DOC. 47 THE RELATIVITY PRINCIPLE
485
Published in
Jahrbuch der Radioaktivität
und
Elektronik
4
(1907):
411462.
Received 4 De
cember
1907, published
22
January
1908.
[1]
Lorentz 1895.
[2]
See Lorentz
1895,
§
V.
[3]
Michelson
and
Morley
1887,
which
gives
the results
of
a more
precise
repetition
of
the
ex
periment reported
in Michelson 1881. This
is
Einstein's first
known reference to
the Michel
sonMorley experiment.
[4]
See
FitzGerald
1889
and Lorentz
1892b.
[5]
This
may
be
an
allusion
to attempts to set
up an
emission
theory
of
light.
For
evidence
of
an
attempt
by
Einstein before
1905,
see
the edi
torial
note,
"Einstein
on
the
Theory
of
Relativ
ity,"
pp.
263264.
[6]
Lorentz
1895,
pp.
4950, defines the local
time
t' for
a
frame
of
reference
moving through
the
ether
by
the
equation:
t'
=
t

px/V2
x

py/V2
y

pz/V2
z,
where
t
is the
(universal) time, p is
the
velocity
vector
of
the
moving
frame with
respect
to
the
ether
frame,
and
r
=
(x,y,z)
is the
position vec
tor with
respect
to the ether frame
of
the
point
at
which the local time is calculated. Lorentz
1904a defines the local time
by an
expression
that is
formally equivalent to
Einstein's
expres
sion for the time relative
to
the
moving
frame
of
reference. Cohn
1904b,
p.
1408,
expresses
a
view similar
to
Einstein's
on
the role
of
the local
time.
[7]
See Einstein 1905s
(Doc. 24),
Einstein
1906e
(Doc. 35),
and Einstein 1907h
(Doc. 45)
for discussions
of
the inertia
of
electromagnetic
energy.
[8]
See Cohn
1900, 1902, 1904a,
1904b.
A
copy
of
Cohn 1904a
is
in
Einstein's
collection
of
reprints, now
in IsReW.
[9]
Lorentz 1904a and Einstein 1905r
(Doc.
23) (the
reference should be
to
vol.
17).
[10]
Laue
1907. A
reprint copy,
dedicated
"To
the
discoverer of
the
relativity principle"
("Dem
Entdecker
des Relativitätsprinzips"),
containing a
short calculation
in Einstein's
hand,
is
in
Einstein's
collection
of
reprints, now
in
IsReW.
[11]
Laub
1907
(the
reference should be
to
vol.
23).
In
a
letter
of
4
September
1907,
Max Laue
informed Einstein that he had discovered
Laub's
paper
after
completing
work
on
Laue
1907.
Since
Laub's
paper
contains several
errors,
Laue
decided not to
withdraw his
paper,
but to inform
Laub
of
his
objections.
[12]
See Einstein 1905r
(Doc.
23),
pp.
917
920.
[13]
Planck
1906a.
Planck
1907a,
cited below
by
Einstein in connection
with this
topic,
is
Planck's
second
paper
on
the
topic.
[14]
Einstein
1905s
(Doc. 24),
1907h
(Doc.
45),
and
Planck
1907a.
[15]
Mosengeil
1907. The
article,
based
on
Mosengeil's
1906 Berlin doctoral
thesis,
was
prepared
for
publication by
Planck,
his thesis
su
pervisor,
after
Mosengeil's
death
(see
ibid.,
p.
867).
[16]
The
question
of
rigid
bodies in the
theory
of
relativity was an
unsolved
problem
at
this
time
(see
Einstein 1907h
[Doc. 45],
§
3).
Ein
stein here noted that
only rigid
motions
of
solid
bodies
are required.
[17]
Lorentz
1895.
[18]
See
Fizeau 1851. For
Lorentz's
explana
tion
of
the
dragging
coefficient,
see
Lorentz
1895,
pp.
9699.
[19]
See
note
3.
[20]
Einstein here introduced the
terms "geo
metrische
Gestalt"
and
"kinematische Gestalt"
to
generalize
what he had earlier called
"the
length
of
the
rod"
("die
Länge
des Stabes") and
"the
length
of
the
(moving)
rod in
a
system at
rest"
("die
Länge
des
(bewegten)
Stabes
im
ru
henden
System"), respectively (see
Einstein
1905r
[Doc. 23], p. 896).
[21]
The derivation
of
the transformation
equa
tions
given
in this section differs
substantially
from that
given
in Einstein
1905r
(Doc. 23),
§3.
[22]
This rule had been
given
in
Planck
1907a,
p.
551.
[23]
Stark
1906.
[24]
Einstein discussed this
question
in
more
detail in Einstein 1907e
(Doc. 41).
[25]
The "n'x
"
in the
denominator
should be
"u'x."
[26]
The
c
in the denominator of the last
term
should
not
be
squared.
[27]
The discussion in the remainder
of
this
paragraph
follows Einstein 1907h
(Doc. 45), pp.
381382.
[28] The
"X"
should be
"l."
[29]
The
topics
that
are
treated
kinematically
in
this section
are
not discussed in Einstein 1905r
(Doc.
23)
until after the introduction
of
Max
well's
equations
(see
ibid.,
pp.
910911).
[30]
The
"x"
in the
numerator
should be
"x'."
[31]
The
wording
of
this
paragraph
is
almost