262
DOCS.
273,
274
NOVEMBER
1916
is
determined
by
the
masses
present
there
and
only
by
these
masses.
A
specific
inertia-generating
envelope
is not
assumed;
rather,
all
inertia-generating matter
will consist of
stars,
as
those in the
portion of
our
universe accessible
to
our
telescopes.
This
is
compatible
with
the
facts
only
when
we
imagine
that the
portion
of
the
universe visible to
us
must be considered
extremely
small
(with
regard
to
mass)
against
the
universe
as a
whole. This
view
played
an
important
role for
me
psychologically,
since it
gave me
the
courage
to
continue to work at
the
problem
when I
absolutely
could not find
a way
of obtaining
covariant
field
equations.[6]
Now
that the
covariant
field
equations
have been
found,
no
motive remains to
place
such
great
weight
on
the
total
relativity
of
inertia. I
can
then
join
you
in
putting
it
this
way.
I
always
have to describe
a
certain
portion
of
the
universe. In
this
portion
the
guv's (as
well
as
the
inertia)
are
determined
by
the
masses
present
in
the
observed
portion of
space
and
by
the
guv's at
the
boundary.
Which
part
of
the inertia stems from
the
masses
and which
part
from
the
boundary
conditions
depends
on
the
choice
of
the
boundary.
In
practice I
must,
and in
theory
I
can
make do with
this,
and
I
am
not
at
all
unhappy
when
you reject
all
questions
that
delve
further.
On
the other
hand,
you
must
not scold
me
for
being
curious
enough
still
to ask:
Can
I
imagine a
universe
or
the
universe in such
a way
that inertia
stems
entirely
from
the
masses
and not at all from
the
boundary
conditions?
As
long
as
I
am
clearly
aware
that
this
whim
does
not
touch
the
core
of
the
theory,
it
is
innocent; by
no means
do
I
expect
you
to
share
this
curiosity!
Have
a
look
at
the
printer’s proof
I
sent
to
Ehrenfest. The link between
the
relat.
postulate
and
the
energy
conservation
law
emerges
particularly clearly
there.[7]
Cordial
greetings, yours,
Einstein.
274. To Wilhelm Ostwald
[Berlin,
6
November
1916]
Highly
esteemed
Colleague,[1]
I
thank
you cordially
for
the
paper on
color
theory,[2]
which
I
am
reading
with enchantment
for
the
second
time
already.
Science
is
indebted
to
you
for
a
significant
advance here.
I want
to
present
it
to
our
colleagues
in
Rubens’s
seminar;[3]
they
also
will
be
delighted
with it.
With
respectful regards, yours
truly,
A.
Einstein.