CONDUCTION OE ELECTRICITY IN MOLYBDENITE. 233 



these trials was 80°. For temperatures between 16° O. 

 and 100° C. the e.m.f. for a difference of one degree between 

 two copper molybdenite junctions was found to be 560 micro- 

 volts. This is the mean value obtained from a number of 

 apparently satisfactory trials with several different speci- 

 mens; the extreme values found are about 10 per cent, 

 greater and less than this. No attempt was made to 

 determine the variation with temperature which was small 

 within this range. The direction of the thermo-electric 

 current is from copper to molybdenite at the hot junction. 

 The thermo-electric height of molybdenite is thus very 

 great, being comparable with those of silicon and selenium. 

 This result is of interest, because it is considered probable 

 that the variation of the contact resistances with size and 

 direction of current, which is the origin of the rectifying 

 property, is due to thermo-electric effects produced by the 

 passage of the current. 



The PJiysical Laboratory, 



The University of Sydney. 



