78 Mr. H. H. Poole on Thermal Conducticitij and Specific 



conductivity with temperature, but differ from them by 

 about 20 per cent, in value. They differ entirely from the 

 later results of the first experiment on basalt which showed a 

 fall of conductivity with rise of temperature, and also from 

 all the granite results. Accordingly another method was 

 made use of to directly compare the conductivies of granite 

 and basalt, and ascertain whether there is any large variation 

 in their ratio with rise of temperature. These experiments, 

 which will be described later, fully confirmed the results just 



Specific Heat of Basalt. 



The method employed was the same as before. As the 

 central aperture was only slightly larger than the wire, no 

 correction for it was necessary. The results of one rising 

 and three falling temperature determinations are plotted in 

 fig. 8. The mean result for the specific heat is 



8 = 0-188 + 0-265 x 10- 3 6>-0-25 x l()- 6 5> 2 . 



Fi*. 8. 



This gives a value 0*202 at 55 c 0. Dr. Joly's value for 

 basalt between 10° and 100° is 0*19961, so that the agree- 

 ment here is quite satisfactory. 



6007: 1 



Experiments on the Relative Conductivities of Granite 

 and Basalt. 



The arrangement shown in fig. 9 w T as employed to com- 

 pare the conductivities of the two rocks. A is a disk-shaped 

 electric heater designed to generate heat uniformly over its 

 surface. B> and C are disks of granite, D and E disks of 

 basalt. The diameter of these disks was 6*5 cm., their 

 mean thickness, which was carefully measured, varied from 

 0*651 cm. to 0*715 cm., the granite disks being slightly 

 thicker than the basalt ones. F and G are stout copper 



