BISHOP. — THERMAL CONDUCTIVITY OP LEAD. 



681 



nals of a standard ohm, consequently the resistance in this case in series 

 with the galvanometer was zero. It therefore became necessary to 

 introduce into the galvanometer circuit when calibrating it a resistance 

 equal to the nickel leads. This was done by means of two mercury 

 cups which were connected by a coil of copper wire, thus eliminating the 

 possibility of any additional thermo-electromotive force. The resistance 



20 



30 



40 



80 



50 60 70 



Temperatures Centigrade. 



Figure 5. 

 Diagram of Thermo-Electric Force. 



90 



100 



of the nickel leads was determined to a hundredth of an ohm, it being 

 shown that a change of this amount in the galvanometer circuit produced 

 a negligible change in the deflection. 



4. Thomson effect. — The resultant thermo-electromotive force per 

 degree is the sum of the Seebeck and Thomson effects. It is to be noted 

 that the conditions in determining the electromotive force are almost 



