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BELL SYSTEM TECHNICAL JOURNAL 



the large differences between the values of N, those of g show no 

 trend, which is as it should be. 



Another way of determining g without bothering about N has just 

 been carried into effect by Appleton and Chapman. Returning to 

 equation (7) : one readily sees that, if it be possible to vary g without 

 altering N, the conductivity should pass through a maximum when 

 g = mn. Now according to the simple interpretation the coefficient g, 

 being the measure of a sort of friction which the electrons suffer when 

 travelling through a gas, should increase with the pressure. If 

 therefore one can vary the pressure of the gas sufficiently while 

 applying the same high frequency, and maintaining the same degree 

 of ionization, one should find the conductivity passing through a 

 maximum. Moreover, anything proportional to the conductivity of 

 the gas should pass through a maximum, anything inversely pro- 

 portional to the conductivity should pass through a minimum. This 

 conveniently makes it unnecessary to measure the conductivity (or 

 anything else) absolutely; it is sufficient to choose something which 

 varies (say) inversely with conductivity, plot it as function of pressure, 

 and locate the minimum of the curve. For the pressure corresponding 

 to this minimum, the value of g is equal to the product of the mass 

 of the electron by the applied frequency. 



© 



s 



Pig_ 5 — Illustrating another scheme for estimating the dielectric constant and 

 conductivity of an ionized gas (in the tube between the plates K), with Lecher wires 

 and movable bridge P replacing the adjustable condenser of Fig. 1. (E. V. Appleton 

 & F. W. Chapman; Proc. Phys. Soc. London.) 



The apparatus and the circuit of Appleton and Chapman are shown 

 in Fig. 5; as one notices, the plates of the ionization-condenser are 

 now outside the tube and the ionized gas, and the high-frequency 

 circuit now comprises long parallel wires, known (after the man who 

 first used them as portions of high-frequency circuits) as Lecher wires. 

 The current through the galvanometer to the left (shunted by a 

 galena detector) is the measured quantity; the change which occurs 



