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XL Short Electric Waves obtained by Valves. By E. W. 

 B. Gill, M.A., B.Sc, Fellow of Merton College, Oxford, 

 and J. H. Morrell, M.A., Magdalen College, Oxford *. 



1. f INHERE have recently been discovered methods for the 

 i generation of continuous oscillations of short wave 

 length (of the order of about a metre) by means of three 

 electrode valves. In January 1920, Barkhausen and Kurz f 

 found that with hard valves — i. e., valves at extremely low 

 pressure, if the filament and the plate were approximately 

 the same potential, or, indeed, if the plate were at a potential 

 considerably lower than the filament, provided that the grid 

 was kept at a high potential with regard to them, continuous 

 oscillations could be maintained in a circuit of the Lecher 

 Wire type connected to the grid and plate. The wave length 

 depended primarily on the grid voltage, but also on the 

 emission from the filament and on the plate voltage. 



Whiddington J had previously described another method 

 of getting oscillations of lower frequencies using a soft valve, 

 i. e.j a valve containing gas at low but appreciable pressure. 

 He employed more usual circuits for a valve, in that the 

 plate was at a high positive potential with regard to the 

 filament and the grid at a few volts above the filament. In 

 this case longer waves were emitted, and he noticed that if 

 V was the grid potential and \ the wave-length emitted, 

 then X 2 V was constant §. 



There appear to be other arrangements not hitherto re- 

 corded which will also give these waves. With a hard valve 

 and with the grid at a positive potential, oscillations can be. 

 obtained if the Lecher Wire system is connected across the 

 filament and grid.; the plate may be positive, negative, or at 

 the same potential as the filament, or it may be insulated. 

 Further, the third electrode — the plate — is unnecessary, for 

 oscillations can be sustained by means of a valve consisting 

 of a filament and an anode formed as a spiral of wire con- 

 centric with the filament, when these two are connected to 

 the Lecher wires. An intermediate arrangement has been 

 worked successfully in which the wave-length of the diode 

 connected as above is modified by a cylinder concentric with 



* Co mm uni cited by Prof. J. S. Townsend, F.R.S. 

 + Phifsikalischer ZeiUchriftj Jan. 1920. 

 X AY biddington, ' Radio Review,' Nov. 1919. 



§ For a general account of these experiments see ' Radio Review, 

 June 1920. 



Phil Mag. S. 6. Vol. 44. No. 259. July 1922. M 



