798 Dr. G. Rudorf on the Molecular and 



From Lord Eayleigh's values of rj, and his own values of 12, 

 Meyer (l. c. p. 194) calculated for 



Helium, L = 2'40 x 10~ 5 cm., 

 and for Argon, L = 0*99 x 10" 5 cm. 

 From Schultze's values of rj Schmidt calculated for 



Helium, L = 2-857xl0" 5 cm., 

 and for Argon, L = 1*002 X 10 -5 cm. 



J. J. Thomson ('The Conduction of Electricity through 

 Oases/ 2nd edit. p. 450) calculated L for helium from 

 Lord Rayleigh's viscosity value and found 2 , 6xl0~ 5 cm., 

 but he does not give any further numerical details. 



The viscosities of neon, krypton, and xenon nave not been 

 determined. 



C. Molecular Diameters. 



The mean effective diameter of the molecule (cr) can be 

 calculated in a number of ways ; and it is of interest to see 

 whether the results thus obtained agree among themselves, 

 There are two general methods : — 



1. The method involving L ; and 



2. The method involving N. 



1. The method involving L. 



From the kinetic theory, we have the relation 



L = ,,. 1 ; 



and from this by multiplying through by a and rearranging 

 <r = 6*/2[~N<r 3 ]L. 



77" 



The quantity in the bracket, -~ ~Na 3 , is the volume occupied 



by the molecules themselves in unit gas volume, and if we 

 denote this by Y, we have 



<r = 6\/2YL (A) 



We can get at Y from 



(«) The density of the liquid as an upper limit; 



(6) The coefficient b of the van der Waals' equation ; 



(c) The dielectric constant ; and 



(d) The refractive index. 



