48 Mr. IT. IT. Poole on the Thermal Conductivity 



Tli^ arrangement of the rock and Furnace is shown in 

 section in fig. 2. A is the rock cylinder. The circular grooves 



carrying the multiple couple for measuring the temperature 

 difference are shown in section, also the single uroove carrying 

 the single con pie. B is acopper tube 30*5 cm. long, 8*3 cm. 

 internal diameter, and about 1*6 nun. thick. The annular -pace 

 between A and B is filled with line carborundum powder. 

 The object of using a copper tube is to ensure that the whole 

 furnace shall at lain as uniform a temperature as possible. To 

 lessen oxidation at high temperature the tube was coated both 



inside and outside with blaeklead. The furnace winding 



(not shown in the figure) IS of nickel wire 2 mm. diameter 

 Uniformly wound in a single layer on the eopper cylinder, 

 hut insulated from ii by asbestos millboard. The BUCCeSsive 



turns of bare nickel wire are prevented Erom touching by a 



thin wire with a thick asbestos insulation. This thin wire 

 carries no current, and might be replaced by asbestos cord. 



