132 



O. U. VONWILLER. 



was apparently greater when the current flowed in a 



negative direction, that is when it entered the silicon 



through the surface of greater area. The conductivity is 



much greater than that of selenium, so that it was possible 



to obtain accurate readings of the currents for very small 



differences of potential. On many occasions evidence of a 



minimum conductance for a small positive e.m.f. was 



obtained. 



Fig. 1. 



K 1H 



\_£ V 



V / ig jjU*< 



E lil 



tm 



Curve II, fig. 1, shows the relation between current and 

 e.m.f. in a case when a piece of silicon, roughly pyramidal 

 in form, was held between two brass plates, one at the 

 base and one at the apex ; the height of the pyramid was 

 2J centimetres. The change of direction of curvature does 

 not occur at the origin but some distance on the positive 



