of some Gas Molecules J or Electrons. 233 



of electrons given in column 4 of the table, were calculated 

 on the basis of equation (1), using values of K estimated in 

 the manner suggested above*. 



if the equation of electron mobility suggested by 

 Townsend f be accepted as correct it becomes evident 

 that one is not justified in computing n according to the 

 equation (1) ; for in Townsend's equation the velocity of 

 agitation of the electron among the gas molecules is not a 

 constant. Also, if from the view-point of this equation the 

 value of A' be computed from the results of the electron 

 mobility measurements in N 2 , a value of \' which is several 

 times greater than that estimated on the basis of kinetic 

 theory results. The uncertain quantities V and W may be 

 eliminated from the equation by substituting the value of 

 "VV/V obtained from the Townsend equation, 



•815 e\' 



300 K' = - 



mW 



in equation (1). In this equation e is the electronic charge, 

 m is the mass of the electron, and the factor 300 is put in to 

 reduce the mobilities to volts per cm. The equation (1) then 

 becomes 



5e -j 1,760/ _ ^760j [■ 



•815 ( 



T =e .... (4) 



The factor K' is then the only uncertain factor present in 

 the equation besides the n which is to be determined. In the 

 table of results the values of n computed on the basis of this 

 equation are given in column 2. 



The preparation and purification of air, N 2 , 2 , and H 2 , 

 used in the determinations has been reported elsewhere J. 

 The C0 2 was prepared through the action of HOI on pure 

 marble. It was passed through a tube packed with NaHC0 3 , 

 then over heated CuO, and heated, finely divided, Cu. From 

 there it passed through a drying train of CaCl 2 and *P 2 5 

 tubes into the chamber through a trap cooled to —20° C. 

 by frozen CC1 4 . Absorption tests made with CaCl 2 failed to 

 reveal the presence of any water-vapour. On absorbing the 

 00 2 in NaOH a residue of 1 c.c. of an inert gas was found 

 present in about 250 c.c. of the gas. Tests with alkaline 

 pyrogallol indicated that this residue was free from oxygen. 



* This changes the value of N for 2 to 3-6 xlO 3 instead of 50,000 

 given in the original paper. 



t J. S. Townsend, //. cc. 



% L. B. Loeb, Phys. Rev. xvii. No. 2, pp. 89-115 (Feb. 1921) ; Proc. 

 Nat. Acad. Sci. vii. No. I (Jan. 1921). 



