538
DOCS. 517-519 APRIL
1918
in
earnest,
for Mama’s
love
for Mr.
O.
seems
to
belong
so
entirely
to
the
past[3]
that what
remains could
not
even
serve
to blacken
a
fingernail.
We
are
very eager
to have her here with
us.[4]
Now is
also
the best
time for
walks, you
know;
but
in order not to starve
along
the
way, one
must
bring along
one’s
slice
of
bread
[Stulle].[5]
With
warm
regards
and
once
again many
thanks,
yours,
Albert.
[...][6]
[5]Berlin
dialect for
open-faced
sandwiches.
518. From Felix
Klein
Göttingen, 25 April 1918
Esteemed
Colleague,
You
will
be
seeing
Sommerfeld,
of
course,
in
the
next
few
days
on
the
occasion
of
the
Planck
festivities;[1]
I
have
already
written
him
that
he
best
discuss
my
elaboration with
you personally. Besides,
I
would
appreciate
it
if Dr. Freundlich
also
were
willing
to review
my
elaboration.[2]
A
factual remark
(about
which I wrote to
de Sitter
lately
in
more
detail):[3]
In
your “Cosmological
Considerations”
of
1917,
the
spherical space
cannot be
substituted
by
an
elliptic one:[4] Namely,
because
the
“elliptic”
plane
is
a
one-
sided
surface
(or as
I
said earlier:
a
double
surface)
where the direction of rotation
of
an
indicatrix
reverses
again
when sent
over
the
surface,
a
specific
arrow
cannot
be
assigned
to
the
world lines
of
its points-in
other
words,
no
distinction
can
be made between
past
and
future.[5]
Very
truly
yours,
Klein.
519. To
Mileva Einstein-Maric
[Berlin,]
26
April
1918
Dear
Mileva,
I’m
giving
in
about the
children because
I
have
now come
to
the
conviction
that
you
want to handle matters
in
a
conciliatory
manner.
Of
course,
I
would
absolutely
not have
the
children
travel here alone in these times.
Maybe you