654 



APPENDICES 



of electricity is produced in the -circuit. The 

 strength of the current is in proportion to the 

 difference of temperature of the junctions, and it 

 can be measured by means of a galvanometer. By 

 increasing the number of junctions the strength of 

 the current produced by changes of temperature 

 is proportionally increased. 



In tlie figure, if the junctions B B be warmer 

 than A A A, a current Hows in the direction in- 

 dicated and the needle is deflected, the degree of 

 deflection being in proportion to the strength of the 

 current. 



The thermopile thus converts a heat change 

 which is difficult to measure directly by a thermo- 

 meter, into an electrical change which can be 

 detected and measured with great accuracy by 

 means of a sensitive galvanometer. 



When the strength of the current is known, 

 the amount of heat can be calculated, since for 

 each thermopile there is a direct relationship 

 between the degree of difference of the tempera- 

 ture uf the junctions and strength of the resulting current. 



A A 



Fig. 246. 

 Diagram of Thermopile. 



i^ = Iron. 



I — I = German Silver. 



A, B = Junctions. 



G = Galvanometer. 



N = Needleof G. 



