THEORY OF RELATIVITY 259
ics
on
the
"principle
of
relative
motions"
("Prinzip
der relativen
Bewegungen") together
with the
principle
of
inertia.[32]
About
1898,
Einstein started
to
study
Maxwell's
electromagnetic
theory, apparently
with the
help
of Drude's
textbook.[33]
By
1899,
after
studying
Hertz's
papers on
the sub-
ject,
he
was
at work
on
the
electrodynamics
of
moving
bodies.[34]
He
discussed
this
topic
a
number
of
times in letters to Mileva Maric between 1899 and
1901,[35] once referring
to
"our
work
on
relative
motion"
("unsere Arbeit über die
Relativbewegung").[36]
In De-
cember
1901,
Einstein also
explained
his ideas
on
the
subject
to
Professor
Alfred
Kleiner
of
the
University
of
Zurich,
who
encouraged
him to
publish them;[37]
but there
is
no
evi-
dence that
Kleiner
played
a
further role
in
the
development
of
these ideas.
Einstein's
comments show that in 1899 his
viewpoint on electrodynamics was
similar
to that
of
Lorentz;[38]
but, aside from this
similarity,
there
is
no
evidence that Einstein had
yet
read
anything by
Lorentz.[39]
Shortly
afterward,
Einstein
designed an
experiment
to
test the effect
of
the motion
of
bodies relative to the ether
on
the
propagation
of
light;
in
1901
he
designed a
second such
experiment,
but
was
unable
to
carry
out
either.[40]
Near
the
end
of
1901,
he
was
at work
on
what he described
as
"a
capital
paper"
("eine
kapitale
Abhandlung") on
the
electrodynamics
of
moving bodies,
asserting
his renewed conviction
of
the correctness
of
his
"ideas
on
relative motion"
("Ideen über die Relativbewe-
gung").[41]
His words
may
indicate that he
already
doubted whether motion with
respect
to the ether
is
experimentally
detectable.[42] Soon afterward he wrote that he intended to
study
Lorentz's
theory
in earnest.[43]
[32]
See Violle
1892, pp.
90-91, for the state-
ment
of
the two
principles,
and
pp.
92-94 for the
derivation
of Newton's
second
law
(see p.
90 for
Violle's
discussion
of
the
role
of
such
principles
in
physics).
A
copy
of
Violle
1892
is
in Ein-
stein's
personal
library.
A
marginal
annotation
in
Einstein's hand
on p.
94 indicates that he read
this section
of
the
book.
[33]
Drude 1894.
For
evidence that Einstein
read
Drude,
see
Einstein
to
Mileva
Maric, 16
April-8
November 1898 and after
16
April
1898
(Vol.
1,
Docs. 40 and 41),
especially
the
de-
scriptive
notes
to
both letters.
[34]
Hertz,
H.
1890a, 1890b. For
Einstein's
discussion
of Hertz's
work, see
Einstein
to
Mi-
leva
Maric,
10
August
1899
(Vol. 1,
Doc.
52).
[35]
See Vol.
1,
the editorial
note,
"Einstein
on
the
Electrodynamics
of
Moving
Bodies,"
pp.
223-225,
for
a
list and discussion
of
these let-
ters.
[36]
Einstein to Mileva Maric, 27 March
1901
(Vol.
1,
Doc.
94).
There
is
no
indication in their
letters
of
the nature
of
her
collaboration,
if
any,
in his research.
[37]
See Einstein to Mileva Maric,
19
Decem-
ber
1901
(Vol.
1,
Doc.
130).
[38]
See Einstein to Mileva
Maric, 10
August
1899
(Vol.
1,
Doc.
52).
[39]
Einstein
may
have
already
read Wien
1898,
which includes
a
review
of Lorentz's
the-
ory.
For evidence that Einstein read this
article,
see
Einstein
to
Mileva
Maric,
28
September
1899
(Vol.
1,
Doc.
57).
[40]
See Einstein
to
Mileva
Maric, 10
Septem-
ber
1899
(Vol.
1,
Doc.
54),
and Einstein
to
Mar-
cel Grossmann, 6
September
1901
(Vol. 1,
Doc.
122).
[41]
Einstein
to
Mileva Maric,
17
December.
1901 (Vol.
1,
Doc.
128).
Earman
et
al.
1982
suggests
that Einstein
may
have
incorporated
elements
of
his earlier work
on
electrodynamics
into Einstein 1905r
(Doc. 23).
[42]
In 1899 he read Wien 1898
(see note 39),
which
briefly
describes
a
number
of
experimen-
tal
attempts
to
detect the motion
of
the earth
through
the ether. The
Michelson-Morley exper-
iment
is
included
among
those
"with
negative
result"
("mit
negativem
Ergebniss").
[43] See Einstein to
Mileva
Maric,
28
Decem-
ber
1901 (Vol.
1,
Doc.
131).
Einstein
later
stated
that Lorentz 1895
is
the
only
work
by
Lo-
rentz that he knew in 1905
(Einstein
to Carl See-
lig, 19
February
1955).
It
is
possible,
however,
that he learned about
subsequent developments
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