THE SCIENTIFIC WORK OF C. J. DAVISSON 797 



tinguished physicist, as one of the situations in which the concept of a 

 single sharp potential-drop becomes most palpably inadequate. Work of 

 this kind continued to be done, especially in Germany, until the later thir- 

 ties, and then regrettably flickered out. 



In 1937 the Nobel prize was conferred on Davisson, and he had the 

 opportunity of enjoying the ceremonies and festivities which are lavished 

 upon those who go to Stockholm and receive it. He shared the prize with 

 G. P. Thomson, who must not be entirely neglected even in an article 

 dedicated explicitly to Davisson. There was little in common between their 

 techniques, for Thomson consistently used much faster electrons which 

 transpierced very thin polycrystalline films of metal and produced glorious 

 diffraction-rings. He too founded a school of crystal analysts. 



Finally I mention three notes — two abstracts of papers given before the 

 American Physical Society in 1931 and 1934, and one Letter to the Editor 

 of Physical Review — bearing on what has been described to me, by an ex- 

 pert in the field, as the first publication of the principle of the ''electrostatic 

 lens" useful in electron-microscopy. These are joint papers of Davisson and 

 C. J. Calbick. They report, in very condensed form, the outcome of an 

 analysis which showed that a slit in a metal cylinder treats electrons as a 

 cylindrical lens treats light, and a circular hole in a metal plate treats elec- 

 trons as a spherical lens treats light : in both cases the field-strengths on the 

 two sides of the metal surface (cylinder or plate) must be different. Experi- 

 ments were performed to test the theory, and succeeded; and in the latest 

 of the notes we read that Calbick and Davisson used a two-lens system to 

 form a magnified image of a ribbon-filament upon a fluorescent screen. Cal- 

 bick recalls that the magnification was of the order of twentyfold. 



During the time of his researches on electron-waves, Davisson's office 

 was on the seventh floor of the West Street building, on the north side about 

 seventy-five paces back from the west facade: his laboratories were at times 

 beside it, at times across the corridor. This illustrates a disadvantage of our 

 modern architecture. If Davisson had done his work in a mediaeval cathe- 

 dral, we could mount a plaque upon a wall which had overlooked his appa- 

 ratus, and plaque and wall would stand for centuries. But the inner walls 

 of Davisson's rooms are all gone, and the outer wall consisted entirely of 

 windows; and nothing remains the same except the north light steaming 

 through the windows, which we may take as a symbol of the light which 

 Davisson cast upon the transactions between electrons and crystals. 



