The book I read during that year in London was Heitler, Quantum Theory of Radiation, that was the main thing. That was an excellent book. It described quantum electrodynamics as it existed in the 1930s with all the loose ends and unsolved problems. So it was a book that taught you everything that had been done in the '30s and made it absolutely clear that there was still a mess to be cleaned up, so it was a very good start for me to read this Heitler book. That's the one I remember the best. And it showed you the sorts of things which could be calculated. It had in it, amongst other things, Hans Bethe's calculation of the pair production which is a marvellous calculation. It had the classical, quantum and electrodynamics all there, and of course it was an introduction to the style of Hans Bethe - a lot of the stuff in Heitler's book, actually, is Bethe's work.