318 DOC. 42 SPECIAL AND GENERAL RELATIVITY
TWENTY
The
Equality
of
Inertial
and
Gravitational
Mass
as an Argument
for
the
General Postulate
of
Relativity
[35]
We
imagine
a
large
portion
of
empty space,
so
far
removed
from
stars
and other
appreciable
masses,
that
we
have before
us
approximately
the condi-
tions
required by
the fundamental
law
of Galilei. It
is
then
possible to
choose
a
Galileian
reference-body
for
this
part
of
space
(world),
relative
to
which
points at rest
remain
at rest
and
points
in
motion continue
permanently
in uniform recti-
linear motion.
As reference-body
let
us
imagine
a
spacious
chest
resembling
a room
with
an
observer inside who
is
equipped
with
apparatus.
Gravitation
naturally
does
not
exist
for
this observer. He
must
fasten himself with
strings
to
the
floor,
otherwise the
slightest impact against
the
floor will
cause
him
to
rise
slowly
towards
the
ceiling
of the
room.
To
the middle of the
lid
of the chest
is
fixed
externally
a
hook with
rope
attached,
and
now
a
"being" (what
kind of
a
being
is
immaterial
to
us)
begins pulling
at
this with
a
constant
force.
The
chest
together
with the observer then
begins to
move
"upwards"
with
a
uniformly
accelerated motion. In
course
of time their
velocity
will
reach
unheard-of
values-
75