﻿356 Mr. F. C. Toy on the Theory fo the 



have sensitivities between zero and I x (which is the number 

 operative when the intensity of the light is Ij) is given by 



Fig. 1. 



o i, 



the area OAB, i. e. 



i-» 



N,: 



J/ a)dI ' 



(1) 



where /(I) gives the values of the ordinates in terms of I ; or 

 if N is the average number of nuclei per grain and a the 

 number of grains in volume V, 



N, 



■-;J>.*. . . , 



(2) 



The total number of nuclei is given by 

 N=f/(I).c*I. 



Fig. 2. 



The curve showing the relation between N and I, shown in 

 fig. 2, is characterized by its unsymmetrical-shaped S form. 



