﻿266 Dr. L. Silberstein on a Quantum 



be seen presently that such an assumption is too narrow and 

 unnecessarily so. 



In fact, substituting the number n of light-quanta from 



equation (1), the exponent s* will become s = y-i?X, or, if 

 we put for brevity 



f3 = ot/hc, . (9) 



which may be considered as a constant, 



s=/3E.a\ (10) 



Here E is the incident light energy (exposure) and X the 

 wave-length of the light assumed to be monochromatic. 

 Thus the sensitivity exponent would be directly proportional 

 to the wave-length, and the number k would, for constant 

 E and a, increase steadily with the wave-length of the 

 incident light up to the photoelectric critical value X c and 

 then drop suddenly to zero, 



k 



j r = l-e- const -\\<\ n 



k =0, X > X c . 



Now, such a sensitivity curve does not seem to resemble the 

 familiar experimental sensitivity curves which show a more 

 or less gentle maximum followed by a gradual decrease 

 down to zero. It is true that such experimental curves | 

 represent the resultant effect due to grains of a whole range 

 of sizes, so that the k — X curve belonging to a single class 

 of (equal) grains may well be of the said abrupt type, — a 

 question to be decided only by micro-spectrographic experi- 

 ments and counts now in progress. Yet it seems advisable 

 even at this stage to provide for the possibility of smooth 

 maxima preceding the critical wave-length X c . 



This might be obtained by attributing to grains of different 

 sizes different values of X c . For then, although the curve 

 of each grain class would end abruptly , the superposition of 

 such curves ending over a range of different abscissae, might 

 properly displace and smooth out the resultant maximum. 

 The correctness of such an assumption (X c a function of a) 

 can at any rate be tested by direct experiments %. 



* s/JE can be referred to as the u sensitivity exponent." 

 t Apart from the fact that they are not taken for E= const. 

 \ Preparations for such experiments are now being made in this 

 laboratory. 



