Contemporary Advances in Physics, XXV 

 High-Frequency Phenomena in Gases, Second Part 



By KARL K. DARROW 



This article on high-frequency phenomena in gases, a continuation of the 

 one which appeared in the preceding number of this Journal, is concerned 

 with the self-sustaining high-frequency discharges. First come the condi- 

 tions for establishment of the discharge, a spark or corona if the gas-pressure 

 is high, a glow if it is low; then, the laws of the glow-discharge when estab- 

 lished in rarefied gas, in tubes with internal or external electrodes. The 

 complexity of the situation is such that fundamental theory is almost power- 

 less as yet, the article thus consisting chiefly of descriptions of data and 

 statements of empirical laws. 



THE article preceding this one was devoted principally to the things 

 which are observed when a high-frequency electric field, generally 

 small in amplitude, is impressed upon a gas which by some other 

 agency is populated with electrons. The gas may be, for instance, 

 the vehicle of a self-sustaining direct-current glow-discharge, carrying 

 a steady current-flow between two electrodes maintained at a constant 

 potential-difference. It will then be rich with free electrons, and also 

 with positive ions. To a part of this host of mobile charged particles 

 circulating among neutral atoms, the high-frequency field is applied 

 by means of a second pair of electrodes. Or, the gas may be flooded 

 with free electrons supplied from a heated filament, and the high- 

 frequency force will act upon these. In all these cases of Part I, the 

 motions which the high-frequency field imposes on the corpuscles are 

 held accountable for the phenomena. Predictions may then be made, 

 out of our knowledge of- the behavior of free electrons wandering 

 through gases under constant fields ; and on the whole, the observations 

 agree with the predictions to an extent decidedly satisfactory, though 

 enough remains unexplained to encourage further study. 



Those phenomena of Part I are thus the high-frequency analogues 

 of what happens, when a weak constant electric field is applied across 

 a gas which is ionized or flooded with free electrons by some external 

 agent: X-rays or beta-rays or the electrons from a hot filament, for 

 example, or a stronger field simultaneously applied in a different 

 direction and maintaining a glow-discharge. Now if such a feeble 

 field be gradually increased in strength, these electrons themselves 

 take up the role of ionizing agents; the ionization due to the external 

 agent is "self-amplified," as I have elsewhere said. When the field 



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