270 



THERMOELECTRIC CURRENTS. 



The thermoelectrical power of two metals A and B at a temperature 

 t is equal to the difference of the thermoelectrical powers of the same 

 metals A and B in reference to any third metal C. 



For the law of intermediate metals gives the equation 



E(AC) = E(AB) + E(BC). 

 From which we deduce 



^E(BC) 



dt 



dt 



dt 



or 



and, therefore, 

 (2) 



If, then, we know the thermoelectrical power of different metals 

 in reference to a standard metal X, it will be easy to deduce from 

 this the thermoelectrical power of any two metals by the formula 



= </>(AX)-<HBX). 



Fig. 68. 



Let AX (Fig. 68) be the curve which represents the value of ^> 

 as a function of / for the two metals A and X, and BX the analogous 

 curve for the two metals B and X ; from equation (2) we shall have 



