Internal Pressure of a Liquid to its Dielectric Capacity. 113 

 experimentally. Further, since fjL = l + 4;7rk, it follows that 



oc= =£. The term ^777 can therefore not be zero, 



1 — fi^l 01 



provided Pascal's relation be true ; its value is, however, 

 extremely small. (It may be easily shown that if we no 



longer neglect the ^-r: term in the expression for ^7^, and 



ascribe the discrepancy — between Davies' expression and 



that obtained above for - ^- rp , — 'to the term thus introduced, 



7T O-l 



we are led to the impossible result that a is a negative 

 quantity. The discrepancy is therefore not due to the /j, 

 term.) 



Pascal's relation is of some importance from the stand- 

 point of the electron theory. The susceptibility k of a 

 diamagnetic substance is given by the expression (Campbell, 

 loc. cit. p. 123) 



n s^v 

 k= — 7 2 (electromagnetic units) ; 



where n is the number of revolving electrons per unit 

 volume, e the charge, and m the mass of an electron, r the 

 mean radius of the orbit of the electron (presumably the 

 vaiency electrons of Stark, which give rise to the electro- 

 magnetic field, and are the source of molecular attraction). 

 Pascal's relation may be stated, therefore, in the form 



nVeV 

 4y??oC 2 = a constant (r ), 



or nVr 2 = J> —- - =a constant. 



But nV represents the number of revolving electrons 

 present in unit mass of the substance, and if we regard this 

 as constant (independent of T and V but naturally dependent 

 upon the chemical nature of the substance) it follows that r, 

 the mean radius of the orbit of the revolving electron, is 

 constant for any given substance. Mow the recent work of 

 Bohr (Phil. Mag. July, Sept., Nov. 1913) and Conway (Phil. 

 Mag. Dec. 1913) has shown, in agreement with a suggestion 

 first made by Nicholson, that the angular momentum of a 

 revolving electron in an atom is a universal constant, either 



-or r) where h is the Planck constant. If the electron is 

 Phil. Mag. S. 6. Vol. 26. No. 1G3. July 1914. I 



