218 PROCEEDINGS OP THE AMERICAN ACADEMY 



special cases considered, it seems probable that it exists for all cases 

 where there is a sensible variation of temperature between points 

 whose distance is witliin the limits of molecular action. It obviously 

 differs from both the Thomson and Peltier effects. 



Several properties of this effect can easily be deduced. In the first 

 place, since in general the current is caused entirely by it, — the 

 Thomson effect producing equal and opposite electromotive forces, — 

 if the effect obeys the ordinary thermodynamic laws, it must exist 

 so as to cause an absorption and an evolution of heat at the plane of 

 abrupt variation. Tiiis is not the only case of a thermodynamic 

 arrangement where the evolution and absorption take place at one 

 plane. In a thermo-electric circuit which has two neutral points, and 

 in one metal of which the Thomson effect is null, if the two junctions 

 are maintained respectively at the temperatures of the neutral points, 

 all the heat effects take place in one metal, and if the circuit is so 

 arranged that the change of temperature takes place across a plane, 

 then all the effects occur at this plane. 



If we call the new effect ^{T), the general equations for a circuit 

 where there exists one abrupt variation of temperature become : — 



-[/{W-r.(^,-7;)] +f^dT+ ar,(T, - T,) + ^ {T,) 



T^) 



To Ti 



The first parts of these equations are identically zero : — 



-•i -'o 



The latter equation shows that <J> ( 7^) is proportional to T. The 

 electromotive force is then proportional to the difference of tempera- 

 ture between the two surfaces of the plane. 



The chief practical uses of thermo-electricity are in the measure- 

 ment of high and low temperatures, and in the conversion of the 

 energy of heat into that of an electric current. The measurement of 



