708 DOCUMENT 496 MARCH 1918
[13]Herglotz
1916.
[14]tiK is Einstein’s
gravitational energy-momentum pseudo-tensor.
[15]See
Kottler
1918,
p.
431,
fn.
1.
[16]Kottler’s
assumption
is
correct.
See Lorentz 1916d and Levi-Civita
1917b;
see
Doc.
368,
note
6,
for
further discussion.
[17]As
was
shown,
e.g.,
in
Schrödinger
1918a
(see
Doc.
393, note 5,
for further
discussion).
[18]In
Einstein 1918a
(Vol.
7,
Doc.
1), p.
167,
it
is
pointed
out that it would be
compatible
with
a
law
of
energy-momentum
conservation
of
the form
GiK
+ kTik
=
0 that
a
material
system
would
simply cease
to
exist
(see
Doc. 368
for
a
similar
argument).
[19]See
Kottler 1916b.
[20]In
Einstein
1916p (Vol. 6,
Doc.
40),
Einstein’s
reply
to
Kottler
1916b,
Kottler’s
statement
that
gravitation
has
a
kinematical
character
is
interpreted as meaning
that
any gravitational
field
can
be
transformed
away
by
a
suitable coordinate transformation. In Kottler
1918,
p.
407,
fn.
1,
the
author
denies that this is what he meant.
[21]The
argument
in this and in the
following paragraphs
is
developed
in
more
detail in
secs.
23-
26
of
Kottler
1918,
in which the exterior and interior fields
of
an
isolated
homogeneous sphere are
calculated.
[22]In sec.
25
of
his
paper,
Kottler makes the
assumption
that the
energy density
of
an
isolated ho-
mogeneous sphere
vanishes and shows that it leads
to
an
interior line element
for
which the relation
g11g44
=
c2
holds.
(This
is the
generalization
for
polar
coordinates
of
the condition
g
=
-c2.)
The
fact that this relation is
satisfied,
Kottler
argues,
makes his solution
preferable
to
other
ones (such as
Schwarzschild’s).
[23]According
to Kottler,
his
assumption
of
vanishing energy density
is
a
"known
postulate" ("be-
kanntes
Postulat,"
Kottler
1918,
p.
439)
of
relativity theory,
because
an
isolated
sphere experiences
no
forces,
so
that its inertia and thus its
mass
vanish.
[24]Stability
of
the
ether
is discussed in
sec.
26
of
the
paper.
[25]In sec.
31
of
the
paper,
Kottler
gives a lengthy quotation
from
Poincaré
1902,
in which Henri
Poincaré discusses
a
situation in which stars
are
invisible and Earth’s inhabitants
assume
that the
Earth is at
rest.
Poincaré
proceeds
to
describe the difficulties that the
description
of
the
dynamical
ef-
fects
of
rotation would
cause-for
instance,
asymmetry
of
space
between left and right-and
predicts
that this will
eventually
lead
to
the conclusion that the earth
rotates.
See also Einstein’s
response
in
Doc. 493
to
a
similar
argument by
Gustav Mie.
[26]Kottler
and Einstein had
met at
the 85th annual
meeting
of
the Gesellschaft Deutscher Natur-
forscher
und Ärzte in
September
1913.
[27]Presumably
the
apparatus
for
producing
and
using
artificial seismic
waves,
developed by
the
geophysicist Ludger Mintrop
(1880-1956).
496. From Romeo Wankmuller
Berlin,
den 30. III. 1918.
Herrn Prof. Einstein
Berlin,
Haberlandstrasse
5.
Sehr verehrter
Herr
Professor!
Einliegend
überreiche ich Ihnen ein
Programm
der ordentlichen
Mitglieder-Ver-
sammlung
der
wissenschaftlichen
Gesellschaft,
für
Luftfahrt,
in
Hamburg, vom
16.-18.
April cr. zur gefl.
Kenntnisnahme.[1]
Herr
Maschke[2]
und ich haben die Absicht den
Vorträgen
dort
beizuwohnen,
und erlaube ich
mir
die
Anfrage,
ob Ihr
Gesundheitszustand
es
erlaubt,
dass Sie
ebenfalls den
Vorträgen
beiwohnen. Selbstverständlich würde meine Firma die
Ko—