342 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



molybdenite, or it may be due to structural differences from point to 

 point of the crystal. I have not yet investigated the question of the 

 cause of the variability of the phenomenon. The differences in the 

 specimens could not have arisen from the copper-plating or from 

 the heat employed in soldering the junctions, because the specimens 

 A, B, C, and D were tested before the copper-plating and soldering 

 was done, and by means of the preliminary test were classified as 

 positive, negative, positive and negative respectively, which agrees 

 with the determination after soldering. 



TABLE IX. 



Molybdenite-Copper Junctions A, B, C, D. The Cold Junction was at 

 20° C. The Hot Junction was at Temperature T° C. The Thermo- 



ELECTROMOTIVE FORCE V IS IN MILLIVOLTS. 



The preliminary test was made by touching the specimens with two 

 copper wires attached respectively to the two terminals of a galvanom- 

 eter, one of the wires being slightly warmer than the other. This pre- 

 liminary test proved very interesting in that it shows that one may find 

 all over many of the pieces cut from a crystal of molybdenite points 

 where the substance is thermoelectrically positive and other points 

 where it is thermoelectrically negative. These positive and negative 

 points sometimes lie so near together that with a fine-pointed exploring 

 electrode attached to a galvanometer and warmed by heat conducted 

 from the hand, one may find the deflections of the ' galvanometer re- 

 versed from large positive values to large negative values on making 

 the slightest possible motion of the pointer over the crystal. 



Explorations of this kind failed to show any definite orientation of 

 the thermoelectric quality with respect to the crystallographic axes. 



The existence of small thermoelectrically positive and negative 



