DOC.
360
FEBRUARY
1912 263
These
two
numbers
must
be
equal.
Thus,
pCA/CBCC
is
determined
only
by
the
temperature
of
the
gas.
But,
without
changing
the
temperature
of the
gas,
there
also
exist,
as
follows from this
argument,
other
thermodynamic equilibria
in which
the
temperature
of radiation
deviates from
the
value
pCA
p
which
corresponds
to
the
temperature
of the
gas.
Let
us
set
=
K
for the
CBCC
"normal" thermod.
equilibrium.
One
can
then obtain
a
new equilibrium
at
the
same gas
temperature,
if
one
alters,
say,
p
and
CA
in such
a
way
that
the
product
pCA
remains
unchanged.
For
if
one
leaves
CB
and
Cc
unchanged,
then
K
remains
unchanged, i.e.,
the
number of
decomposing
molecules
A is
always
equal to
the
number of
the
newly forming
molecules.
If
one now
formulates the condition
for
the
entropy
of
a
system
in
any
of these
equilibrium
states to be
an
extremum,
one
obtains
simultaneously
the
Wien
radiation
law
and
the abovementioned hv
law.
The
fact
that
one
obtains Wien's and
not
Planck's
law
shows
that both the hv
law and
the indicated
basic
assumptions
hold
only
for weak
radiation.
The
second
thing concerns
the
relationship
of
gravitational
fieldacceleration
fieldvelocity
of
light.[6]
Simple
and
beautiful
things
emerge
from here
quite
automatically.
The
velocity
of
light c
is
variable.
It determines
the
gravitational
force.
dc dc dc
A
stationary point
with
mass 1
is
acted
upon
by
the
force


 .
In the
dx
dy
dz
empty space c
satisfies
Laplace's equation.
The inertial
mass
of
a
body
is
m,
that
is,
it
c
decreases
with
the
gravitational potential.
The
equations
of motion for the material
point agree
essentially
with
those of
the
customary theory
of
relativity.
Abraham's
theory
is
incorrect
in
every
respect
if
there
really
is
an equivalence
between the
gravitational
field and
the
"acceleration field."[7]
I
remember
your
having
told
me
that
you
often
come
to Switzerland in the
summer.
I
would be
immensely happy
if
I
could
see
you again
on
such
an
occasion.
Beginning
in
August,
I will be in
Zurich
again.
It would be
an
incomparable pleasure
to
be able to
have
you
and
Mrs.
Lorentz[8]
as guests
in
my
house.
Please
give my
best
regards to
colleagues
Kamerlingh
Onnes and
Künen,[9]
and
convey
to
them
my
thanks
for
their
great
trust in
me.
With
cordial
greetings
to
you,
Mrs.
Lorentz
and
your
children,
also from
my
wife, I
remain
yours very respectfully,
A.
Einstein