CONDUCTION OF ELECTRICITY IN MOLYBDENITE. 231 



portional to the conductance. The curves show clearly the 

 marked difference in the effect of temperature changes in 

 the two cases. Here, as in a number of trials, the con- 

 ductance of BO has an approximately linear relation to 

 temperature during the greater part of the rise, but calcu- 

 lations of the temperature coefficient of the conductance 

 from such readings give widely different values in different 

 cases and even witii the same specimen in different trials. 

 The values indicated range from 0*003 to 0'009 per degree. 

 The only unvarying result is that the conductance increases 

 with rise of temperature and decreases with fall. 



In this work at high temperatures it was found that 

 small differences of temperature between the various con- 

 tacts with the molybdenite caused considerable trouble 

 owing to thernio- electromotive forces, until this source of 

 error was detected and removed or eliminated by actual 

 determination of the e.m.f., a simple matter with the aid 

 of the potentiometer. It was soon seen that comparatively 

 large e.m.fs. were obtained for small differences between 

 the temperatures of the junctions and an attempt was made 

 to measure this e.m.f. for known differences of temperature 

 of copper and molybdenite junctions. Four junctions of 

 copper and eureka wire were prepared by soldering together 

 the ends of wires of No. 40 gauge of the two materials, the 

 joint being made as small as possible, and the insulation 

 being removed over as small a length as would allow a 

 satisfactory join to be made. These junctions were clamped 

 against four points on a molybdenite strip, the junction 

 being pressed between a small piece of copper foil and the 

 molybdenite. A small brass terminal was clamped on to 

 one end of the molybdenite strip and this was heated by a 

 current passing through a coil of insulated wire wrapped 



