The Motion of Electrons in Argon. 593 



discharge is less than or equal to that of the velocity of sound 

 through the gas under the discharge conditions which prevail. 

 For discharge pressures below this value, the assumption 

 (which is found to accord closely with experimental 

 fact) is made that the maximum discharge value holds 

 for all values of x. 



Other points worth noting are : — 



1. That the percentage error involved in the computation 



of discharges is three times the percentage error in 

 velocity computations on a constant specific heat 

 basis. 



2. That the discharge error increases as x decreases while 



the velocity error also increases: 



3. That the error in both velocity and discharge compu- 



tations on a constant specific heat basis increases as 

 the temperature of the gas in the reservoir is increased. 

 In other words, for a given reservoir pressure pi the 

 errors increase as the density of the gas in the 

 reservoir is diminished. 



The conclusions reached here with regard to the effect of 

 variable specific heat on gas discharges are somewhat like 

 those reached in a previous paper* by the writer on "The 

 Effect or Variable Specific Heat on Thermodynamic Cycle 

 Efficiencies.'" The equations deduced in that paper were of 

 analogous form to those given here for orifice discharges. 

 The applicability of the former to, and their value in, practi- 

 cal internal combustion work has since been fully demon- 

 strated, and it is hoped that equations (6) to (9) may prove 

 of equal value. 



LXX. The Motion of Electrons in Argon. By J. S. Townsend, 

 M.A., F.R.S., Wykeham Professor of Physics, Oxford, 

 and V. A. Bailey, M.A., Queens College, Oxford^. 



1. TN the December number of the Philosophical Magazine 

 JL we gave an account of the motion of electrons in 

 nitrogen, hydrogen, and oxygen, and it was shown that the 

 loss of energy of an electron in colliding with a molecule, 

 and the mean free path of the electron, may be found from 

 the experimental determinations of the velocity of the 

 electron in the direction of the electric force and its velocity 

 of agitation. We give in this paper the results of similar 



* Phil. Mag. Sept. 1917. 



t Communicated by the Authors. 



Phil. Mag. S. 5. Vol. 43. No. 255. March 1922. ' 2 Q 



