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Dr. H. H. Poole on the Electrical 



due to some small polarization effect which becomes less 

 important at higher temperatures, when the true conduction 

 current is much larger. 



The available range of gradients is much smaller than 

 with mica owing to the thickness of the specimen and also 

 to its small dielectric strength at high temperatures. The 

 specimen was pierced at 74° C. by a gradient of about 

 0*5 megavolt per centimetre, as shown by the point X on 

 the highest isotherm. As with mica oyer a similar range, 

 the isotherms are approximately right lines but they are not 

 parallel, the slope decreasing from 1*50 at 15° C. to 0*91 at 

 74° C. The conductivity is much larger than that of mica, 

 and the effect of temperature is also much greater, but the 

 general slope of the isotherms is very similar, the slope for 

 45° being nearly the same as the slope for mica. 



Par a fin Wax. 



Fig. 6 shows in section the arrangement used for testing 

 paraffin-wax. The heavily shaded parts represent the central 



Fiff. 6. 



metal rod, earthed metal guard-tube, and mercury pools on 

 either side of the wax film, which is shown stippled. The 

 diagonal dotted shading represents ebonite. The lower 

 mercury was first poured in and then sufficient paraffin-wax 

 was melted, in situ, to form a film of suitable thickness. 

 This was done by holding an iron plate ahove the w T ax and 



