802 



Dr. Gr. Rudorf on the Molecular and 



N = 2*76 x 10 19 , and pointed out that, if his theory be correct, 

 this value must be exact and not simply an approximation. 

 Quite recently this value has been confirmed by Rutherford 

 and Geiger (Proc. Roy. Soc. lxxxi. p. 162 (1908)) by 

 measuring the charge on an a. particle. They found 

 N--=2 # 72xl0 19 , and give reasons for considering the pre- 

 vious determinations of Thomson and Wilson too high. 



We will, in the present paper, take N = 2'75x 10 19 per 1 c.c, 

 which is probably correct to 1 per cent. 



We can now, as before, calculate <x from 



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

 (/>) The coefficient b of van der Waals' equation ; 

 (c) The dielectric constant ; 

 (c/) The refractive index. 



(a) From the density of the liquid. 



The following table gives the values of V for all the gases 

 except Neon, the density of which in the liquid state is 

 unknown. The determination of d for He is by Kamerlingh 

 Onnes (I. c), for Argon by Baly and Donnan (/. c), for Kr 

 and X by Ramsay and travers (Phil. Trans. I. c). The 

 values for the gaseous state (p) are those deduced above. 





p. 



d. 



v =^ 



Helium 



0-0001769 



000089 



0001782 



0-003709 



0-005842 



0-15 



9 



1-423 

 2155 

 3-52 



1-18X10- 3 



? 

 1-252x10-3 

 1-72X10 -3 

 166xl0~ 3 





Argon 



Krypton 













Taking N = 2*75 x 10 19 , we get the following values of a. 





He. 



Ne. 



A. 



Kr. 



X. 



orXlO cm. 



434 



? 



4-43 



493 



4-88 



The values for He and A are considerably smaller than 

 those obtained in the corresponding section above ; and it is 

 rather noteworthy that the cr-values for He, A, Kr, and X 

 are so little different from one another. 



