DOC. 42 SPECIAL AND GENERAL RELATIVITY 389
The
Experimental Confirmation
of
the
General
Theory
of
Relativity
149
disc
by o,
i.e.
the
work,
considered
negatively,
which
must
be
performed
on
the unit of
mass
against
the
centrifugal
force in
order
to
transport
it from
the
position
of the clock
on
the
rotating
disc
to
the
centre
of the
disc,
then
we
have
q=_
w2y2
2
From this it
follows
that
v
=
v0(1+o/c2).
In
the
first
place,
we
see
from
this
expression
that
two
clocks
of identical construction
will
go
at
different
rates
when situ-
ated
at
different distances
from
the
centre
of the
disc.
This
result
is
also
valid
from
the
standpoint
of
an
observer who
is
rotating
with the
disc.
Now,
as judged
from the
disc,
the
latter
is
in
a
gravitational
field
of
potential
o,
hence the result
we
have obtained
will
hold
quite generally
for
gravitational
fields. Furthermore,
we
can
regard
an
atom
which
is
emitting spectral
lines
as
a
clock,
so
that
the
following
statement
will hold:
An
atom
absorbs
or
emits
light
of
a frequency
which is
dependent
on
the
potential
of
the
gravitational
field
in
which
it
is situated.
The
frequency
of
an
atom
situated
on
the surface of
a
heav-
enly body
will
be somewhat
less
than the
frequency
of
an
atom
of the
same
element which
is
situated
in
free
space
(or