30
DOC.
18
JULY
1914
18.
To Max
Planck
Dahlem, 7 July 1914
Dear
Colleague,
On
the
way
home
a
little
maggot popped up,
about
which
I must inform
you
concerning our
discussion.
Take the
case
that the institute
was
established[1] and
my
salary is
reduced
accordingly
by
the
Academy.[2]is
It
then
revealed
sooner or
later that
I
am
not
the
right
man
for
the
direction of
the institute
and for
the
related
work
arising
from
the
endowment to be created
out
of
it,
so
that
I feel
obliged
to
resign my post.
Then
my
livelihood would be
jeopardized
if it
is not
determined
in advance
that the
reduction in
my salary by
the
Academy
should
remain
effective only as long as
I
hold
the
office
concerned.
I
ask
you please
to
bring your
influence
to
bear,
to have this
point taken into consideration.[3]
Then
also
a
brief
reply
to
a
comment
you
made
recently
at
the
Academy
in
the
welcoming
speech.[4]
There is
an
essential difference between
the
reference
system
restriction
introduced
by
classical mechanics
or
the
theory of
relativity
and
that
which
I
apply
in
the
theory
of
gravitation.
For
the latter
can
always
be
adopted
no
matter
how
the
guv's
may
be
selected.[5] To
the
contrary,
the
specialization
introduced
by
the
principle
of
the
constancy
of
the
velocity
of
light presupposes
differential correlations between
the
guv's,
that
is,
correlations
that
ought
to be
very
difficult to
interpret
physically.
Satisfaction
of
these correlations
cannot
be
forced
by
the
appropriate
choice of
a
reference
system
for
any
given
manifold.
According
to
the latter
interpretation,
there
are
two
heterogenic
conditions for
the
guv’s:
1)
the
analogy
of
Poisson’s
equation
2)
the
conditions
that
allow
the introduction
of
a
system
with
constant
c.
With
cordial
greetings, yours,
A. Einstein.
Recipient’s
note: “seen
8
July
1914
Planck."