214
THEORY OF
SPECIFIC
HEAT
Doc. 38
PLANCK'S
THEORY OF
RADIATION
AND
THE THEORY
OF
SPECIFIC
HEAT
by
A.
Einstein
[Annalen
der
Physik 22( 1907): 180-190]
In
two
previous
papers1
I
have shown
that the interpretation
of
the
law
of
energy
distribution of
black-body
radiation
in
terms of
Boltzmann's
theory
of
the
second
law
leads
to
a
new
conception of
the
phenomena
of
light emission
and
light absorption,
which,
even though
still far
from
having
the character
of
a complete
theory,
is remarkable insofar
as
it
facilitates the understand-
ing
of
a
series
of
regularities.
The
present
paper
will
show
that the
theory
of
radiation-in
particular
Planck's
theory-leads
to
a
modification
of
the
molecular-kinetic
theory
of heat
by
which
some
difficulties
obstructing
the
implementation
of that
theory
can
be
eliminated.
The
paper
will also
yield
a
[2]
relationship
between
the thermal
and optical
behavior of solids.
First
we
will
give
a
derivation of the
mean
energy
of Planck's
resonator
that
clearly
demonstrates
its relation
to
molecular
mechanics.
To
that
end
we use a
few
results of the
general
molecular
theory
of
[3]
heat.1
Let
the
state
of
a
system
in the
sense
of the molecular
theory
be
completely
determined
by
the
(very
many)
variables
P1,P2...Pn.
Let
the
molecular
process
proceed according
to
the
equations
dPv/dt
=
Qv(P1,P2...Pn),
(v
=
1,2...n)
,
and
let the
relation
[4]
(1)D
0
V
hold for all values
of
the
Pv's.
[1]
1A.
Einstein,
Ann. d.
Phys. 17
(1905): 132 and 20
(1905):
199.
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