some other Constants of the Inactive Gases. 797 



B. Mean free 'paths. 

 The kinetic theory in its simplest form gives the following 

 relation between the viscosity coefficient 77, the density p, 

 the mean free path L, and the molecular velocity Gr : — 



?7=3 • pLGr, 



and this is equivalent to 



9? = 0-3614pLn. 



0. E. Meyer (I. c. p. 189), after introducing several cor- 

 recting factors involving complicated integrals, arrived finally 

 at the relation 



V = Q-30961 phtt, 



and this we will use for our calculations of L. The values 

 for p and 12 are given above, and we require, therefore, only 

 the values of the viscosity coefficients 77. These have been 

 determined for helium and argon only. 



Lord Rayleigh (Proc. Hoy. Soc. lix. p. 198 (1896)) found, 

 relatively to air = l, for 



Argon 1*21, and for 



Helium 0'9G. 



From these results, taking the absolute value of 

 Vo (air) = 0-000172, Meyer calculated 



Vo (Argon) =0-000208, 



t) (Helium) = 0-000165. 



Schultze (Ann. d. Phys. v. p. 140 (1901)) found for Argon 



i7 =0-0002104, 



and for Helium [Ann. d.Phys. vi. p. 302 (1901)) 



^0=0*0001891. 



This latter value is considerably higher than Lord 

 Rayleigh's, but it has been confirmed quite recently by 

 Schierloh, working with carefully purified gases. Prof. Dorn 

 kindly communicated these results to me ; I do not think 

 they have yet been published. Schierloh found for 



Helium, 77 = 0-0001887, and for 

 Argon, 77 = 0-0002114. 



Using these values of 77, we obtain for the mean free path L , 

 using the above formula, 



for Helium, L =2*85 x 10" 5 cm., 

 and for Argon, L = 1*006 X 10~ 5 cm. 



