THERMIONIC ELECTRON EMISSION 475 



suming a Fermi-Dirac distribution in the metal at 3000° K. with 

 calculations based on a Maxwellian distribution. This comparison 

 also is shown in Fig. 24, curve 3. The circles were taken from a curve 

 by Bartlett and the line was calculated by equations (86), (87) and 

 (88). The two calculations agree, thus indicating that the assumption 

 of a Fermi distribution in the metal leads to the same result as the 

 assumption of a Maxwellian distribution. 



G. Miscellaneous Topics 

 In order not to lengthen unduly this review we have omitted a discus- 

 sion of a number of topics. Such topics have either been adequately 

 treated in the reviews and books referred to in the introduction or else 

 no significant advances have been made recently. Some of these 

 topics are: Secondary electron emission, high field emissions, thermi- 

 onics as related to photoelectricity and contact potential,* and cooling 

 and heating effects accompanying the emission or absorption of elec- 

 trons. In connection with the last topic we feel that a critical analysis 

 of how the quantities determined by experiment are related to the 

 work function and heat function should be made. Most of these 

 experiments were performed before the day of the Fermi-Dirac- 

 Sommerfeld contributions and should thus be reinterpreted. 



Acknowledgments 

 It gives me pleasure to acknowledge the help I have received in the 

 preparation of this article from my colleagues at the laboratories. 

 I acknowledge in particular the benefit of numerous discussions with 

 Dr. C. J. Davisson and Dr. W. H. Brattain and Mr. R. W. Sears. 

 Professor V. Rojansky, now at Union College, is responsible for some 

 of the more complicated equations used in the checkerboard theory. 

 Mr. R. W. Sears deserves a great deal of credit for his painstaking 

 efforts in preparing the figures and tables and in assembling some of 

 the data. 



References 



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2. S. Dushman, Rev. Mod. Phys., 2, 381 (1930). 



3. A. L. Reimann, Thermionic Emission, Aberdeen University Press, Aberdeen, 



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4. Muller-Pouillets, Lehrbuch der Physik, Vol. IV, F. Vieweg, Braunschweig, 1934. 



5. Wien Harms, Handhuch der Experimentalphysik, Vol. XIII, Part 2, Akademische 



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6. L. B. Linford, Rev. Mod. Phys., 5, 34 (1933). 



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* For a critical discussion of this relationship, see Becker and Brattain.^ 



