352
DOCS.
361,
362
JULY
1917
M and
a are
the
mass
and radius
of
the
sphere,
the initial
point
has
the
coordinates:
r
=
b,
p
=
0,
d
=
d.
b
a.
Potentials
higher
than
a2/b2
and
w2
are negligible.
For
very remotely lying points
the
influence
of
the
rotation consists
only
in
an
increase in
the
apparent
mass;
in
the
case
of
initial
points
where
a2/b2
cannot be
disregarded anymore,
a
term
is added,
which breaks
the
field’s
central
symmetry.
Do
you
consider it
possible
that
an
influence
on
Jupiter’s
innermost
moon were
observable? Of all
the
planets,
Jupiter
has
the
largest
w
and the
largest
aI
fear,
though,
that
even
so,
the
effect is
too small
against
the disturbances
of
the
moons amongst
one
another
and
against
the
perihelion
motion.
To
close, a
little
comment
on
your cosmological
paper.[16]
The
“average”
line
element of
the
spherical
world
(eq.
(12),
p. 150) can
be
expressed
very nicely
in
polar
coordinates
which
are
orthogonal
coordinates for
this
space.
It then
reads:[17]
ds2
r2
\
R2r2)
dr2

r2dd2

r2sin2dd(p2
+ dt2.
362. To
Paul
Ehrenfest
Arosa.
[22
July
1917]
Dear
Ehrenfest,
Mr.
Grommer,
a
marvelous mathematician,
whom
you
know from
Göttingen[1]
(to
aid
your
memory,
I
remind
you
of the
enormous
proportions
of his head
and
hands),
would
very
much
like
to
obtain
a
mathematician’s
position
in
Russia,
if
only
a
modest
one.
The
man
is
a
Jew and
a
true
Russian. The
dissertation
he wrote
on
whole
transcendental
functions[2] is
acknowledged
as
superb,
and
he has
a
command of
the
gen.
theory
of
rel. I
have
authorized
him
to offer
a
supplementary
session
to
my
lecture
course on
rel.
th.
in
my
absence.[3]
It
would
be nice if
you
would
recommend the
man
to
your
Russian friends.[4]
I
am
spending happy days
with
my boys
here in Switzerland and
am on
the
way
to
a
proper recovery
again.[5]
Wishing you pleasant holidays, yours,
A.
Einstein
Affectionate
greetings
also
to
your family
&
to Lorentz.