The Scientific Work of C. J. Davisson

HE very first piece of work which is published by a physicist who is destined to be great is not often outstanding; but sometimes it has curious affinities, accidental rather than causal, with aspects of the work t h a t was to come thereafter. In the first paper published by C. J. Davisson, we find him working with electrons, concentrating them into a beam by the agency of a magnetic field, directing them against a metal target, and looking to see whether rays proceed from the target. True, the electrons came from a radioactive substance, and therefore were much faster than those of his later experiments. True also, he did not actually focus the electron-beam. True also, the rays for which he was looking were X-rays, and in these he took no further interest. Yet in nearly all of his subsequent researches he was to use some of the principles of electron-focussing or electron-microscopy; in many, he was to look for things that were emitted by the target on which his electrons fell. This maiden papei was presented before the American Physical Society at its meeting in Washington in April 1909; the printed version may be found in the Physical Review, page 469 of volume 28 of the year 1909. It was signed from Princeton University, whither Davisson had gone as a graduate student. Another characteristic of Davisson's work in his later years was his frequent study and use of thermionics. Already in 1911 we find him working in this field--but it was thermionics with a difference. The word "thermionics" now signifies, nearly always, the emission of electrons from hot metals; but at first it included also the emission of positive ions from hot metals and hot salts.