Memories of early day s in solid state physics a theory explaining the Hume-Rotheryt rules in metals and Herbert Skinner was engaged in his experimental work on the soft X-ray emission bands of light metals i think that when I went to bristol I must have been aware of Sommerfeld's explanation of the absence of a major contribution to the specific heat from the electrons, assuming that they obeyed Fermi-Dirac statistics, and the treatments by Bloch, Peierls and Wilson of electrons moving in a periodic field, the long mean free paths, the separation of the energy states into zones and the distinction be tween metals and non-metals. Looking back on it, I am surprised how easily everyone accepted this strange theory, in which all the electrons, in insulators as well as in metals, were treated as free, and insulators appeared as materials in which all the energy states in each zone were either occupied or empty, so that a current due to electrons moving in one direction was exactly balanced by movement in the opposite direction. The papers by Bloch and Peierls tell us something about that. Moreover, the approximation in which each electron moved in the average field of all the others was very easily accepted; I suppose Hartree's success with the self- consistent'fields for atoms had a lot to do with this. More detailed treatment of the effect of the very large interaction term e2/r1 had to wait till later The monumental and comprehensive report in the Handbuch der Physik by Sommerfeld Bethe appeared in 1933 and formed a basis on which other workers could build. This report, I believe, had an immense influence on solid state physics Apart from the effects of the interaction term e /r12 everything seemed to be there worked out in detail. Whether I had seen this report when Harry Jones showed me his work in 1933 I cannot remember, but i do remember the impact that Jones's work made on me, He supposed that all the electrons in an alloy could be treated as free, that the effect on their energies, particularly of those with states in k-space near the Fermi surface, could be calculated as in the theory of Bloch, and so be depressed when that surface approached the boundaries of the zone. An alloy would therefore take up a structure such that the boundary of a zone lay just outside the Fermi surface.(I do not believe we used the term 'Fermi surface at that time, only 'Fermi energy'. The idea of the Fermi surface was, however, well brought out in Bethe's article which contains very clear illustrations of their shape calculated for certain cases. )I think my enthusiastic acceptance of the theory was typical of my generation at that time; quantum mechanics was new, all physics and chemistry lay there to be explained and if by making approximations and neglecting even large terms(like e/ r12)one could account for something that had been observed, the thing to do was to go ahead and not to worry. I remember many discussions with Hume-Rothery himself, who shared my point of view Turning now to Skinner's work(some of it with O Bryan)on X-ray emission by the light metals lithium, sodium and magnesium, the observations showed band of the form illustrated in figure la. The theory of non-interacting electrons, as set out in Sommerfeld Bethe's article and neglecting correlation, predicted a form of the band, corresponding to the density of states, as illustrated in figure 1b-so t See note on Hume- Rothery at end of the article by H. Jones