DOCS.
90,
91
JUNE
1915 107
Thus
there
would be
accordingly 2 types
of
polar symmetric charge
at
equilibrium:
(1)
Charge
of
density
one (negative
elementary
charge)
(2)
Charge
with variable
densities,
therefore
larger
mass
and
rings
of
vanishing
force in which
areas
of
embedded
charges
at
equilibrium may exist.)
Before
I
continue
working
on
this,
I
would
like
to hear
your opinion, esp.
on
the
following points
(a)
Would
the
as
yet
not
used
eq.
(42c)
deliver
another
new
condition?[6]
(b)
How
do
(81) (42c)
and
(81b)
read with
polar symmetry,
as
tvo,
of
course,
covariant
only against
linear transformations?[7]
(c)
May
it
be
regarded
perhaps
as
a
first-order
approximation
when
you
set
g11 g22 g33
=
const.?
(d)
Surely
for
polar
coordinates
eq.
(54)
must read
differently.
Is
it
permissible
then
also
to
call
(54)
invariant
against
arbitrary
transformations?[8]
You
may
find these
questions very
idiotic,
but
perhaps
these
are precisely
the
hitches
keeping me
from
moving
forward.
With
humblest
regards, yours,
H. Reissner.
91.
To David Hilbert
[Berlin,
24
June
1915]
Dear
Colleague,[1]
Many
thanks
for
both
of
the cheerful
postcards.
I
am
going
to
stay
at
the
Gebhart
Hotel
and shall
call
on you Monday
morning.[2]
With best
regards, yours very truly,
A.
Einstein.