76
GENERAL MOLECULAR
THEORY OF
HEAT
of physical
system
for
which
we can
surmise
from
experience
that it
possesses
energy
fluctuation: this is
empty
space
filled with
temperature
radiation.
That
is,
if the linear dimensions
of
a space
filled with
temperature
radiation
are
very
large
in
comparison
with the
wavelength corresponding
to
the
maximum
energy
of
the radiation
at
the
temperature
in question, then the
mean
energy
fluctuation
will
obviously be
very
small in
comparison
with the
mean
radiation
energy
of
that
space.
In
contrast,
if the radiation
space
is
of
the
same
order
of
magnitude
as
that
wavelength,
then the
energy
fluctuation
will
be of
the
same
order
of
magnitude
as
the
energy
of
the radiation
of
the
radiation
space.
Of course,
one can
object
that
we
are
not
permitted
to assert
that
a
radiation
space
should
be
viewed
as a system
of the kind
we
have assumed,
not
even
if
the applicability of the
general
molecular
theory
is
conceded.
Perhaps
one
would have to
assume,
for
example,
that the
boundaries of the
space vary
with its
electromagnetic
states.
However,
these circumstances
need
not be considered,
as we
are
dealing
with orders
of
magnitude
only.
If, then,
in the
equation
obtained in the last section,
we
set
[26] ^
=
Jl
and
according to
the
Stefan-Boltzmann
law
[27]
E
=
cvT4
where
v
denotes the
volume
in
cm3
and
c
the
constant
of
this
law,
then
we
must
obtain for
3v a
value
of the order of
magnitude
of
the
wavelength
of the
maximal
radiation
energy
that
corresponds to
the
temperature
in
question.
One
obtains
=
Lji
=
0^2
?
where
we
have used
for
K
the value obtained
from
the kinetic
theory
of
[28]
gases,
and
7.06
x
10-15
for
c.