The Conception and Demonstration of Electron Waves * 



By C. J. DAVISSON 



An attempt Is made in this article to trace the growth of our ideas 

 regarding the electron from their inception less than a hundred years ago 

 to the present day. The discussion begins with a consideration of the 

 vague and tentative deductions concerning an ultimate electrical charge 

 which became possible when Faraday revealed the laws of electrolytic 

 conduction; it touches upon the clarification of the conception of the electron 

 as a charged particle capable of independent existence and subject to the 

 laws of classical electrodynamics which was effected at the close of the 

 last century and the beginning of the present one by the researches of J. J. 

 Thomson and others; it indicates the difficulties in which this conception 

 became involved, and the attempts made by Planck, Bohr and others to 

 extricate it from them. The latter part of the paper is devoted to the 

 amplified conception of the electron which has been developed during the 

 last decade — a conception in which electrons are recognized as having, in 

 different circumstances, the properties of both waves and particles. 



Introduction 



IT is my purpose in this report to describe a few experiments, typical 

 of several hundred now recorded, in which streams of electrons ex- 

 hibit the properties of beams of waves. It seems desirable, however, 

 to begin by briefly reviewing various steps in the development of our 

 conception of the electron before about the year 1925. It is against 

 this background only that the phenomena revealed by the experiments 

 to be described appear in true relief. 



The idea that electric charge is granular was not new at the time of 

 the first International Electrical Congress in 1881. Faraday had 

 determined and announced the laws of electrolytic conduction fifty 

 years earlier, and it was recognized, by some at least, that these laws 

 suggested the existence of an elementary charge or atom of electricity. 

 An estimate of the magnitude of this natural and presumably ultimate 

 unit of charge had indeed been made a few years prior to the Congress 

 by the Irish physicist Stoney from such data as were then available. 

 The word "electron " to designate the hypothetical atom of electricity 

 was not, however, introduced until the year 1891. The concept of the 

 electron gained rapidly in sharpness in the decade next following — the 

 last of the century — not so much indeed from the introduction of new 

 ideas concerning it as from experimental evidence in support of ideas 

 already held. 



It was no new idea, for example, that neutral atoms contain positive 

 and negative charge in equal amounts, and that the ions of an electro- 

 lyte are merely atoms or groups of atoms in which these charges are 



* Presented by title at The International Electrical Congress, Paris, France, July 

 5-12, 1932. 



546 



