DOC.
153
NOVEMBER
1915 153
It
is naturally
easy
to set
these
generally
covariant
equations down; however,
it
is
difficult to
recognize
that
they
are
generalizations
of
Poisson’s
equations,
and
not
easy
to
recognize
that
they fulfill
the
conservation
laws.
Now
the
entire
theory
can
be
simplified conspicuously by selecting
the
frame
of reference in such
a
way
that
y/g
=
1.
Then the
equations
take
on
the
form
ia
ß
mß
a
K(Tim

\gimT)
I
had
considered these
equations
with Grossmann
already 3 years ago,
with
the
exception
of
the
second term
on
the
righthand
side,[10]
but
at
that
time
had
come
to
the
conclusion
that
it did not
fulfill
Newton’s
approximation,
which
was
erroneous.[11]
The clue
leading
to this solution
was my
realization
that
not
gla
d9ai
but the related
Christoffel’s
symbols
im/l
are
to be
regarded
as
the natural
expression
of the
gravitational
field
“component.”[12]
Once
one sees
this,
the
above
equation is
the
simplest conceivable,
because
there
is
no
temptation
to reformulate
it for
the
purpose
of
a general
interpretation through
computing
the
symbols.
The
splendid discovery
I
then
made
was
that
not
only
Newton’s
theory
re
sulted in firstorder
approximation,
but
also
Mercury’s perihelion
motion
(43"
per
century)
in secondorder
approximation.
Solar
light
deflection
came
out twice
the
previous
value.[13]
Freundlich has
a
method
of
measuring light
deflection
by Jupiter.[14]
Only
the
intrigues
of
pitiful persons prevent
this
last
important test
of
the
theory from
being
carried
out.[15]
But
this
is not
so
painful
for
me anyway,
because
the
theory
seems
to
me
to
be
adequately secure, especially
also
with
regard
to
the
qualitative
verification of
the
spectralline
shift.[16]
Now I
am
going
to study
both
of
your
articles[17]
and
then
send
them
back to
you.
Cordial
greetings
from
your raving
Einstein.
I
shall send
you
the
Academy papers
all at the
same
time.