﻿Characteristic Curve of a Photographic Emulsion. 361 



the silver bromide. In fig. G are given some examples of 

 grains in which these nuclei appear ; they are formed more 

 on the edges of the grains than anywhere else, though quite 

 a number appear either inside or on the flat surfaces. 



Fig-. 6. 



Positions of nuclei numbered. 



The next experiment was to show if equation (6) holds 

 good. A plate was exposed to a uniform intensity, partially 

 developed, and the number of nuclei occuring on each of 

 150 grains was counted. Hence the average number per 

 grain was known and also the number of grains having 0, 1, 

 2, 3, etc. nuclei each. 



In Table II. are given the theoretical and observed values 

 of P,. for two equal-sized sets of grains, in one and the same 

 emulsion, having widely different values of N . 



Table II. 



N = 0-180. 



N = 1-193. 



Value 

 of r. 



No. grains 

 having r 

 nuclei. 



Probs 



Obs. 



ability 

 Pr. 

 Calc. 



Value 



i of r. 



No. grains 

 having r 

 nuclei. 



Probability 

 Obs. Calc. 







91 



O607 



0619 



i 



43 



0-287 0303 



I 



47 



0313 



0297 



1 



55 



0-367 0362 



2 



11 



0073 



0071 



2 



36 



0240 0-216 



3 



1 



0007 



0001 



3 



12 



0-080 0-086 



4 







0000 



0001 



4 



4 



0-027 0-026 



The observed values of P r were determined by the fact that 

 the probability of a grain having r nuclei is equal to the 

 fraction obtained by dividing the number of grains which 

 have r nuclei by the total number, i.e. 150. In fig. 7 the 

 theoretical values are represented by the smooth curves, and 



