RECTIFYING PROPERTY IN SILICON AND SELENIUM. 129 



some very positive evidence is available in the neighbour- 

 hood to substantiate the supposition. 



In the neighbourhood of Botany Bay there has been no 

 very definite evidence of elevation in Pleistocene times yet 

 discovered, nor does there appear to the author to be any 

 reason for assuming it, unless the actions we see going on 

 around us every day should be insufficient to account for 

 the phenomena of the past. 



NOTES on the RECTIFYING PROPERTY in SILICON 

 and SELENIUM. 



By O. U. VONWILLER, B.Sc, 

 Assistant-Professor of Physics in the University of Sydney. 



[Read before the Royal Society of N. S. Wales, September 3, 1913.] 



Some time ago when working with a selenium cell consist- 

 ing of a thin sheet of conducting selenium extending 

 between two parallel platinum wires, two millimetres 

 apart, the writer observed that the conductance apparently 

 varied with the direction in which the current passed. As 

 is usually the case with selenium cells, Ohm's law did not 

 hold, but instead of the conductance rising, it was found 

 that for one direction of the current the conductance 

 decreased at first as the e.m.f. was increased, rising for 

 higher values. When the current passed in the opposite 

 direction the conductance rose as the e.m.f. increased from 

 the lowest values. The minimum value of the conductance 

 was obtained for an e.m.f. of about one volt and was 0*97 

 of the value for zero voltage. For an e.m.f. of two volts 

 the current in one direction was ten per cent, greater than 



I— September 3, 1913. 



