Thermal Conductivity and Emissivity. 281 



found were as follows : — 



v /^=087. 



V Tj 



x v 



x 2 





20 mm. 



13 mm. 



•65 



40 



29 



•72 



60 



42 



•70 



85 



64 



•75 



110 



78 



•71 



Mean = -71 

 Similar experiments with copper rods gave : — 



^ = 3*35 mm., r 2 =2'45 mm. a /— =086. 



t ■* 





v n 



x\. 



x 2 . 



*2 



20 mm. 



18 mm. 



•90 



40 



25 



-Q2 



60 



34 



•57 



80 



47 



•59 



100 



61 



•61 



In the first value of — some error has, no doubt, crept in. 



Mean of last four = * 60. 

 Another set of experiments with the same rods gave : — 



x v 



.r 2 . 



-2. 



20 mm. 



10 mm. 



•50 



40 



22 



•55 



20 



11 



•55 



40 



22 



•55 



20 



12 



•60 



Mean = * 55 



To ascertain whether the copper rods really consisted of 

 the same metal, their specific electrical resistances were com- 

 pared. The result was 



& = '80. 



Pi 



Assuming that the ratio of thermal conductivities was the 

 same as that of electrical conductivities, this gives 





'11 



