118 BELL SYSTEM TECHNICAL JOURNAL 



constant gradient in the positive column of the direct-current dis- 

 charge? A discharge of the latter type was set up in tubes (equipped 

 with internal electrodes, of course) which had been employed for the 

 high-frequency glow; the gradient in its positive column, measured by 

 Townsend and Nethercot with nitrogen and by Johnson with neon, 

 agreed fairly well with the value of Ihlir which is the mean value of 

 the gradient in the discharge taken over any half-cycle. As for the 

 term {V — hi), which has been interpreted as the sum of potential- 

 drops localized near the electrodes, it seems to vary inversely as the 

 frequency over the limited ranges aforesaid. 



To anyone desirous of penetrating through phenomena to funda- 

 mental laws, the situation as presented in this article must seem de- 

 plorable. The laws of the high-frequency discharge are almost purely 

 empirical, either unexplained altogether, or explained only in a vague 

 and qualitative way. Even the data do not form a complete or coher- 

 ent system. For the remaining type of high-frequency glow not 

 treated here — the so-called electrodeless discharge, in which high- 

 frequency magnetic as well as electric fields pervade the ionized and 

 excited gas — the situation is yet more obscure. Still, if the reader will 

 consult again the article which preceded this one, he will be reminded 

 that considerable progress has been made already in interpreting by 

 fundamental theory the events which happen, when high-frequency 

 fields are applied to gas which is independently ionized by other agents; 

 and this gives hope of future success in extending the theory to the phe- 

 nomena which occur when the high-frequency fields are themselves the 



causes of the ionization. 



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