Prof. W. G. Adams on the Action of Light on Selenium, 1M 



With stronger currents this ratio was found to diminish* 



On magnetizing the wires transversely by sending a current in 

 the direction of their length, a diminution of resistance was also ob- 

 served, which diminution also increased when the strength of the 

 current was increased. 



When a current was sent along the wire itself, on increasing 

 the current there was found to be also a diminution of resistance 

 in the case of hard steel, and an increase of resistance in the case 

 of soft iron and soft steel. 



Thus the effects produced are the same as those due to trans- 

 verse magnetization by a neighbouring current. 



Conclusions to be drawn from the experiments : — 



(1) The effect of passing any current through a bar of hard steel 

 is to diminish its resistance, and through a bar of soft iron or soft 

 steel is to increase its resistance. 



(2) When a bar of hard steel is magnetized by sending a current 

 through a coil which encloses it, there is a diminution of re- 

 sistance which is directly proportional to the square of the mag- 

 netizing current up to a certain limit. 



(3) When soft steel or soft iron is magnetized longitudinally or 

 transversely, there is an increase of resistance which is nearly pro- 

 portional to the square of the magnetizing current. 



" The Action of Light on Selenium." By Prof. W. G. Adams, 

 M.A., P.E.S. 



The paper contains an account of several series of experiments 

 made in December and January last on this subject with the 

 idew :— 



(1) To determine whether the change in the electrical resistance 

 f the selenium is due to radiant heat, light, or chemical action. 



(2) To measure the amount of the change of resistance due to 

 exposure to light from different sources and through various ab- 

 sorbing media. 



(3) To determine whether the action is instantaneous or gra- 

 dual, and, if possible, to measure the rate at which the action takes 

 Dlace. 



The selenium formed one of the four resistances in a Wheat- 

 stone's bridge ; and its average resistance was about 2| megohms. 



The two resistances in the bridge, which were kept constant, 

 ;vere 4 and 2000 ; so that the resistance of the selenium was 500 

 :imes the variable resistance required to balance it. 



E is taken to represent this resistance required to balance the 

 selenium. The box containing the selenium was laid on its side 

 md had a draw-lid, which was kept closed except when exposure 

 vas made. In front of the draw-lid was a black screen with an 

 )pening opposite to the selenium 6 centims. by 3 j centims., in which, 

 )r in front of which, various absorbing media could be placed. 



The absorbing media employed were bichromate of potash, sul- 

 phate of copper, ruby, orange, green, and blue glasses. Plates of 

 ock-salt, alum, mica, and quartz were also employed. 



M2 



