574 .Theory of Photoelectric Action. 



For small velocities o£ incident electrons, such as those 

 with which we are dealing, the proportion reflected increases 

 with increasing energy. It follows that out of a mixed 

 aggregate of incident electrons a greater proportion of the 

 slow ones will be absorbed th;m of the fast ones, and that 

 the proportion of incident electrons which is absorbed will 

 be greater than the proportion of their incident energy wnich 

 is absorbed. Thus s will be a positive quantity which is less 

 than unity. 



Equations (8) and (9) are independent of the particular 

 value of the index 2 of in equation (3). These equations 

 and the first part of (5 a), have been verified by experiments 

 made by Dr. K. T. Comoton and the writer *. A fuller 

 account of these experiments will shortly be published in this 

 journal f . 



Palmer Physical Laboratory, 

 Princeton, N.J. 



* Science, vol. xxxv. p. 783, May 17, 1912. 



f Note added during correction of proof . 



There do not at present appear to be any considerations which would 

 necessarily limit the applicability of the above methods, and the results 

 to which they lead, to the comparatively narrow field to which the term 

 photoelectric effect is usually restricted. For instance, there is no con- 

 clusive reason why they should not be applicable to the ionization pro- 

 duced by such radiations as the liontgen and y rays, if these differ from 

 light only in degree and not in kind. Moreover, the deduction makes no 

 essential use of the fact that the particles have been supposed to be 

 electrically charged ; so that somewhat similar laws may be expected to 

 characterize the reversible formation of gaseous chemical products under 

 the influence of aethereal radiations. 



Equations (1) to (9) have been derived without making use of the 

 hypothesis that free radiant energy exists in the form of " Licht-quanten," 

 unless this hypothesis implicitly underlies the assumptions : — (A) that 

 Planck's radiation formula is true ; (B) that, ceteris paribus, the number 

 of electrons emitted is proportional to the intensity of monochromatic 

 radiation. Planck (Ber. der Deutsch Physik. Ges. 1912) has recently 

 shown that the unitary view of the structure of light is not necessary 

 to account for (A) and it has not yet been shown to be necessary to 

 account for (B). It appears therefore that the confirmation of equations 

 (5 a), (8) and (9) by experiment would not necessarily involve the 

 acceptance of the unitary theory of light. 



The essence of the foregoing discussion has already been printed in 

 ' Science ' (vol. xxxvi. p. 57, 1912). 



In a recent paper Einstein {Ann. der Physik, vol. xxxvii. p. 832, 1912) 

 has come to- the conclusion that when a gas decomposes under the 

 influence of light of frequency v there is an absorption of energy hv for 

 each molecule or electron emitted. Einstein's argument appears also not 

 to be dependent on the unitary hypothesis, at any rate explicitly. 



