C. Herring ith interest, as I began to think about possible band structures for the semi conductors silicon and germanium which were being intensively investigated t Bell Laboratories, where I now was. After finishing this diamond work and moving to R.C.A., Herman collaborated with a graduate student at Princeton,J Callaway, in applying similar methods. to the band structure of germanium As just noted, there was, in the late 1940s and early 1950s, a great deal of interest in energy bands, especially in valence and conduction band edges, in germanium and silicon. In the early part of this period, many theoretical discussions simply assumed'for simplicity'that the band edges would be at the centre of the Brillouin zone, and would be non-degenerate, with isotropic effective masses. My experience with calculations for beryllium, and in due course my awareness of the results Herman was getting for diamond, convinced me that such a picture for the electron and hole states in silicon and germanium was extremely unlikely.However,there remained many possibilities, and it took some years to sort them out. Transpo properties, particularly the anisotropy of magnetoresistance in single crystals seemed to provide some of the most promising handles. Early successful uses of this approach were my collaboration with G. L. Pearson to infer from his exper ments that the conduction band edge in silicon was on the A lines with a mass anisotropy of five to one, and the inference by Meiboom Abeles that the condt tion band edge in germanium was at the L points, with a much larger mass anisotropy. Both these conclusions were soon confirmed by cyclotron resonance experiments. The magnetoresistance approach was less successful for the valence bands. I became convinced that the valence band edges in germanium must be along the A lines, because of the vanishing magnetoresistance for magnetic fields in the [100] directions. Such vanishing would have to occur from symmetry for [100] valleys, but could occur only by accident for many other band structures, including the a priori plausible one of a degenerate band edge at k=0. It turned out that just thisaccident' does in fact occur. By the middle 1950s, elucidation of the band structures of semiconductors was proceeding fairly rapidly, thanks primarily to cyclotron resonance, but also to such things as piezoresistance, optical properties etc. these provided a wealth of opportunities for comparing theory and experiment By contrast, there had not occurred any great expansion in opportunities for comparing theoretical band structures with experimental data for the case of metals There were still the old standbys: electronic specific heat, paramagnetic suscepti bility, some features of optical absorption, etc, but the great modern science of Fermiology had not yet been born. One new thing, however, did along about this time: the Knight shift. C. H. Townes, who had been a colleague of mine at Bell Laboratories in the late 1940s, had moved to Columbia University, and got involved in the newly blossoming field of nuclear magnetic resonance. Working at Brookhaven, a student of his, W.D. Knight, discovered that the n. m r. frequencies of nuclei in metals are usually appreciably greater than the frequencies of the corresponding nuclei in non-metallic compounds. Townes proposed the interpre tation that the field on the nucleus was enhanced by the contact hyperfine term