﻿. On the Stark Effect for Strong Electric Fields. 371 



Summary. 



A theory is advanced which explains the relation found 

 experimentally between the number of geometrically identical 

 silver halide grains made developable and the light in- 

 tensity. It is assumed that there exist in the grains particles 

 which are not silver halide, and which are formed during 

 precipitation and subsequent ripening. With any normal 

 exposure (i. e. one which gives a value between and 100 

 for the percentage of developable grains), it is these particles 

 which form the reduction nuclei, the only action of the light 

 being to change their condition in such a way that they 

 become susceptible to the action of the developer. Each 

 nucleus does not necessarily require the same intensity to 

 change it. The nuclei are scattered haphazard amongst the 

 grains according to the laws of chance, and only grains 

 which have at least one will be developable. The sensitivity 

 of a grain is the sensitivity of its most sensitive nucleus. 



The effect of a variation of grain size is explained, and it 

 is shown that Svedberg's assumption regardiDg the similaritv 

 of the light-sensitive material in large and small grains is 

 not in agreement with the experimental facts in the case of a 

 fast emulsion. 



M 



XXXII. On the Stark Ejfeet for Strong Electric Fields. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, — 



Y attention has been drawn to the results of experi- 



ments by Takamine and Kokubu * in which an effect 

 of the nature indicated in a recently published paper t of 

 mine was detected, namely, a shift of the central line in the 

 perpendicular component of Hy in a strong electric field. 

 Before comparing the experimental amount of this shift 

 with the theoretical value it would have on the Quantum 

 theory of spectral lines,, it is necessary, however, to point 

 out a slip in my paper referred to above : thus on p. 945 

 a term is missing from the value of: the contour integral (4), 

 instead of (6) the full value should be 



f = B D /3B* \ 5BD*/ 7B»\^ 



* "The Effect of an Electric Field on the Spectrum Lines of 

 Hydrogen," I'art III. Memoirs of the College of Science, Kyoto 

 Imperial University, vol. iii. p. 271 (1919). 



t Phil. Mag. xliii. May 1922, p. 943 ; this will be referred to freely. 



2 B 2 



