RECTIFYING PROPERTY IN SILICON AND SELENIUM. 137 



The curves A + and B+ resemble the current voltage 

 curve obtained by Dr. W. H. Eccles (Phil. Mag., June 1910), 

 when a current passed through a film of iron oxide between 

 a point and plate. In this case the curve obtained was the 

 same for each direction of current, and the form of the 

 curve is shown by Dr. Eccles to be consistent with the view 

 that the passage of the current heats the film and decreases 

 its resistance, the resistance temperature coefficient of the 

 film being negative. 



If in the case of silicon the presence of a surface film of 

 some different material or structure is the cause of the 

 phenomena observed, its nature must depend upon the 

 direction of the current — possibly its formation may depend 

 upon the flow of the current — as the effects observed differ 

 to such a marked extent when the direction of the current 

 is reversed. With silicon the resistance of the main body 

 of the material was always very small in comparison with 

 the contact resistances, but with selenium cells of the 

 ordinary type the contact resistance is usually a relatively 

 small fraction of the total resistance. 



