LAWS, BISHOP, AND MCJUNKIN. THERMAL CONDUCTIVITY. 461 



stancy of 0.0 1°C. The temperature is observed by a thermometer read 

 with a telescope. 



Calibration Apparatus. 



In order to determine the relation existing between the difference of 

 temperature of the inside and outside junctions, and the corresponding 

 E. M. F., the two hemispheres are removed from the apparatus and 

 maintained at different known temperatures, while metallic contact is 

 obtained between them by a piece of the same iron as the sphere. 





The calibration tank (Figure 2) is a box 12" X 24" X 10" deep lined 

 with tin and separated into two compartments by a double tin partition, 

 the space being filled with asbestos to prevent conduction of heat from 

 one to the other. 



Each compartment is provided with two fans to agitate the liquid, an 

 electric heating coil, and a coil of lead pipe through which steam or cold 

 water can be forced. Thus each compartment can be maintained at any 

 desired temperature. 



One hemisphere is placed on an insulating stand in each part of the 

 calibration tank. These are connected by a small piece of iron from the 

 original casting in the form of a U ^" in cross-section, each leg 1" long 



