444
DOCS.
437,
438
JANUARY
1918
437. To
Pieter Zeeman
Berlin, 16 January 1918
Esteemed
Colleague,
Cordial
thanks
for
your
articles and for
the
commentary
thereon
in
your
letter,[1] as
well
as
for
your
wonderful earlier
papers on
the
ether-drag
coefficient.[2]
Among your
recent
investigations,
those
about the inertial
and
gravitational
mass
of
uranyl
nitrate
interest
me
most.[3]
Regarding
the
investigations
on
the
grav-
itation
and
inertia
of
crystalline substances,
the theoretical
background
to
the
problem
is
unfamiliar
to
me;[4]
even so,
I
understand that the
issues
can
be
addressed
without
such
theoretical
points of
view,
particularly
at
this time
of
revision of
the
general
foundations of
gravitation theory.
Cordial
regards, yours
very truly,
A.
Einstein
(This
letter
was
dictated
from
bed,
because
I
am
ill.)[5]
438.
To
Erwin Freundlich
[Berlin,
before
17
January
1918][1]
Dear
Freundlich,
Perhaps
it
is
better
if I
use
my personal
influence
concerning
that
instrument,
since
no
bellicose odium
weighs on
me.[2]
I
am on
the
Council of
the
Anti
Orlog
Raad,
you
know.[3] I
am
very pleased
that
you
are
being
received
so
amicably
at
Potsdam.[4] The ice
seems
finally
to
have broken.
The
notice
by
de Donder
is
scandalously superficial.
I
am
amazed
that
Lorentz
was
taken
in
by
it,
or
accepted
it
without
closer consideration.[5]
The
error
in
the
chain
of
reasoning
is,
as you yourself
indicated in
your
letter,
that
(16)
does
not
follow
from
(15).
(15)
is
not
an
identity
but
an
equation of
condition.
The
deduction
is
approximately
thus.
Assertion:
No circle
can
exist
on a
plane.
Proof:
The circle
equation
x2
+
y2
=
R2
is
intrinsically inconsistent;
for since
the
right-hand
side
is independent
of
x,
the
left-hand
side
must
also be.
The
equation
is
therefore inadmissible!