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2026-10-09 Sommerfeld-Projekt (LMU Munich) letter database

Site: https://sommerfeld.userweb.mwn.de/ (Lehrstuhl für Geschichte der Naturwissenschaften, LMU; DFG project 1995-2000; data "ausgelesen am 07. März 2004"). Online index of Sommerfeld's scientific correspondence: per-person letter lists, a short German summary (Kurzfassung) for each letter with its archive location, and for some letters a full transcription. Accessed by script (curl); no login.

Searches: person index pages P (Paschen, id 00136), G (Gehrcke 00544, Glitscher 01311), B (Brose 02220); subject index F (no "Feinstruktur" subject heading exists). Letter summaries fetched for all Gehrcke-indexed letters and the Paschen letters of Dec 1915; two transcriptions read in full (TransDat/02183, TransDat/00585).

Bearing on the project: priority 1 (the inventor's own words outside the book) and priority 4 (historical record). The book (3rd German ed., preface Jan 1922; English 1923) states the fine-structure case publicly; these letters show what Sommerfeld and Paschen said privately before and after.

Findings

  1. Sommerfeld privately doubted the size of the predicted hydrogen doublet, 1924. Sommerfeld to Paschen, 23 May 1924 (DM Archiv NL 89, 003), transcription https://sommerfeld.userweb.mwn.de/TransDat/02183.html [web]. Asked his opinion on the "Relativitätsdublett", he writes that he is convinced the relativistic theory is right, "sie wird durch die Anzahl und Lage der Komponenten sichergestellt" (secured by the number and position of the components), "Aber die Grösse von [Delta nu] = 0,365 möchte ich nicht mit gleicher Sicherheit behaupten." He gives a reason: the mass formula was derived only for the isolated electron, whereas in the atom there is interaction with the nucleus; a mutual mass ("Trägheit der potentiellen Energie") could give a weaker velocity dependence and so a smaller doublet. He continues: "Die Möglichkeit Abraham an Stelle von Einstein zu setzen, ist natürlich indiscutabel und entspringt dem fanatischen Geist der Lenard, Gehrke, Lau." But he says he was made "sehr nachdenklich" by Lau's demonstration that for the higher analogues of He+ 4686, where the ideal triplet should come out ever purer, the Delta nu values stay noticeably smaller while their ratio becomes very exactly 1:3 (citing "den Bericht von Lau S. 65"). He dismisses McLennan's "brilliant confirmation" of the Delta nu value as meaning little given its known unreliability, and urges Paschen to get new, more exact values of the fine-structure constant: "Die Theorie dazu werden wir schon nachliefern." He also remarks that Landé's polemic against the relativistic reading of X-ray doublets seems to end in a huge widening of the relativistic formula's range, "ebenso unverständlich im sichtbaren wie im Röntgengebiet". - Bears on claim 2 (the 0.27-0.33 vs 0.365 cm^-1 shortfall that the book calls "partly explained") and claim 6 (the Abraham-electron "experimentum crucis" and the constants derived from the doublet). The book presents 0.365 and the relativity test with confidence; two years later the author privately separates the structure (secure) from the absolute size (not secure) and names the dissenters.
  2. Sommerfeld to Paschen, 29 Dec 1915 (DM HS 1977-28/A,253; "u.U. nur Briefentwurf"), transcription https://sommerfeld.userweb.mwn.de/TransDat/00585.html [web]. Before the full theory was published, Sommerfeld compares Paschen's hydrogen Balmer-line differences 0.16 : 0.24 : 0.26 (ratio 1 : 1.5 : 1.62) with his theory's 7/16 : 16/25 : 27/36 = 1 : 1.46 : 1.73 ("Das stimmt vortrefflich"), but adds "Dagegen stimmen die Absolutwerte nicht": his formula gives 0.102 where Paschen finds 0.24; he tries a factor 5 in the correction term. The struck-out lower half (transcribed by Frau Bodenmüller) contains a hydrogen doublet estimate Delta nu_H = 0.715 and the ratio 0.715/0.31 = 2.3. This is a working draft from the period when the theory was still being fixed; it records an absolute-value mismatch at the start of the Paschen collaboration.
  3. Paschen to Sommerfeld, 27 Dec 1915 (summary, KurzFass/00584) [web]: Paschen answers questions on the hydrogen fine structure, suspects influence of the Stark effect, asks how Sommerfeld's theory differs from Bohr's. 30 Dec 1915 (KurzFass/01573): new helium measurements; Paschen is glad the "Unstimmigkeit" is theoretically required: "Es geht doch nichts über eine feine Theorie!" Both are printed in Band 1 of the Sommerfeld edition (Eckert and Märker, 2000).
  4. Sommerfeld to Schwarzschild, 28 Dec 1915 (Göttingen NSUB, Schwarzschild 743; summary KurzFass/00167) [web]: he lectured on Einstein's general relativity in the summer semester, reports Einstein's euphoria over the Mercury perihelion, is working "mit Volldampf" on spectral lines and outlines the fine-structure splitting.
  5. The anti-relativity controversy in the letters (summaries only) [web]: Scheel to Sommerfeld 14 and 24 Jan 1920 (controversy and "Schwierigkeiten mit Gehrcke, Lenard u.a." at the new Zeitschrift für Physik); Laue to Sommerfeld 25 Aug 1920 (the Berlin anti-relativists around Weyland; asks Sommerfeld as DPG chairman for a counter-resolution at Bad Nauheim); Sommerfeld to Einstein 3 Sep 1920 (indignation at the "Hetze" against Einstein); Volkmann to Sommerfeld 16 Jan 1925 (asks Sommerfeld to look over Gehrcke's writings against relativity for an Annalen review) and Sommerfeld's reply 20 Jan 1925 (advises restraint).
  6. Later fine-structure measurements in the letters (summaries only) [web]: Ornstein to Sommerfeld 7 Apr 1925 (van Cittert's work interpreting hydrogen fine-structure experiments); Gerhard Hansen to Sommerfeld 23 Jul 1925 ("Hansen kritisiert die Experimente von Houston zur Messung der Feinstruktur").
  7. Sommerfeld to Landé, 20 Apr 1924 (SBPK Nachlass Landé) [web]: "Wir haben in der letzten Zeit wiederholt erfahren, dass die arithmetischen Regelmässigkeiten viel weiter reichen als nach den Modellvorstellungen zu erwarten wäre." Bears on claim 7 (the book's own statement that series regularities are "mainly empirical").
  8. Brose (translator) letters [web]: Henry Leopold Brose (1890-1965) appears in letters of 10 Apr and 8 Oct 1922 (Sommerfeld to his wife) and later business letters (Vieweg 1933, 1939; Methuen 17 Jun 1939). Not read; they may document the translation of the edition in the project folder.
  9. Glitscher [web]: letters 1915-1942 index him; the dissertation itself was found on archive.org (see that note).

Not reached: full letter lists for 1916-1922 under Paschen (the page lists more than shown); the Wissenschaft (subject) index under R (Relativitätstheorie) and S (Spektrallinien).