410 Heat liberated daring Absorption of Electrons by Metals. 



For the reasons which have been stated we have found it 

 impossible to test this question directly, up to the present. 

 The present theory o£ these phenomena requires that the 

 heating effect should be practically independent of the metal 

 receiving the electrons, as one of the authors has already 

 pointed out*. It is satisfactory to know that our experi- 

 mental results, so far as they go, do not conflict with the 

 theory. 



In our previous paper we omitted to take into account the 

 possibility of the existence of an electric field between the 

 osmium and the platinum arising from an intrinsic electro- 

 motive force ; and this omission led us to identify the heating 

 effect with the work done when the electrons escape from hot 

 platinum. The identification should be with the work done 

 when the electrons escape from hot osmium. This quantity 

 has not been measured yet, but we propose to measure it in 

 the course of our investigation of the thermionic properties 

 of osmium already referred to. 



The most important facts which we have so far established 

 are : — 



(1) The heating effect due to the difference of the potential 

 energy of an electron inside and outside of a conductor, which 

 we previously established for platinum, occurs in the other 

 metals. 



(2) The effect is of the same order of magnitude in all 

 cases, the measured values ranging from about 4'5 to 

 7-5 volts. 



(3) The values are influenced very considerably by the 

 nature and state of the thermionic emitter. (The experiments 

 do not preclude the possibility that the true effect is almost 

 independent of the metal receiving the electrons.) 



(4) The measured effect is not influenced by changes in the 

 pressure of the residual gas in the apparatus, provided this be 

 reasonably low. 



(5) Under certain conditions, not yet completely deter- 

 mined, the thermionic emission from osmium becomes un- 

 stable ; and there are two ranges of stability, one at low and 

 the other at high temperatures. 



We are glad to take this opportunity of thanking Messrs. 

 Baldwin, Carter, Critchlow, Ferger, Frederick, and Gibbs 

 for again assisting in taking the very numerous observations. 



Palmer Physical Laboratory, 

 Princeton, N.J. 



* 0. W. Richards jn, Rapports du Congres Int. de Radioloqie, Bruxelles, 

 1910. 



