276 THERMOELECTRIC CURRENTS. 



In this case equation (7) becomes 



and we deduce from it 



T 



We have further, for the neutral point, H n = 0, or 



which gives, finally, putting k' k = a and replacing the absolute 

 temperatures by ordinary temperatures, 



H = (K - )T(T n - T) = aT(t n - t), 



In this way we rediscover the empirical formulae of Sir W. 

 Thomson and of Gaugain. 



The thermoelectrical power of the two metals is then 



it will therefore be represented by a straight line as a function of the 

 temperature. 



Suppose we take the thermoelectrical powers in reference to the 

 same metal for which k is zero, which, according to Le Roux's 

 experiments, seems to be the case with lead, the equation reduces 

 to 





