372 



O. U. VONWILLER. 



of fall after different times of exposure in any instance 

 were very small however, so that the difference in the 

 behaviour of the cell with red and green light would be 

 practically the same for exposures of equal duration, pro- 

 vided that the maximum value had been obtained in each 

 case. 



In fig. 5 curves are drawn illustrating the results obtained 

 with cell 22, in a different manner. As abscissae are taken 

 the total increases in conductivity produced by exposure 

 to light of different intensities, expressed as percentages 

 of the conductivity in the dark, and as ordinates the frac- 

 tion of the total change produced in some given time. 

 Curves A and B give the fractions of the total rise produced 

 in 60 seconds and 30 seconds respectively, and curves C 

 and D give the recovery after the illumination has ceased 

 for the same times, red light being used in all cases. For 

 example, the point "a" shows that when the light was 

 such that it produced a chaDge in conductivity equal to 



