Cathode Fall in Hel'mni and Argon 



21 



at I mm. pressure, f/i, did not agree when computed from the two 

 pressures used. 



Two fresh filHngs of argon gave mobilities which checked quite 

 well and there was not any decided variation in the mobility when 

 the current density was changed. However, the mobility is about 

 five times as large as the value found by Franck with measure- 

 ments made at atmospheric pressure and increased by three or 

 four times its original value if the gas was allowed to stand in the 

 apparatus for several days. This makes it extremely doubtful 

 whether the value of mobility obtained is the value that would be 

 found if the argon were pure when the first measurements were 

 made. 



If the value found is larger than would be found for pure 

 argon, then this is a reliable method for measuring mobilities, and 

 Skinner's suggestion that in the case of hydrogen the high mobility 

 which he found — about twelve times as high as the values which 

 ordinary methods of measurements give — is due to an atomic ion 

 would be supported. This can be determined only by using pure 

 argon, which the writer was unable to secure for the purpose of 

 the present investigation, but hopes to be able to obtain for later 

 work. 



However, if the pure monatomic gases give abnormally high 

 mobilities, it seems probable that the form in which the mobility 

 factor enters the theoretical formula must need be modified, pre- 

 sumably bv the introduction of another constant factor. 



