DOC.
308
MARCH
1917
297
throughout
because, according
to
experience,
the
energy density
does
not
become
negative.
The
newly
introduced
A
has
nothing to
do with
the
earlier
one.
I
failed
to notice
then
that
on
the
left-hand side of
the
field
equation
an
addition
of
+\guv
does not
disturb the
tensor
character.
I
initially
ought
to have set
A
=
0
in Newton’s
sense.
But
the
new
considerations
plead
for
a
A
differing
from
zero,
which
tends
toward
producing
a non-zero mean
density
p0
of matter.[8]
Fixed-star
astronomy (star
counts)
points
to
the
order
of
magnitude
p0
=
10-22gram/cm3,
corresponding
to
a
world radius of R
=
107
light-years,[9]
while
the farthest
visible
stars
are
estimated
at
104
light-years.
Read the
paper
with
Dällenbach.
It will
amuse you
both.
Dear
Michele,
back
to Earth,
which
is
so
ugly only
because
we are seeing
and
experiencing
it too
keenly.
Unless
my appearance
in
Zurich does
not
suddenly
become
necessary,
I’m not
coming
until
the
summer.
We’ll
all
get more
out of
it,
especially my
Albert.
I
am
looking
forward
to
it
immensely already.
I
ask
Zangger
to set
the
package
aside until
that
time;[10]
then
it
is
sure
to
arrive
safely
at
its destination.
There
is
no question
of
my taking
Albert
away against
Miza’s
will.[11]
I
am no
ruthless
tyrant,
you
know. I
know
that
some
other
things argue
against
it
as
well.
If
the
boy
is
not
endangered physically by
his environment and
is
content,
then he
should
very
well
stay
there. Here he has
just
me,
while
I
would
have to shield him from
other
influences. There he has
a
healthy
environment
with his
same-aged
friends
at
the
Swiss
school and with
you
all. I
would have to
expend a
major part
of
my
energy,
which
is
anyway weakened,
on
him and his
education
and
manage a proper
household,
which
would
be
very complicated
for
me.
I’ll
do it
only
if,
according
to
our
unanimous
opinion,
it
is
the
right thing,
not
out of blind
preference.
If
I
know him to be
well
cared for and
content,
I
also
am
satisfied. It
is
lucky
that
I
got
the
position here,
otherwise
I
would be
completely
ruined
financially.
But this
way
I
have
put
away
handsome
savings. Keep an
eye
out
that
Zangger
does
not have
to
pay
for
anything
in his
solicitude![12]
If
the
money
does not
suffice,
I
shall send
more.
Ask
him,
appealing
to his conscience.
I
do
not
have
the
courage
or
the
skill
to
ask him
properly.
I
have
enough,
since
I
have been
living extremely frugally.
Affectionate
greetings
also
to
Anna and
Vero,
yours,
Albert.