762 Sir J. J, Thomson on the 



affected by temperature, and to diminish as the temperature 

 increases. 



Badeker (ZeitscJirift fur physik. Chemie, xxxvi. p. 305) 

 has determined the specific inductive capacity of many 

 gases at varying temperatures, and it appears from his 

 results that some of these, such for example as H 2 0, NH 3 , 

 S0 2 , HC1, CH3OH, &c, exhibit all these characteristics 3 

 they have high specific inductive capacities, K is very much 

 greater than n 2 , and K diminishes as the temperature in- 

 creases. 



As the specific inductive capacities afford perhaps the 

 most direct way of determining the moments of the electrical 

 doublets in a molecule, we shall proceed to find an expression 

 for the part of the specific inductive capacity due to these 

 moments, using the method employed by Langevin to 

 determine the variation with temperature of the magnetic 

 susceptibility of ferro-magnetic substances. 



Suppose that each molecule of a gas contains an electric 

 doublet whose moment is M, and that the gas is in a uniform 

 electric field, the electric force being X : when the axis of 

 the doublet makes an angle 6 with the direction of X, 

 the potential energy of the doublet in the field will be 

 — XM cos 6 : hence the number of molecules in unit volume 

 which have their axes inclined at an angle between 6 and 

 6 + B6 with the direction of the electric force, will be 

 equal to 



Ce sin 6 . av, 



where h is the constant occurring in Maxwell's law for the 

 distribution of velocities among the molecules of a gas, and 

 C a quantity which does not depend on 0. The moment 

 parallel to the electric force which these molecules con- 

 tribute is 



CM cos 0e sin 6 . dd : 



hence the total moment in the molecules parallel to the 

 electric force is equal to 



)s0e* XMco8<? S i n Odd 





AXM -AXM 



