THERMOELECTRIC DIAGRAM. 



443 



seem to be iron and nickel, the curves for which have numerous 

 sinuosities. 



At the end of the volume is the diagram for the principal metals, 

 compared with lead as neutral metal. If the temperatures are 

 counted from the absolute zero, those curves give a very simple 

 representation of the quantities of heat disengaged in the circuit, 

 in various forms, during the passage of the current. 



Let us suppose that the curve A (Fig. 213) represents the thermo- 



T-P> 



electric power of a metal A. Equation 



H = T 



shows first that, at the temperature T, the difference of potential 

 of contact with the neutral metal is represented by the area of the 

 rectangle PQ. In like manner, the value of H, relative to the 

 temperature T 15 is represented by the rectangle P l Q l . Lastly, as 

 we have already seen (279), the electromotive force E, between the 

 temperatures Tj and T, is represented by the area of the curvilinear 

 trapezium MjP. The specific heat of electricity of the standard 

 metal being zero, we have (282) 



