404 Piofs. Richardson and Cooke on the Heat liberated 



It was unnecessary to cany out the experiment for smaller 

 velocities as the effect", if it existed, would scarcely show 

 itself in this region. A few experiments were also tried 

 when the total leak due to the arc was twice as great as that 

 due to the H 2 discharge, but they still led to the same 

 result. 



This result points to the conclusion that each electron 

 emitted from a surface illuminated by ultra-violet light is 

 associated with only one frequency in the beam of light, and 

 its velocity is quite independent of the presence or absence 

 of waves of different frequency in the beam. 



Summary, 



1. The ultra-violet spectrum of mercury, investigated 

 electrically, extends to about X 1230. 



2. There is no appreciable radiation from the mercury arc 

 between A, 1450 and X 1780, 



3. The hydrogen discharge has relatively more energy in 

 the short wave-lengths than the mercury arc. 



4. The velocity of the electrons due to one wave-length 

 is independent of the presence of other wave-lengths in the 

 beam of light. 



I have much pleasure in thanking Professor Sir J. J. 

 Thomson for his suggestions and interest during the course 

 of the work. 



Cavendish Laboratory, Cambridge. 

 Jan. 9th, 1911. 



XL VIII. The Heat liberated during the Absorption of Elec- 

 trons by Different Metals. By 0. W. Richardson, Professor 

 of Physics, andH. L. Cooke, Assistant Professor of Physics, 

 Princeton University* . 



IN a recent paper t under a similar title the authors showed 

 that when slow moving electrons were received by a 

 platinum strip, part of the heat developed was independent 

 of the kinetic energy of the electrons. This production of 

 heat was explained as the thermal equivalent of the difference 

 in the potential energy of the electrons inside and outside 

 the metal. The present paper describes the results of similar 



* Communicated bv the Authors* 

 t Phil. Mug-. July 1910. 



