358
DOCS.
478-480 OCTOBER-NOVEMBER
1913
charming
such
a
life with
very
small
needs and without
grandeur
can
be!
Who
is to
say
that
we
will
not
realize
it
one
of these
days?
Cordial
greetings
to
you
and
the
little
stepchildren,[9]
and
earnest kisses
to
you
alone
from
your
Albert
479. To
Robert Gnehm
Zurich, 19
October
1913
To the President of the
Swiss School Council
Highly
esteemed
Mr. President:
Confirming
earlier
discussions,
the
undersigned
have
the honor
to
inform
you
that
they
have
been
invited
to
participate at
the Conseil
international
de
Physique
Solvay,[1]
which will
take
place
in Brussels from 27
October
to
1
November.
They
wish to
request
that
you kindly
grant
them
a
leave
of absence
extending
through
that
week.[2]
Respectfully,
P.
Weiss
A.
Einstein
480.
To
Ludwig Hopf
Zurich, 2
November
[1913][1]
Dear
Mr.
Hopf,
Thank
you
so
much
for
your
kind
invitation,
which
I
would have
been
delighted
to
accept.
But
I
could
not
even
think of
it,
since I must call
myself happy
if I
can
fulfill
my
paper-writing
obligations even
after
having
renounced
all
pleasure-giving extravagance.
Above
all,
my
warmest congratulations
on
the birth of
your strapping
boy.[2]
May
he be
as
healthy
and
intelligent
as
his old
man,
but
in
addition
also
a
little
more
industrious.
I
am now very
satisfied with the
gravitation
theory.
The
fact
that
the
gravitational
equations
are
not generally covariant,
which still
bothered
me so
much
some
time
ago,[3]
has
proved to
be
unavoidable; it
can
easily
be
proved
that
a
theory
with
generally
covariant
equations cannot
exist if it
is
required
that
the field
be
mathematically
completely
determined
by
the
matter.[4]
In Brussels
the
lecture of
Bragg
Sr.
was
extremely interesting.[5]
It
is
unbelievable
how much this
man
has
already
found
out
about
the lattice structure
of
crystals
and
about
Röntgen
rays. Now,
all
at
once,
it
is
possible
to
carry
out
exact
determinations
of