THERMO-ELECTRICITY 53 



New Metallurgy, that growth could have been 

 neither so rapid nor so sound had it not been for 

 the co-operation of another and entirely different 

 method of studying metals. This also had its 

 beginning in purely scientific research, dating back 

 to the earlier part of the nineteenth century, 

 when the "thermo-electric" properties of metals 

 were first studied by physicists. The fundamental 

 discovery in this case was a purely electrical one 

 it consists in the simple fact that where two 

 pieces of different metals touch one another, the 

 application of heat produces a small electric 

 current provided that the pieces of metal are 

 connected together so as to form a complete electric 

 circuit. Take the simplest case, of two pieces of 

 wire of different metals joined together at both 

 ends so as to form a closed loop. In such a loop 

 there are two " junctions" where the two metals 

 come into contact. If now one of these junctions 

 is kept cold while the other is heated, a small 

 electric current is caused to flow around the loop. 

 If the second junction were to be equally heated, 

 an equal but opposite electric flow would be pro- 

 duced and the two currents would neutralise one 

 another ; in this way the actual amount of current 

 which flows around such a circuit is in reality a 

 measure of the difference of temperature between 

 the two junctions. Attempts to obtain practical 

 applications of these facts were soon made ; in one 

 direction it was endeavoured to utilise the electric 



