It is now a little more than 11 years since the idea of writing a personal and scientific biography of H. A. Kramers took hold of me. A few days earlier I had been lecturing, in a course on field theory, on the renormalization proce­ dures of relativistic quantum field theory. Since the students had considerable trouble understanding the physical basis of the procedure, at the end of the lecture T explained that renormalization is not an exclusive quantum or relativistic procedure. A careful treatment of classical electron theory as started by Lorentz and developed in detail by Kramers also requires re­ normalization. The students appeared quite interested and I promised them that I would explain all this in more detail in the next lecture. I could have looked up this material in Kramers' book, but I remembered that Kramers had stressed this idea in a course I had attended in Leiden in 1938-1939. I did dig up some of these old notes and, although they were considerably less transparent than my recollection seemed to indicate, they reminded me force­ fully of the thrilling days I had spent in Leiden with Kramers. Kramers' deep insight and originality were apparent even when distorted by my opaque notes. The students had never heard of these ideas of Kramers' and were totally unaware of his work in field theory.

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