Dielectrics in a Steady Field of Force. 403 



The ratio of Curie's values for quartz _L and II is 240 ; 

 those now obtained give 130. It is interesting to note that 

 the velocity of light in quartz is greatest when the wave- 

 front and current are in the direction of least electrical con- 

 ductivity. In accordance with previous ' observations the 

 lighter flint-glass has the higher resistivity. Paraffin- wax 

 was the most perfect insulator examined. 



Table II. 

 Specific Resistance of Dielectrics at 17° C. 



Substance. 



dK/dt. 



P 



ohms per 

 cm. cub. 





ilemp. 



Paraffin- Wax 



Quartz JL 



•00026 



•00064 



•00131 



•00163 



•00197 



•00805 



•0089 



•0316 



•059 



•077 



•097 



•107 



•35 



4-9 xlO 16 

 20 xlO 1 ^ 

 9-9 X10 1 ' 5 

 82 xlO^ 

 70 XlO 10 

 16 XlO 15 

 1-5 XlO 15 

 45 X10 U 

 2-8 XlO 14 

 25 xlO 14 

 1-55 XlO 14 

 1-53 X10 U 

 621 xlO 13 



1*3 

 34 X 10 Ayrton and Perry. 



•91 X 10 1 Curie. 



C.10X10 15 Threlfall. 



3-8 XlO 11 Exner. 



I'd X 10 Electrician. 



2'8xl6 Ayrton and Perry. 



•38x10 Curie. 

 4-5 XlO 14 Lat. Clark. 

 2-5 XlO 1 ' 3 F. Jenkin. 



j 46 



i 



46 



Flint-Glass A 33... 

 Sulphur 



Resin 



Fused Quartz 



Indiarubber 



Ebonite 



Canada Balsam 



Flint-Glass A 41 ... 

 Amber 



Quartz |J 



Gutta-percha 



It follows from equation (5) that when the period has 

 reached a steady state the apparent resistance of the dielectric 

 is infinite. This does not mean that no purrent could pass 

 through it if it were in contact with the poles but that the 

 polarization has reached its limit. 



Although the dielectric constant increases at a uniform 

 rate the apparent resistance increases also, as calculated 

 below, from the curves of fig. 2. This indicates that, as one 

 would expect, the mutual attraction of charges on adjacent 

 molecules increases in intensity as they approach, so that 

 though the resistance to movement increases, the rate, on the 

 whole, is maintained uniform. 



2 D 2 



