310 DOC. 23 ELECTRODYNAMICS OF MOVING BODIES
dargetan
wurde. Es ist vielmehr
zweckmäßig,
die Kraft
so zu
definieren,
daß
der
Impulssatz
und
der
Energiesatz
die einfachste Form anneh-
men")
(Blumenthal 1913,
p.
51;
for
Planck's
definition,
see
Planck
1906a).
Einstein
adopted
Planck's
definition in Einstein
1907j
(Doc. 47).
[42]
Abraham
(Abraham
1902a,
1902b, 1903);
Lorentz
(Lorentz
1904a);
and Bucherer
(Buch-
erer
1904,
pp.
57-58;
see
also
Langevin
1905c)
had
proposed
models
of
the electron that
re-
sulted in
differing equations
of
motion. For
a
contemporary review,
including an
account of
relevant
experimental
results,
see
Bucherer
1904,
pp.
51-68.
[43]
The term after the second
equality
sign
should include
a
factor
u.
[44]
Einstein returned to the
question
of
the im-
possibility
of
superluminal
velocities in Einstein
1907h
(Doc. 45), pp.
381-382.
For
a
discussion
of
his
correspondence on
this
question a
few
years later, see
Vol.
5,
the editorial
note,
"Ein-
stein
on
Superluminal
Signal
Velocities."
[45]
See
Einstein
1907j (Doc. 47),
p.
437,
for
precise
definitions and further discussion
of
Am
and
Ae.
[46]
See
Einstein
1907j
(Doc. 47),
pp.
436-
437, for
a
similar discussion
of
these three rela-
tionships,
but which avoids the
concepts
of
transverse and
longitudinal
mass.
[47]
In
a
lecture
given
in 1922 at
Kyoto
Uni-
versity,
Einstein mentioned
an important
discus-
sion with
a
friend,
presumably
Michele
Besso,
reviewing
Einstein's
difficulties with the elec-
trodynamics
of
moving
bodies
(see
Ishiwara
1971 for
an
account
of
this
lecture).
For the
ex-
cerpt alluding
to
Besso's
role,
see
the editorial
note,
"Einstein
on
the
Theory
of
Relativity,"
p.
264. See
note
27 for
Besso's
suggestion
of
an-
other
possible
contribution he made to the
paper.