D O C U M E N T 5 F E B R U A R Y 1 9 1 9 7
hier sich ohnedies 3 Wochen hinausgezögert hat infolge „Heizferien“, die bis 20.
Mit herzlichen Grüssen Ihr
Herrn Anschütz meinen besten Dank für die
Es ist sehr erfreulich, dass uns Edgar Meier Ehrenhafts Versuche gewissenhaft
nachprüfen lässt. Die Ganzzahligkeit der Ladungsverhältnisse eines Teilchens ist
Ein anderer hiesiger Physiker hat den magneti-
schen Kreiseleffekt sorgfältigst nachgemessen; er findet nur die Hälfte des theore-
Hier wimmelt es von (hungrigen) Theoretikern. Abraham ist da,
Laue kommt bald her, auch Debye wollte
Alle freuen sich auf
AKS (GyMDM, Sommerfeld-Nachlass, 1977-28/A, 78(12)). Einstein/Sommerfeld 1968, pp. 55–56.
[21 393]. There is a perforation for a loose-leaf binder at the left margin of the document. The post-
card is addressed “Herrn Prof. Dr. A. Sommerfeld Leopoldstr. 87 München,” with return address
“Abs. A. Einstein Pension Sternwarte Zürich,” and postmarked “Zürich  Flu[ntern] 5.II.19.”
Date corrected on the basis of the postmark.
Arnold Sommerfeld (1868–1951) was Professor of Physics at the University of Munich and
director of its Institute of Theoretical Physics.
Einstein began teaching a 24-hour lecture cycle the previous week (see the preceding docu-
ment), thus delivering six hours per week prior to his return to Berlin before 23 February. Einstein
registered his residence at Hochstrasse 37 in Zurich on 27 January (see entry for this date in Calen-
Einstein arrived in Zurich at the beginning of January (see Doc. 1, note 2).
Hermann Anschütz-Kaempfe (1872–1931) was owner of a company in Kiel that produced
instruments for aerial and naval navigation, and a benefactor of Sommerfeld’s chair (see Eckert 1993,
pp. 65–67). Einstein made his acquaintance in 1918 when serving as an expert in one of Anschütz’s
patent cases (see Anschütz and Company to Einstein, 6 June 1918 [Vol. 8, Doc. 559], and Vol. 7,
Felix Ehrenhaft (1879–1952) was Extraordinary Professor of Physics at the University of
Vienna. From 1910 on he conducted experiments to determine the elementary electrical charge. In his
interpretation the results indicated that fractions of the electron (”subelectrons”) exist (see, e.g.,
Ehrenhaft 1910, the first of a series of publications on the same topic). Already in 1911, at the 1st
Solvay Conference, Einstein held that Ehrenhaft’s charge determination was not correct, referring to
Edmund Weiß’s calculations (see Vol. 3, Doc. 25, p. 509, and Einstein to Heinrich Zangger, 7 April
1911 [Vol. 5, Doc. 263], note 11). To test this controversial conclusion, Edgar Meyer (1879–1960),
Professor of Physics at the University of Zurich, bought Ehrenhaft’s experimental arrangement and
asked Richard Bär to repeat the experiments (see Felix Ehrenhaft to Einstein, 3 October 1918 [Vol. 8,
Doc. 630], and Edgar Meyer to Einstein, 20 October 1918 [Vol. 8, Doc. 637]). For their first results,
see Bär 1918a, 1918b, and 1919. For a historical discussion of Ehrenhaft’s work, see Holton 1978.
Two months later, Emil Beck (1881–1965), Professor of Mathematics at the Gymnasium of the
Zurich Kantonsschule, published his results in Beck 1919 (see Doc. 10). His experiment, as well as
work published by several other authors, seemed to indicate that a factor, later known as the gyromag-
netic factor g, entering into the theoretical explanation of the Einstein–De Haas effect had a value of
2 rather than 1, as had been expected (and found) by Einstein and Wander de Haas. For historical dis-
cusssions, see Vol. 6, the editorial note, “Einstein on Ampère’s Molecular Currents,” pp. 145–149,
and Galison 1987, pp. 58–60.
Max Abraham (1875–1922) was Professor of Physics at the Technical University of Munich;