concerning Voltas Contact Force. 



353 



their relative thermoelectric power at the junction, Pabt? may 

 be called P x ; and the area just spoken of is II 1 = PiT 1 . 



Fig. 1. 



Po=f'(ot)=o 



in 1856 that this H x is the 

 measures the reversible heat 

 unit quantity of electricity is 



Now Lord Kelvin showed 

 Peltier coefficient, i.e. that it 

 generated at the junction if a 

 transmitted across it. 



If we proceed to connect the two metals also at some other 

 point, at some other temperature T 2 , there will of course be an 

 appropriate value for P 2 and II 2 , but there is more than that : 

 every intermediate point of one metal will have a temperature 

 corresponding to that at some intermediate point of the other 

 metal, and accordingly there is a P and a II appropriate to 

 every intermediate temperature. 



There will also be now a closed circuit, and a current, 

 driven by a resultant electromotive force, which may be ex- 

 pressed instructively in the following different wavs, 



Eatj = 



<AB 



= cycle I Tdt= j ~P A b^ = | "iLHog T =/(/ 2 ) -/( 



*i) 



the function /being such that 



n AB =T/'(o=T 



At the junctions there is now 

 heat per second 



n 1 =T 1 /'(* 1 ) and n 2 =T 2 /'(t 



per unit current. 

 In the metals there 



7, Eab everywhere. 



i reversible generation of 



is likewise a reversible 



generation of 



heat 



©«=i <r a dt, <h) 6 =( Vftdf, 



