerable time, with a 

 view to removing any traces of nitrogen that might remain 

 by absorption by the spluttered aluminium from the electrode, 

 as in the case of helium. 



The readings after this were :• — 



580, 581, 580, 584. 



E.M.F. added, measured before readings, 413, 

 „ „ „ after „ 413. 



Cathode-fall 168 volts. 



Another sample of argon was next tested. It is not necessary 

 to give the observations in detail, since they resemble closely 

 those given above. 



The mean results at first were : — 



171 volts. 



After prolongel sparking the cathode-fall remained almost 

 unaltered. The observed value was : — 



170 volts. 



