﻿1146 Ionization of Abnormal Helium Atoms. 



electron-energy has a smaller value than this, some of the 

 abnormal atoms produced by absorption of radiation corre- 

 sponding to the final transitions at recombination cannot be 

 re-ionized, and hence the arc can no longer be maintained. 



In the experiments of Kannenstine, the re-striking of the 

 arc below 20'4 volts must have been due to the fact that 

 the interval which elapsed between the breaking of the arc^ 

 and the re-application of the energy necessary for the ioniza- 

 tion of abnormal atoms, was sufficiently short for there to be 

 still a considerable number of abnormal atoms present at the 

 end of the interval. This does not necessarily imply that 

 any particular abnormal atom remained in the abnormal 

 condition for the whole of this time, for the presence of 

 abnormal atoms at the end of the interval would be secured 

 if the radiation were absorbed and re-emitted by other atoms 

 several times during the interval. It does not follow, 

 therefore, that the period of *0024 second measured by 

 Kannenstine represents the "life" of individual abnormal 

 atoms. 



In the event of radiation being absorbed and re-emitted 

 several times during the interval, there would be, as we have 

 already shown, a marked falling off in the number of ab- 

 normal atoms corresponding to voltages greater than 21*2, 

 so that the abnormal atoms present at the end of the interval 

 would be almost entirely of the types corresponding to 

 20*4 volts and 21'2 volts, requiring between 4 and 5 volts 

 energy for their ionization. It thus appears that the main- 

 taining of the arc down to 4 or 5 volts and not below tins 

 value, and the fact that it re-strikes when this voltage is 

 again established, can be accounted for without assuming 

 the metastability of any abnormal state of the helium 

 atom. 



The authors desire to express their thanks to the Radio 

 Research Board of the Department of Scientific and In- 

 dustrial Research for the means of purchasing some of the 

 apparatus used in these experiments. 



Royal Holloway College, 



Englefield Green, Surrey. 



