Proc R. Soc. Lond. A 371, 56-66(1980) Printed in great Britain Memories of early days in solid state physics BY N.F. MoTT, F R S Cavendish Laboratory, cambridge Mott, Sir Nevill. Born Leeds 1905. Studied theoretical physics under R. H. Fowler in Cambridge, in Copenhagen under Niels Bohr and in Gottingen. Professor of Theoretical Physics in Bristol 1933-54, and Cavendish Professor of Physics, Cambridge 1954-71. Nobel Prize for Physics 1977. Author of several books and research papers on application of quantum mechanics to atomic collisions an since 1933 on problems of solid state science My interest in the subject began in 1933 when I left Cambridge to take up the chai of theoretical physics in Bristol In Cambridge I remember that A H. Wilson wrote an Adams prize essay on metals which led to his book, The theory of metals, and I have a curiously vivid recollection of R. H. Fowler explaining to C. D. Ellis that most semiconductors were what we would now call extrinsic, the electrons coming from impurities, and Ellis replying " very interesting in a tone of voice that implied that he was not very interested. Although a lecturer in the Faculty of Mathematics as were at that time all theorists in Cambridge, I spent much of my time in the Cavendish, and in Fowler's massive book on Statistical Mechanics Rutherfords Cavendish was not the place where a young man would naturall turn to the theory of electrons in solids. I do not remember being very interested myself, but I do remember going to a course of lectures by the late Ebenezer Cunningham of St John's College on electrons in metals when I was an under graduate; t our textbook was Richardsons Electron theory of metals. I re member being struck by the point in the book and in the lectures that the Hall effect gave an indication of the number of free electrons in a metal, often near one er atom, and that at least one quantity, the ratio of thermal to electrical conduc tivity, could be calculated; but there were many unexplained observations, parti- cularly the long mean free paths and the absence of any large contribution to the specific heat from the electrons. But most of all I wondered how it could be that the atoms of a metal gave up their electrons, so that they became free, while in an insulator they remained fixed in position and unable to move. t This was of course cleared up by wilson's work. When I went to Bristol in 1933 as Professor of Theoretical Physics, two influences turne he towards electrons in solids: Harry Jones(see the previous paper) had t Probably in 1925; J. C. Slater in his Scientific biography records that Dirac attended the same courge in 1923 t My recollection contrasts with Wilson' s in this volume of discussions at L feeling that an insulator is a'poor'metal. As far as I can remember, w period that in'insulators', temperature would be capable of allowing electrons to move [56]