DOCS. 169-170 DECEMBER
1915 165
Mercury’s perihelion
and
approximately solved.
It
is
easy
to
specify
the
most
general
line element which has
the
necessary
symmetry properties. Proceeding
from
this,
I
initially
determined the first-order
approximation
in
your way
and
found:
9pa =
-axpxo/r3 -
ßxpxo/r3
= Spa
[B/3r3]
g44 =
1,
therefore,
two arbitrary
quantities
a
and
ß,
which
was
peculiar.
Then
I moved to
the
solution
as a
whole.”
170. To Hans Albert Einstein
Berlin,
23
December
1915
My
dear
Albert,
I
have been
working
so
hard
in
the last
few
months
that
I
urgently
need
a
rest
during
the Christmas
holidays.
Aside from
this, coming
across
the border
is
very
uncertain
at
present,
since it has been almost
constantly
closed
recently.[1]
That
is
why
I
must
unfortunately
deprive myself
of
visiting you
now.
But
instead
I’m
definitely coming
in
the
first
days
of
April.
Then
I
have
more
time and
can
wait
at
the border until
I
am
allowed
into
Switzerland. I
have
sent
my
Christmas
gift
to
you
both
in
the
form
of
money,
according
to
your
wish. I’m
glad
that
you
romp
around
a
lot
out
of
doors. I
hope
there
will
continue
to
be
a
decent
amount
of
snow as
well
so
that
you
can
do
your skiing.
Ask Mama to send
me a
photo of
you
both
again.
You
have
grown
again
and have
changed
since
the last
one.
Write
me
about the
things you
are
up
to besides
school,
and who
your
friends
are.
Is
there
a
subject
in
or
outside
of
school
that
interests
you
particularly?
Then
I
would also
like
to hear from
you
what
schooling you
have ahead of
you,
because
I
am
not
exactly
familiar with the Zurich school
system.[2]
How is
Tete’s
health?
Does he
ever
have
complaints?
Does
he
look
well?
Now
to
something
else
of
importance.
I
have heard
that there
is
an
excellent
remedy
for
tooth and
bone
development especially
for
growing
children,
which
you
both
should take.
You
prepare
a
saturated
solution
of
calcium chloride
(CaCl2)
and
store
it in
a
corked medicine
bottle.
After
every
meal
you
put
one
little
teaspoonful
of it in half
a
glass
of water
(or milk)
and drink it.
It
would be
a
true
blessing
for Tete
if
he
were
to take it. You
see,
calcium
(Ca)
is
a
metal
that
plays
a
major
role in
teeth
and bones.
It
is
present
in
a digestible
form in
natural
food,
but
during
cooking
it
precipitates
out in
an
indigestible
form
so
the
body
cannot
benefit from it
any
more.
Talk also to Mama
about
this;
she
will
immediately
see
the
sense
in it.
Write to
me
again soon, my
dear
Albert,
and
on
replying
have
my
letter
before
you
and
answer
everything
I
have asked
you.
In this
way
it’s also easier for
you