Electrical Properties of Selenium. 253 



of Pt and Se between the finger and thumb. All the pieces 

 of Se with which they worked had had Pt wires fused into 

 their ends before being annealed. 



The following experiments point to a conclusion different 

 from that of Adams and Day. 



Exp. 28. — Experiments were made with three different 

 specimens of Se, all of which had been annealed for many 

 hours. None of these had electrodes fused into them. The 

 arrangements were varied in details, and the Pt-Se junctions 

 heated in different ways. In all cases the direction of the 

 thermo-electromotive force was from Pt to Se across the hot 

 junction. The direction of the current was not affected by 

 the addition of platinous selenide to the Se. 



Further experiments were made with the Se plate referred 

 to in the preceding section which had Pt wires fused into its 

 ends. 



Exp. 29. — The Pt wires being connected with the galvano- 

 meter, it was found that when one junction was touched with 

 the finger there was as usual a current from Pt to Se, but 

 that when the other was touched (that which had generated 

 the photo-electric currents in a former experiment) there 

 followed a current in the opposite direction — from Se to Pt. 



All the following observations were made with this anoma- 

 lous junction. 



Exp. 30. — The junction was heated by touching it first 

 with the pointed tip of a warmed glass rod and afterwards 

 with a hot copper wire. In both case& there resulted a cur- 

 rent in the normal direction — Pt to Se. 



Exp. 31. — A bent glass tube having a fine nozzle at one 

 end was heated over a Bunsen flame, and air was blown 

 through it from the mouth upon the junction. Result, an 

 abnormal current — Se to Pt. 



Exp. 32. — The last experiment was repeated, but the air 

 was driven through the tube by a foot-blower. Result, 

 normal — Pt to Se. 



Exp. 33. — The tube was allowed to cool, and when quite 

 cold air from the lungs was again blown through it. Result, 

 a current from Se to Pt stronger than that obtained with the 

 hot blast in Exp. 31. 



Exp. 34. — A small piece of sponge moistened with tepid 

 water was held upon the end of a wire near the junction but 

 not touching it. There immediately followed a small current 

 from Se to Pt. 



In short, the anomalous current from Se to Pt was in every 

 case clearly started, not by heat but by moisture. 



