D O C U M E N T 4 2 3 J A N U A R Y 1 9 2 3 7 0 3
presence of matter and of the correct expression for the corresponding ponderomotive force had been
the subject of an earlier publication by Ishiwara (Ishiwara 1910a). Einstein had received a copy of
this paper, as well as of some others by Ishiwara, and had commented favorably on Ishiwara’s work
in Einstein to Jakob Laub, 4 November 1910 [Vol. 5, Doc. 231]): “Recently I received several papers
dealing with the theory of relativity from a Japanese […], among them one on ponderomotive forces.
In my opinion this is thus far the only paper written on this topic that makes sense. For substances
with constant μ and ε his results seem to me to be correct. But he too has (iB), so that his results can
hardly be valid for hard magnetic bodies (magnetic disk)” (“Neulich erhielt ich einige relativitätstheo-
retische Arbeiten von einem Japaner […], darunter eine über die ponderomotorischen Kräfte. Es ist
nach meiner Meinung die einzige bisher über diese Dinge geschriebene Arbeit, die Hand und Fuss
hat. Für Substanzen mit konstantem μ und ε scheinen mir seine Resultate richtig zu sein. Er hat aber
auch (iB), sodass seine Resultate für magnetische harte Körper kaum gültig sein dürften [magnetisier-
te Kreisscheibe].” Copies of Ishiwara 1910a, 1910b as well as of the later Ishiwara 1913 were in Ein-
stein’s offprint collection. The reference to the term (iB), where i is the conduction current, B the
magnetic induction, and the brackets denote the vectorial product, pertains to a controversy about the
correct expression for the ponderomotive force density on conduction currents in a magnetizable me-
dium in a magnetic field. While Minkowski’s—and Ishiwara’s—expressions had a term (iB), Einstein
and Laub argued for a term of the form (iH), with H denoting the magnetic force. For details about
this controversy, see Einstein’s joint publications with Laub in Vol. 2 and their correspondence in Vol.
5; see also Vol. 2, the editorial note, “Einstein and Laub on the Electrodynamics of Moving Media,”
pp. 503–507.
The problem also surfaces in Einstein’s Zurich notebook ([3 006], partially published as Doc. 10
in Vol. 4). There Einstein derived two alternative expressions for the ponderomotive force starting
from six-vector representations of the electromagnetic field tensor using four-dimensional vector al-
gebra, and commented on the result: “Two possibilities, one is the one by Ishiwara, but the other one
is the correct one” (“Zwei Möglichkeiten, eine ist die von Ishiwara, die andere aber ist die zutref-
fende”; see also Renn 2007; vol. 1, pp. 327, 329).
[2]The correct second term is (see Doc. 433).
423. From Sergei F. von Oldenburg[1]
[Petrograd, 18 January
1923][2]
Übersetzung
Hochgeehrter Herr Kollege
Die Akademie der Wissenschaften von Russland hat in Ihrer Sitzung vom 29
December Sie zum Correspondierenden Mitgliede der Akademie gewählt, als ein
Zeichen ihrer hohen Achtung zu Ihren so ausserordentlich werthvollen wissen-
schaftlichen Arbeiten.
Das betreffende Diplom wird Ihnen gleich nach Verfertigung zugeschickt
werden.
Hochachtungsvoll
S. von Oldenburg
Beständiger Sekretär
ρuμ
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