produced by changes of' Temperature. 



311 



upon either of them, a tiling which at present is impossible ; 

 but by the aid of what precedes, by taking for the point of 

 departure the electric state of the two metals, both at the zero 

 of temperature, we may discover what modifications that state 

 experiences, either by increasing or diminishing it at the same 

 time in both metals. This is the only means of arriving at a 

 knowledge of what takes place in the electric effects of con- 

 tact, until the combination of the metals begins to operate. 



Circuits are formed with wires of different metals, by mak- 

 ing the wire of the apparatus enter into it ; and the whole is 

 so disposed, that its two extremities may communicate with 

 the same metal, the only means of annulling its action on bo- 

 dies submitted to experiment. These wires have the same dia- 

 meter, about the third of a millimetre. The temperature is 

 then raised, and we operate as above described. The results 

 are given in the following table : — 



