340
DOC. 448
JUNE
1913
448. To
Ernst Mach
Zurich, 25
June
1913
Highly
esteemed
Colleague,
You
have
probably
received
a
few
days ago my
new
paper
on
relativity
and
gravitation,[1]
which
is
now finally completed
after
unceasing
toil and
tormenting
doubts.
Next
year,
during
the solar
eclipse,[2] we
shall
learn whether
light rays
are
deflected
by
the
sun,
or
in other
words,
whether
the
underlying
fundamental
assumption
of the
equivalence
of the acceleration of the reference
system, on
the
one
hand,
and the
gravitational field,
on
the other
hand, is
really
correct.
If
yes,
then-in
spite
of Planck's
unjustified
criticism-your
brilliant
investigations
on
the foundations of
mechanics will have received
a
splendid
confirmation.[3]
For
it
follows
of
necessity
that
inertia has its
origin
in
some
kind
of
interaction
of the
bodies,
exactly
in
accordance
with
your argument
about Newton's bucket
experiment.[4]
You will find
a
first
consequence
in this
sense on
the
top
of
page
6
of the
paper. [5]
Beyond
that,
the
following
results
have
been
obtained:[6]
1.
If
one
accelerates
an
inertial
spherical
shell
S,
then,
according
to
the
theory,
a body
enclosed
by
it
experiences
an
accelerating
force.
2.
If
the
shell
S rotates
about
an
axis
passing
through
its
center
(relative
to
the
fixed stars
("Restsystem"),
then
a
Coriolis field
arises
inside the
shell, i.e.,
the
plane
of
the
Foucault
pendulum
is
being
carried
along
(though
with
a
practically
immeasurably
small
velocity).
It
gives
me
great
pleasure
to
be
able
tell
you
about
this,
all
the
more
so
because
Planck's
criticism
always
seemed
to
me
to
be most
unjustified.
With
kindest
regards,
I remain
very respectfully yours,
A.
Einstein
Thank
you sincerely
for
sending
me
your
book.