D O C U M E N T 4 8 F E B R U A R Y 1 9 2 1 8 3
to segregate thermal radiation by frequency, and therefore temperature (in violation of the second law
of thermodynamics).
[7]Einstein had described this proposed experiment in Doc. 37. For Born’s later reflections on this
proposal, see Einstein and Born 2005, p. 49.
[8]In Doc. 37, Einstein had drawn Born’s attention to a paper by Alfred Byk, Byk 1921a. Otto Stern
(1888–1969) was Extraordinary Professor at the University of Frankfurt.
[9]Erwin Madelung (1881–1972), Professor of Theoretical Physics at the University of Münster,
was appointed as Born’s successor in Frankfurt (see Physikalische Zeitschrift 22 (1921): 160).
[10]On Born’s attempts to get Stern appointed as his successor, see Max Born to Einstein, 8 Decem-
ber 1920 (Vol. 10, Doc. 224).
[11]Niels Bohr had been invited in November 1920 by the Wolfskehl Foundation to lecture in Göt-
tingen in June 1921. However, due to Bohr’s ill health, the visit was eventually postponed until June
1922 (see Mehra and Rechenberg 1982, p. 344).
[12]Born’s attempts to measure the elasticity constants of diamond did not succeed (see Einstein
and Born 2005, p. 53).
[13]Otto Heinrich Wiener (1862–1927) was Professor of Physics at the University of Leipzig. He
was a pioneer of color photography, and did work on crystallography and polarization of light. Born
made use of a Carl Zeiss microinterferometer for these experiments (see Einstein and Born 2005,
p. 53).
[14]Woldemar Voigt (1850–1919) had been Professor of Physics at the University of Göttingen and
was well known for his work on the physics of crystals.
[15]Paul Oppenheim (1885–1955) was a chemist with N. M. Oppenheim Nachfolger.
[16]Born 1921a.
[17]Constantin Carathéodory (1873–1950) was Professor of Mathematics at the University of
Smyrna. For his work on the foundations of thermodynamics, see Carathéodory 1909.
[18]Born 1921c; see also Born 1923a, pp. 730–733.
[19]A second edition of Born 1915 appeared both as Born 1923a and as a contribution to the Ency-
clopedia of the Mathematical Sciences (Born 1923b). Imre Bródy (1891–1944), Assistent at the Uni-
versity of Göttingen, was a native of Hungary.
[20]Bródy 1921.
[21]Walther Gerlach (1889–1979) was Extraordinary Professor of Physics at the University of
Frankfurt.
[22]On James Franck’s call to Göttingen, see Max Born to Einstein, 16 July 1920 (Vol. 10, Doc. 75).
[23]From Carl Still, an industrialist in Recklinghausen (see Einstein and Born 2005, p. 53).
[24]Wilhelm Wien (1864–1928) was Professor of Physics at the University of Munich.
[25]Born 1920.
[26]Wolfgang Pauli (1900–1958) was a student at the University of Munich (see Doc. 98). His arti-
cle, Pauli 1921, consists of 237 pages.
[27]For Einstein’s views on the question of German reparations, see Doc. 37.
48. To Paul Ehrenfest
Berlin Sonntag Abend. [13 February
1921][1]
Lieber Ehrenfest!
Einer abenteuerlichen politischen Idee wegen hab ich rasch mit einigen Genos-
sen nach Amsterdam fahren
müssen,[2]
habe aber nicht Zeit, Euch zu
besuchen.[3]
Die Schritte für die russischen Kollegen habe ich damals unmittelbar nach