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XIV. The Heat developed during the Absorption of Electrons 

 by Platinum. By 0. W. Richardson, M.A., D.Sc, 

 Professor of Physics, and H. L. Cooke, M.A., Assistant 

 Professor of Physics, Princeton University *. 



[Plate III.] 



§ 1. TN 1901 1 one of the writers showed that the pheno- 

 J_ mena attending the emission of negative electricity 

 by hot metals could be explained on the assumption that the 

 electrons which, on the electron theory of metallic conduction, 

 move freely inside the metal, attain sufficient kinetic energy 

 at high temperatures to enable them to overcome the forces 

 tending to keep them inside the metal, and so escape. From 

 the way in which the thermionic current varied with the 

 temperature it was shown that the difference, iv, in the value 

 of the potential energy when outside and when inside a metal 

 could be calculated. Somewhat later f it was shown that the 

 existence of this difference in the potential energy would 

 involve a loss of thermal energy by the substance when the 

 electrons were being given off, and it was pointed out that 

 this effect would increase very rapidly with the temperature ; 

 so that at sufficiently high temperatures the loss of energy 

 due to this cause would be greater than that arising from 

 thermal emission. An effect of this character has recently 

 been discovered by Wehnelt and Jentzsch §. 



Another consequence of the existence of this difference of 

 potential energy is that when electrons possessing negligible 

 kinetic energy pass into a metal an amount of heat should be 

 developed which is equal in magnitude to the difference in 

 potential energy for each electron multiplied by the number 

 of electrons entering the metal. The present experiments 

 show that this effect exists, and is of the expected order of 

 magnitude. 



On this view of thermionic emission, the loss of energy 

 when the electrons escape will consist of two parts : — ■ 

 (1), that due to the thermal kinetic energy of agitation of the 

 escaping electrons, and (2), that required to overcome the 

 work function, w.- Recent experiments show that the former 

 is equal to the kinetic energy of thermal agitation of a 

 molecule of gas at the temperature of the metal, and corre- 

 sponds, at any temperature which is available experimentally, 

 to the energy which would be acquired by falling through a 



* Communicated by the Authors. 

 t O. W. Richardson, Camb. Phil. Proc. vol. xi. p. 286. 

 X 0. W. Richardson, Phil. Trans. A. vol. cci. p. 497. 

 § Ann. der Pkysik [3] vol. xxviii. p. 537. 



