Conductivity of Metals with Temperature, 205 



t. k. 



-207 



25 -1975 



50 -189 



75 -182 



100 -177 



200 -171 



numbers which can be expressed with considerable accuracy 

 by the formula 



A=-207(l— -001440. 



9. The result of all this appears, then, to be that, as far as 



experiment has hitherto gone, the conductivity (both calori- 



metric and thermometric) of the metals copper and iron may 



be expressed with moderate correctness as a linear function of 



dk 

 the Centigrade temperature, with a negative value for -=-, or 



-=A-B*. 

 cp 



and that it may be expressed with a trifle more accuracy by 

 an inverse function of the temperature, 



k _ A 

 cp~ b + t' 



because this may be written very approximately, when b is 

 much bigger than t, 



b\ b + b 2 )' 



I will therefore assume that the variation of conductivity in 

 any metal for moderate ranges of temperature is expressed by 

 the equation 



*=fe w 



and that, since the variations of density and specific heat are 

 known, the law of variation of conductivity in different metals 

 is sufficiently discovered as soon as we have found the value 

 of the constant b for each metal. Our object then is to find a 

 mode of calculating b. 



On the Variation of 6 with Temperature. 



10. We have now to consider in what way the other factor 

 of the right-hand side of equation (3), namely 6, may be ex- 

 pressed as a function of the temperature. 



The magnificent researches of Dulong and Petit on this 



