IM.Ml IIM.h To I'lrtipITK HISCHAIMSK THROUGH VARIOUS GASES. 



It will l)e seen that the minimum was about 276 volts much lower than the 

 \ Allies obtained with nitrogen not specially treated. 



The treatment with the alloy was now continued for some hours. 

 The following set of readings was obtained after this : 



Further treatment with the alloy did not appreciably reduce the minimum 

 voltage. 



A repetition of this experiment with a fresh sample of nitrogen gave a result in 

 close agreement with the above. The minimum may be therefore taken as 251 volts. 



It will be seen that the perfect removal of oxygen does not much affect the slope of 

 tli<> curve in its straight part, where the pressure is above the critical value. The 

 interpretation of this (on the view given above) is that the cathode fall of potential, 

 not that near the anode, is affected by the presence of traces of oxygen. 



Helium. 



It lias len shown by Professor RAMSAY and Dr. COLUE (' Roy. Soc. Proc.,' vol. 59, 

 p. 259) that helium at atmospheric pressure allows sparks to pass through it much 



