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BELL SYSTEM TECHNICAL JOURNAL 



composed of a source E of electromotive force; wires leading (one of 

 them through a galvanometer G) from the opposite poles of the 

 source to electrodes A and C; and a gas between the electrodes. For 

 convenience let us imagine the gas enclosed in a cylindrical vertical 

 tube, the electrodes near its ends. 



Take up first the direct-current discharge; say the cathode is above; 

 consider any surface, S, cutting across the gas which the tube encloses. 

 After the steady state is established, there will be positive ions 

 crossing the surface on their way toward the cathode (upward) 







E /Oo* 



Fig. 1 — Illustrating an internal-electrode tube for the transmission 

 of high-frequency current through gas. 



and negative ions crossing it on their way toward the anode (down- 

 ward). We may speak of these, both classes, as ions going in 

 the "right" direction. The total charge which they carry, as many 

 of them as cross in unit time, will be the current across the surface 

 — if there are no ions going in the "wrong" directions. But in 

 a luminous discharge there are generally positive ions crossing toward 

 the anode and negative ions crossing toward the cathode. The sum 

 of the charges which they carry must be subtracted from the former 

 sum; or, to express the idea better, they must be added with a 



