2026-10-09 Max Planck Research Library (MPRL) and Eckert's history papers
Found via Google query Sommerfeld "Atombau und Spektrallinien" 1922 third edition archive.org. Scripted downloads.
Eckert, "Sommerfeld's Atombau und Spektrallinien" (chapter 6 in Badino and Navarro, eds., Research and Pedagogy: A History of Quantum Physics through Its Textbooks, MPRL Studies 2, Edition Open Access 2013, CC BY-NC-SA)
https://www.mprl-series.mpg.de/studies/2/7/index.html ; PDF saved as files/Eckert-MPRL-Studies2-ch6-Atombau.pdf. (The PDF text layer uses a shifted font encoding; decoded copy in research/pages/, digits lost.) Michael Eckert is at the Deutsches Museum, which holds Sommerfeld's papers. - The third edition (the one translated in the project folder) was widely praised; Hermann Weyl wrote "Your book is now my physical bible"; Planck: "Everywhere one becomes aware about the progress" [web, Eckert's translations of letters]. - "Within less than a year more than four thousand copies were sold"; "the third edition was translated into English and French"; physicists abroad used the German edition meanwhile; the English translation made from the third edition appeared in America around the time of Sommerfeld's 1922-23 US visit (Madison, C. E. Mendenhall) [web]. - Eckert describes the "doublet riddle" (Forman 1969): X-ray doublets explained relativistically, optical doublets magnetically; in April 1924 Millikan's ultraviolet spectra suggested both were relativistic; Sommerfeld to Landé: "The relativity formula far from being obsolete or refuted extends its validity into the optical realm", meant as an abdication of model explanations, not a victory of one model [web]. Bears on claims 5 and 7. - The book was written with students (Pauli, Heisenberg) involved in writing and proof-reading; the first edition (1919) began as popularisation [web].
Eckert, "How Sommerfeld extended Bohr's model of the atom (1913-1916)", Eur. Phys. J. H 39, 141-156 (2014)
Author copy https://commons.princeton.edu/josephhenry/wp-content/uploads/sites/71/2021/01/How-Sommerfeld.pdf ; saved files/Eckert-How-Sommerfeld-extended-Bohrs-model.pdf. - The extension was driven by the Zeeman and Stark effects (Stark's Oct 1914 hydrogen results). Sommerfeld specified one constant only "from hindsight in an appendix" [Sommerfeld 1916a, p.499]; the uncertainty was resolved later by Schwarzschild [web, Eckert p.~150]. - Paschen photographed "H alpha und H beta as double lines" but doubted they were satisfactory while it was unclear "whether the duplicity could not be due to some known or unknown effects (Stark effect, for example, as Bohr assumes it as possible)" (Paschen to Sommerfeld 12 Dec 1915). He at first followed Bohr's view that the He+ structure came from a Stark effect of the nucleus; Sommerfeld doubted this and asked for a closer check; Paschen: "So the discrepancy is theoretically required! There is nothing like a fine theory!" [web]. Sources: DMA HS 1977-28/A,253; "Also in ASWB I" (the printed letter edition). - "For the problems with the hydrogen fine-structure see [Robotti 1986]" — Robotti, N. (1986), "The hydrogen spectroscopy..." (title truncated in the Google snippet of Vickers's paper; not obtained). - Wilhelm Lenz, writing from the Western Front (7 Mar 1916), derived the closed relativistic energy formula himself ("Because this law was not explicitly presented in your paper I have derived it myself") [web]. Lenz is also the source of the Abraham-vs-Einstein test (see Glitscher 1917 in the archive.org note). - Paschen 21 May 1916 (quoted by Eckert and Kragh): "My measurements are now finished and are in wonderful agreement with your fine structures" [web].