416 Mr. H. Davies on some Applications of the 



specific inductive capacity. Mosotti and Exner * further 

 developed the idea with reference to the equivalent ex- 



n 2 — 1 

 pression -^ — ^, n being the refractive index which on 



Maxwell's theory is equal to \/ K. Proceeding from 

 Clausius's expression it is possible to obtain the value of the 

 ratio of the volume at the absolute zero of temperature to 

 the real volume of the molecules. Let V, Y , Yi, and Y c be 

 the absolute volume, the volume at the absolute zero of 

 temperature, the volume of the liquid at temperature T (abs.), 

 and the critical volume respectively, of a unit mass of a 

 substance. Further, let Y = k .Y. 



From the law of the rectilinear diameter of Mathias it has 

 been shown that for liquids sufficiently far removed from 

 their critical temperatures t 



Di-9D.(^) a) 



2D C 



= zf? ( ltt ) 



where a is the coefficient of expansion and is equal to 



2T C -T + 

 In obtaining the above result use was made of Guldberg's § 

 result that Do = 4D c . Using this in equation (1) it follows 

 that 



D < = 2*T C (2) 



The ratio of the volume at the absolute zero to the absolute 

 volume is given by V = ATV, and on substituting in (2) it 

 follows that 



^ — i- (3) 



V«"2aAT fl K) 



This must be equal to the expression given by Clausius, and 

 therefore 



k+2 ~ 2*ny l } 



whence 



^±- 2 - ] -k (5) 



* Wien. Ber. xci. p. 850 (1885). 



t Phil. Mag-. April 1912. 



\ Ibid. 



§ Guldberg, Chem. Centr.-JH. vol. ii. p. 1042 (1898). 



