DOC. 23 ELECTRODYNAMICS OF MOVING BODIES 307
[3]
Einstein
is
presumably referring
to the
proof
in
Lorentz
1895, pp.
91-95.
In the 1913
reprint
of
this
paper,
a
note
was
added
after
"Ordnung":
"The
preceding paper by
H. A.
Lorentz
[a
German translation
of
Lorentz
1904a]
was
not
yet
known to the
author"
("Die im Vor-
hergehenden abgedruckte
Arbeit
von
H. A. Lo-
rentz
war
dem Verfasser noch nicht bekannt")
(Blumenthal 1913,
p.
27).
Einstein later stated
that in 1905 he knew
"only
Lorentz's
important
1895
work,
but not
Lorentz's
later
work"
("nur
Lorentz bedeutendes Werk
von
1895,
aber nicht
Lorentz'
spätere
Arbeit")
(Einstein
to Carl See-
lig,
19
February
1955).
In this
paper,
Einstein's
notation for the
velocity
of
light
and
many
other
quantities agrees
with that used in Lorentz 1895.
[4]
Einstein
encountered the
"principle
of
rel-
ative
motions"
("Prinzip
der
relativen Bewe-
gungen")
a
decade earlier in Violle 1892
(see
the editorial
note,
"Einstein
on
the
Theory
of
Relativity,"
pp.
258-259). More
recently (see
note
2),
he had read
Poincare
1902,
which dis-
cusses
"the
principle
of
relative movement"
("le
principe
du mouvement relatif")
on
pp.
135-137
(see
note 12 for
Poincare's
definition
of
this
principle).
In
discussing
whether Lorentz's
theory
contradicts the
principle,
Poincare used
the
phrase
"le
principe
de
relativite"
(ibid.,
p.
281),
translated into German
as
"das
Prinzip
der
Relativität"
(Poincare 1904a,
p.
243).
There
is
a more
extensive discussion
of
the
principle
and
its relation to
Lorentz's
theory
in
Poincare
1904b,
pp.
310-312.
Abraham/Föppl 1904
mentions the
"principle
of
relative
motion"
("Prinzip
der relativen Bewegung")
on
p.
398.
[5]
See
pp.
900-901 for
Einstein's
proof that
this
assumption
is consistent with the
relativity
principle.
In
1904,
Wien and Abraham stressed
the
importance
of
the
constancy
of
the
velocity
of
light
in
electrodynamics.
Wien
rejected
Cohn's
electrodynamics
of
moving
media
(see
Cohn
1902)
because
it
violates
"the
constancy
of
the velocity
of
light
and hence the foundations
of Maxwell's
theory....
For,
once
it
has left
the
radiation
source,
it
should not affect the
ve-
locity
of
propagation
of
radiation whether the
source
has
moved
or
not"
("die Konstanz
der
Lichtgeschwindigkeit und
damit die
Grundlagen
der
Maxwellschen
Theorie....
Denn
es
muß
für die
Fortpflanzungsgeschwindigkeit
einer ein-
mal
von
der
Strahlungsquelle
losgelösten
Strah-
lung gleichgültig
sein,
ob sich diese
bewegt
hat
oder
nicht"
(Wien 1904, p. 643).
Abraham
stated:
"The
electromagnetic theory
of
light re-
fers
to
an
absolute motion
of
light,
which
pro-
ceeds in
every
direction with the
same velocity
(c)" ("Die
elektromagnetische
Lichttheorie
spricht von
einer absoluten
Bewegung
des
Lichtes, die nach
jeder
Richtung
hin mit dersel-
ben
Geschwindigkeit (c) erfolgt") (Abraham
1904b,
p.
238).
[6]
See the editorial
note,
"Einstein
on
the
Theory
of
Relativity,"
pp.
260-261,
for
Ein-
stein's
reading
of
books
by
Mill, Ostwald,
and
Poincare that
question
the existence
of
the ether.
In the
years just
prior to 1905,
several
physicists
suggested
the elimination
of
the
ether
from elec-
trodynamics.
Bucherer cited evidence that
opti-
cal
phenomena
only depend on
the relative
mo-
tion
of
matter
with
respect
to
other
matter (see
Bucherer
1903,
p.
282;
Bucherer
1904,
pp.
128,
130-131). Cohn noted there
is
no
need to intro-
duce
an
ether
in his
theory;
it suffices to
assume
that
electromagnetic energy can propagate
in
matter-free
space
(see
Cohn
1902,
p.
55).
[7]
Einstein
is
evidently
contrasting
his
ap-
proach
to
the
electrodynamics
of
moving
bodies
with those
of
Lorentz and
Hertz,
respectively.
For earlier
comments
on
Hertz's
electrodynam-
ics,
see
Einstein to Mileva Maric,
10
August
1899
(Vol.
1,
Doc.
52).
For later comments
on
Lorentz and
Hertz, see,
e.g., Einstein
1910a,
pp.
7-10, and Einstein
1921a,
p.
782.
[8]
In the 1913
reprint, a
note
was
added after
"gelten": "What
is
meant
is,
'be
valid in the
first
approximation'
")
("Gemeint
ist: "in
ers-
ter Annäherung
gelten"
")
(Blumenthal 1913,
p. 28).
The
authorship
of these
unsigned
addi-
tional
notes
is unclear
(see
McCausland
1984).
The
title
page
of
Blumenthal
1913
says
"A
Col-
lection
of
Papers
with Annotations
by
A. Som-
merfeld"
("Eine
Sammlung von Abhandlungen
mit
Anmerkungen von
A. Sommerfeld"). How-
ever,
the extensive notes
by
Sommerfeld
on
Minkowski
1909,
printed
after the
reprint
of
that
paper,
are
listed
separately,
under
Sommerfeld's
name,
in the table
of
contents. Lorentz
signed
a
note
he
added to
the
German translation
of
Lo-
rentz
1904a.
If
Einstein
did not write
the
addi-
tional
notes to
this
paper,
the
contents
of
some
suggest
that he
was
consulted.
[9]
Poincare
1902,
p.
111,
states:
"Not
only
do
we
not have
a
direct intuition
of
the
equality
of
two time
intervals,
but
we
do
not
even
have
that
of
the
simultaneity
of
two events that
are
produced
at different
localities;
I have
explained