DOC.
14
91
R
8x
a
H
T?
~
JJ
or
M
=

^
=
6.17
x
1023
,
i.e.,
one
atom
of
hydrogen weighs 1/N
gram
=
1.62
x
1024
g.
This is
exactly
the value
found
by
Mr.
Planck,
which
shows
satisfactory
agreement
with values
found
for this
quantity
by
other
methods.
[21]
We
therefore arrive
at
the
following
conclusion: the
greater
the
energy
density and
the
wavelength
of
radiation,
the
more
useful the theoretical
principles
we
have been
using prove to be; however,
these
principles
fail
completely
in
the
case
of small
wavelengths
and
small radiation densities.
In the
following,
we
shall consider
"blackbody
radiation" in connection
with
experience
without
basing
it
on
any
model
for the
production
and
propagation
of radiation.
S3.
On
the
entropy of
radiation
The following
consideration
is contained in
a
famous
study
by
Mr. Wien
and
shall
be presented
here
only
for the
sake of
completeness. [22]
Consider radiation that
occupies
a
volume
v. We assume
that the
observable
properties
of this radiation
are
completely
determined
when
the
radiation
density
p(v)
is
given
for all
frequencies.1 Since radiations of
different
frequencies
are
to be viewed
as
separable
from each
other without
expenditure
of
work
and
without
supply
of heat, the
entropy
of
radiation
can
be represented
in the
form
roo
S
=
v
p(p,v)dv
,
0
where
p
is
a
function of the variables
p
and
v.
One can
reduce
ip
to
a
function
of
a
single variable
by
formulating
the assertion that adiabatic
1This
assumption
is arbitrary.
Naturally,
we
will maintain this
simplest
assumption
as
long
as
the
experimental
results
do
not
force
us
to
abandon
it