EFFECT OF LIGHT ON ELECTRICAL CONDUCTIVITY OF SELENIUM. 373 



222°'° of the initial value, '855 of that change occurred in 

 60 seconds, "b" shows that *695of the change occurred in 

 30 seconds and so on. When green light was used the 

 corresponding curves are given by A' B' C and D' respec- 

 tively. For the curves A,B, A' and B\ the figures obtained 

 w r hen one side ODly (D L ) is exposed to the light are taken 

 and for the curves C, D, C and D' the results obtained after 

 both sides have been exposed are used. 



These curves show in a marked manner the difference in 

 the initial rates of rise and fall when using light of different 

 colours and the point already noted, the relatively slower 

 rise towards the end with green is also illustrated; for 

 example with a certain red light we see that 69j°/° of the 

 rise occurred in 30 seconds, and with a certain green light 

 68i 5 / j occured in the same time, but in 60 seconds 85J°/° of 

 the total change had been produced with the red and only 

 79°/° with the green ; similar results are noticed in the curves 

 for the falls of conductivity. 



This relatively slower rise towards the end is shown in 

 Table IV in which the rises observed after different dura- 

 tions of exposure are given for different intensities of 



illumination. 



Table IV. 



Colour. 





Distance of Light. 



100 cms. 



200 cms. 



300 cms. 



600 cms. 



Red 



Green 



Ptise in 3 mins 



n ® ii 



Difference ... 

 Total rise 



Bise in 3 mins. 



.„ io „ 



Difference ... 

 Total rise 



5-18 



5-19 



•01 



519 



3-47 



3 82 



•35 



3 83 



1-72 

 1 94 



•22 

 1-94 



1-90 



1-94 



•04 



1-94 



M0 



1-24 



•14 



1 24 



0-97 

 103 



•06 

 1-08 



The readings with green light are to be divided by 21 in 

 order to be on the same scale as those with red. 



