D O C U M E N T 1 0 M A R C H 1 9 1 9 1 5
schaften des Originals hat. Herr Cohn wusste ganz genau, was sein Modell leistete
und was
nicht.[5]
Herr Petzold hat mich enttäuscht; er hat früher einmal besser über
die spezielle Relativitätstheorie
geschrieben.[6]
Ich halte den Wert solcher Modelle
nicht für sehr gross. Sie leisten nichts zur Erfassung des Grundgedankens, sondern
helfen nur dazu, die Verhältnisse im Einzelnen bequemer zu überschauen.
Beste Grüsse von Ihrem
A. Einstein.
ALS. [122 441]. Written on the verso of Scheel’s letter to Max Jakob, dated 20 March 1919.
[1]This letter is dated on the assumption that it was written the Monday before 20 March.
[2]Scheel (1866–1936) was director of the Physical-Technical Section of the Physikalisch-Techni-
sche Reichsanstalt (PTR) and secretary of the German Physical Society (Deutsche Physikalische
Gesellschaft, DPG).
[3]Professor Max Jakob (1879–1955) was a member of the PTR in Berlin. He sent a manuscript
with criticism of a recent paper (presumably by Petzoldt, see the following note) to Scheel, asking
him to forward it to Einstein for his opinion (see Karl Scheel to Max Jakob, 20 March 1919). Jakob
presumably submitted his manuscript to Scheel in the latter’s capacity as editor of the DPG Verhand-
lungen.
[4]Joseph Petzoldt (1862–1929) was Privatdozent for epistemology in the natural sciences at the
Technische Hochschule in Berlin. In Petzoldt 1918 he takes issue with a remark by Arnold Sommer-
feld to the effect that special relativity forbids one to conceive of space and time as something real. In
criticizing a Kantian interpretation of the concepts of space and time in special relativity, Petzoldt
argues for his own standpoint of positivistic realism. In this context he criticizes both Cohn 1918 and
Einstein’s popular book on relativity Einstein 1917a (Vol. 6, Doc. 42). Assuming that the manuscript
mentioned in the preceding note was subsequently published as Jakob 1919, it contains a critique of
Petzoldt 1918 as well as a defense of Cohn 1918.
[5]Emil Cohn (1854–1944) was Professor of Physics at the University of Strassburg. In Cohn 1918
he describes a mechanical model that is designed to illustrate the effects of length contraction and
time dilation. In his critique of Cohn, Petzoldt had argued that no mechanical model can ever faith-
fully illustrate time dilation because of the clock paradox.
[6]In a popular newspaper article of 1914 on the relativity principle, Einstein recommended both
Cohn 1913 (i.e., the first edition of Cohn 1918 mentioned above) and Petzoldt 1914 for detailed expo-
sitions of the philosophical and epistemological justification of special relativity (see Einstein 1914h
[Vol. 6, Doc. 1]). This recommendation was made even though Einstein had criticized Petzoldt for
misinterpreting the clock paradox (see Einstein to Joseph Petzoldt, 16 April 1914 [Vol. 8, Doc. 5]).
10. To Paul Ehrenfest
[Berlin,] 22. III. 19
Lieber
Ehrenfest![1]
So lange hab ich Scheusal nicht auf Deine herzerfreuende Einladung geantwor-
tet! Es war aber, weil ich nicht wusste, ob ich ja oder nein sagen sollte. Es zieht
mich nämlich mächtig zu Euch hin, aber andererseits ist das Reisen scheusslich,
besonders für einen mit wackeligen Gedärmen. (Es geht übrigens relativ sehr
gut).[2]
Auch Bohr würde ich gewaltig gern kennen lernen, diesen Menschen von