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XII. r llie Influence of Temperature upon Photo-electric Effects 

 in a Very High Vacuum, and the Order of Photo-electric 

 Sensitiveness of the Metals. PyTi. A. Millikan, Associate 

 Professor of Physics in the University of Chicago, and 

 Geoege Winchester, Assistant in Physics at the University 

 of Chicago *. 



1. JNTRODUCTION.— -Two views have been advanced 

 regarding the mechanism of the discharge of cor- 

 puscles for metals under the influence of ultra-violet light. 

 According to the first view, the discharged particles are the 

 free or " metallic " corpuscles of the body which, by absorb- 

 ing the ultra-violet light, acquire sufficient kinetic energy to 

 enable them to escape from the attraction of the metal t- 



According to the second view, the escaping electrons are 

 not free from the atoms before their escape from the metal, 

 but are rather constituents of complex atomic systems which 

 become unstable under the influence of the ultra-violet light 

 and project electrons from themselves with velocities not 

 greatly different from those which these electrons possessed 

 w r ithin the atom {. 



If the first view is correct, then it is to be expected that 

 the ease with which the corpuscles escape from a given 

 metal, and therefore the number which escape per second 

 under the influence of a given source, will be an increasing 

 function of the temperature ; for " the higher the tempera- 

 ture the greater would be the initial kinetic energy possessed 

 by the corpuscles, and the smaller the increment required to 

 enable them to escape from the metal/'' 



On the other hand, if the second view is correct, it is not 

 to be expected that the rate of discharge will be affected at 

 all by temperature changes, since both the independence of 

 radio-activity upon temperature, and the fact that the ratio 

 of the specific heats of mon-atomic gases by constant pressure 

 and by constant volume reaches the theoretical limit, namely 

 1*67, constitute strong evidence that the internal energy of 

 the atom is not affected in any way by temperature changes. 



It is very important, therefore, from the standpoint of the 

 theory of photo-electric phenomena to determine definitely 

 whether photo-electric effects are or are not dependent upon 



* Communicated "by the Authors. This paper was read before the 

 meeting of the American Physical Society held in Chicago on Nov. 30, 

 1906. 



+ ' Conduction of Electricity through ^Gases/ J. J. Thomson, Chap. x. 

 'Die Elektrizitat in Gasen,' Johannes Stark, p. 112. Ramsay & Spencer, 

 Phil. Mag. xii. p. 417 (1906). 



X Lenard, Ann. d. Phys. ii. p. 355 (1900); yiii. p. 149 (1902); xii. 

 p. 449 (1903). 



