EFFECT OF LIGHT ON ELECTEICAL CONDUCTIVITY OF SELENIUM. 369 



In the first column are given the times from the commence- 

 ment of exposure to the light, in the second column the 

 actual rise observed with red light at a distance of 100 

 centimetres, and in the third column these rises are 

 expressed as percentages of the total increase observed. 

 In the remaining colums the corresponding figures for the 

 other intensities are given. In the observations with the 

 green light, a galvanometer the sensitiveness of which 

 was twenty-one times as great as that of the one used with 

 the red light was used ; with this galvanometer satisfactory 

 readings could not be obtained in less than thirty seconds 

 after the commencement of the exposure. 



Table III. 



Time. 



100 Red. 



300 Red. 



600 Red. 



200 Green. 



5seconds 



2-82 = 54% 



0-58 = 



= 30% 



0-18 = 



= 17% 





10 „ 



3-58 69 



•87 



45 



•28 



26 





20 „ 



4-20 81 



118 



61 



•41 



38 





30 „ 



4'49 861 



1-36 



70 



•53 



49 



1-13 = 73% 



60 „ 



4-73 931 



1-65 



85 



•71 



66 



1-28 821 



1^- mins. 



•5-00 96J 



1-78 



92 



•81 



75 



1-34 86^- 



2 



5-12 981 



1-83 



94 



•89 



82i 



1-39 90 



3 „ 



5-18 100 



1-90 



98 



•97 



90 



1-44 93 



4 „ 





1-93 



99^ 



1-01 



931 



1-47 95 



o 





1-94 



100 



1-03 



95 



1-49 96 



7 „ 











1-08 



100 



1-52 98 



Total rise 



5-19 



1-94 



1-08 



1-55 



In figure 3 are plotted curves showing the relation 

 between the increase of conductivity and the time of 

 exposure to light, times, reckoned from the commencement 

 of the exposure, being set out as abscissae, and the corres- 

 ponding increases, expressed as fractions of the total 

 increase, as ordinates. A is the curve obtained with red 

 light at 100 cms., B, with red at 300 cms., C, with red at 

 600 cms., and D, with green at 200 cms. 



