On the Reflection of Electrons by Metallic Crystals

trons impinging on the surface of a metallic crystal. The results for a simple special case of the general problem were published in 1939 . Thereafter the work on the general problem continued intermittently, and it was almost completed by the early part of 1942, when it was brought to a halt by the onset of wartime activities. Since then nothing has been done on the problem, and the results already obtained have never been published in extenso. However, C. Herring and M. H. Nichols have included an illuminating discussion of some of the more significant of the results in their recent monograph on thermionic emission . Although the intervening years, by bringing new problems in physics to the fore, have caused this work to lose some of the interest which it possessed at the time it was being done, it still seems to be worth while to put the full results upon record. The present occasion, when his friends and former colleagues are celebrating Dr. Davisson's seventieth birthday, is an especially appropriate one for this purpose. 2