1. Kramers’ visit to Göttingen is confirmed by a letter of Born. He remarked: ‘Kramers was here for eight days’ (Born to Einstein, 15 July 1925).
2. In Heisenberg’s paper the introduction formed one paragraph. B. L. van der Waerden split it in his translation, beginning the second paragraph at this point (van der Waerden, 1967, p. 261).
3. See, e.g., Niels Bohr’s statements in his review article on atomic structure (Bohr, 1923c, p. 228).
4. See Kramers and Heisenberg, 1925, p. 683, Eq. (5). The factor 2 stemming from the two modes of polarization was not included in the Kramers-Heisenberg formula.