4 7 2 D O C U M E N T 3 4 8 M A R C H 1 9 2 0
[11]Einstein considered Paul Epstein’s prospects for a position at the University of Zurich as very
tenuous (see the Doc. 335).
[12]Ehrenfest first mentioned the possibility of an Assistent position for Epstein in Doc. 239.
[13]Epstein was born in Warsaw, Poland (at the time part of Russia), and received his Master’s
degree at the Imperial University of Moscow. He presumably hoped for an eventual position in
[14]Grebe and Bachem 1920 was published in the Zeitschrift für Physik, the journal newly founded
by the German Physical Society. Einstein informed Ehrenfest of the merger of two earlier journals
(without mentioning the new title) in Doc. 254, and drew Ehrenfest’s attention to the paper by Grebe
and Bachem in Doc. 335.
[15]Leonhard Grebe; Willem H. Julius.
[16]At this point in the original text Ehrenfest indicates a note that he appended at the right margin
of the document: “Fortsetz Rückseite !!!”
[17]Einstein, admitting the existence of strongly perturbing effects, expressed his conviction that
these can be distinguished from the effect of gravitation in Doc. 208. On Julius’s theory of dispersion,
see Doc. 192, note 2.
[18]Viktor Trkal (1888–1956) was a research student and Assistent at the University of Leyden. The
results were communicated to the Royal Academy of Sciences in Amsterdam on 28 February 1920,
published as Ehrenfest and Trkal 1919–20 and, with minor modifications, as Ehrenfest and Trkal
1921. See Klein, M. 1959, for a historical discussion.
The term “chemical constant” refers both to the integration constant that Walther Nernst found
when integrating the Clausius–Clapeyron equation, and to the entropy constant, which differs from
the previous one by an additive term. The “theory of chemical constants” stands for early quantum
theory of the perfect gas.
[19]The division by N! was introduced in the definition of thermodynamic probability in Sackur
1912. For the connection of the problem with the distinguishability of particles and for the reception
of Ehrenfest and Trkal’s procedure, see Desalvo 1992.
Nernst’s theorem is the third law of thermodynamics.
Otto Stern calculated the chemical constant by considering the solid-vapor equilibrium; see, e.g.,
his review paper, Stern, O. 1919.
Ludwig Boltzmann used a mechanical model in his calculations of gas dissociation, namely that
of “sensitive domain” (“empfindlicher Bezirk”), a “bulge” on the surface of the atom or of a sphere
around it. Chemical bonding takes place when sensitive domains touch each other or overlap
(Boltzmann 1898, pp. 177–191). In Ehrenfest and Trkal’s quantum version of the theory of dissocia-
tion, the individual atoms are taken into account even for nondissociated molecules. Combinatorial
arguments, as well as the introduction of a weight in phase space proportional to h, then lead to ex-
pressions for the chemical constant.
[20]At this point in the original text Ehrenfest indicates a note that he appended at the right margin
of the document: “Fortsetz Seite !!!”
[21]The secretary was Ilse Einstein. The appended questions are not extant.
[22]Violins for Tatiana and Anna Ehrenfest (see Doc. 335).
[23]A nickname for elder daughter, Tatiana.
348. From Ludwik Silberstein
London, N. W. 2. 4, Anson Road Den 10. März, 1920.
Sehr geehrter Herr Professor!
Aus Dr. A. Berliner’s (“Die Naturwissenschaften) Brief, den mir heute Laue zu-
schickt, erfahre ich dass Sie gegenwärtig sich in Berlin
Ich erlaube mir deshalb unter dieser Adresse Ihnen ein Paar Zeilen zu schreiben
und, beiliegend, ein Separatum aus dem Phil. Mag, üb. den “Stokes-Planckschen
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