226 



ELEMENTARY LESSONS ON [CHAP, iv, 



became much greater at those temperatures at which it 

 begins to conduct electricity. Boltzmann has announced 

 that in the case of two crystalline substances, Iceland 

 spar and sulphur, the inductive capacity is different in 

 different directions, according to their position with 

 respect to the axes of crystallisation. 



271. Specific Inductive Capacity of Liquids 

 and Gases. The inductive capacity of liquids also 

 has specific values. The following table is taken from 

 the data of Silow and of Gordon : 



Turpentine . 

 Petroleum . 

 Bisulphide of Carbon 



2-16 



2-03 to 2*07 

 1-81 



Faraday examined the inductive capacity of several 

 gases by means of his apparatus (Fig. 103), one of the 

 condensers being rilled with air, the other with the gas 

 which was let in through the tap below the sphere after 

 exhaustion by an air pump. The method was too rough, 

 however, to enable him to detect any difference between 

 them, although many experiments were made with dif- 

 ferent pairs of gases at different temperatures and under 

 varying pressures. More recently Boltzmann, and inde- 

 pendently Ayrton and Perry, have measured the specific 

 inductive capacities of different gases by very exact 

 methods ; and their results agree very fairly. 



272. Mechanical Effects of Dielectric Stress. 

 That different insulating substances have specific 



