﻿270 Dr. L. Silberstein on a Quantum 



reality of these infringements which have been extensively 

 studied and condensed into empirical formulae by Abney, 

 SchwarzschiJd, Kron and others. But it has seemed inad- 

 visable to encumber the very beginnings of the proposed 

 theory by complicated details of such a kind*. 



The failure of the reciprocity law can more profitably be 

 taken up later on, after the fundamentals of the theory have 

 been somewhat solidified and extensively tested, and the 

 prospects of mastering the "failure" theoretically are by 

 no means averse, a very promising scheme seeming to lie 

 in the possibility (suggested by Joly and taken up by 

 H. S. Allen) of the liberated photo-electrons being regained 

 by some of the grains which were deprived of them by 

 previous impacts of light-quanta. In fine, the failure of the 

 reciprocity law as well as the facts known under the head of 

 " reversal " have at first to be neglected and considered 

 as future problems for the light- quantum theory united with 

 Joly's photo-electric theory, problems to which these com- 

 bined theories seem well equal. 



To pass to numerical facts, a short description will now be 

 given of the results of certain experiments undertaken in 

 this laboratory by A. P. H. Trivelli and Lester Righter f 

 which seem to corroborate the proposed theory most 

 emphatically. In order to have a much wider range of 

 sizes a than is usually afforded by the single grains, 

 Trivelli and Righter applied their counts and area measure- 

 ments to clumps of from one to as many as 33 grains, 

 basing themselves upon the well- supported assumption that 

 if one of the component grains be affected, the whole clump 

 is made developable. (This, at anj r rate, is the behaviour 



* R. E. Slade and G. I. Higson, " Photochemical Investigations of the 

 Photographic Plate," Proc. Roy. Soc. xcviii. pp. 154-170 (1920), on the 

 contrary, make the failure of the reciprocity law their point of departure. 

 They mention at the very beginning (p. 156) the possibility of a light- 

 quantum theory and write the Elder-type of formula in I, t, remarking 

 even that its coefficient would have a different value for each size of 

 grain, but being discouraged by or rather preoccupied with the failure 

 of the reciprocity law do not enter into the details of the probability 

 problem, which would have disclosed them the structure of that co- 

 efficient, and without much ado dismiss the quantum theory as 

 '* impossible." Independently of Slade and Higson the possibility of 

 a discrete theory (radiation in "filaments ") is mentioned by F. E. Ross, 

 Astrophys. Journ. vol. Hi. p. 95 (1920). Dr. Ross, without being 

 prejudiced against such a theory, notes even that it would lead ration- 

 ally to a mass-law, but does not enter into the details of the probability 

 problem and does not develop the theory. 



t For technical derails of these laborious experiments, see Trivelli and 

 Righter's own note in this issue of the Phil. Mag. p. 252. 



