FOUNDATIONS OF
STATISTICAL
PHYSICS 45
Aside from his
reading
of
material
directly
concerned with kinetic
theory,
Einstein
was
studying
at least three other
topics
in 1901
and 1902 that
may
have
suggested
the need to
extend the foundations
of
thermodynamics
and kinetic
theory.[35]
First,
since at least the
spring
of
1901,
Einstein had been
reading
Planck's
papers on
irreversible radiation
processes,
in which Planck
sought
to extend the
concept
of
entropy
to radiation.[36]
Second,
Einstein
was studying
the work
of
Drude and others
on
the electron
theory
of
metals,
in which the
apparatus
of
kinetic
theory
is
employed
to
explain
such
phenomena
as
electrical and thermal
conductivity.[37] Especially important
for
Einstein's
conception
of
the foundations
of
statistical
physics was
his
reading
in
late
May
1901
of
a
paper
by
Reinganum
that convinced him
completely
of
the
validity
of
the electron
theory.[38]
Rein-
ganum
showed that the
principal
results
of Drude's
electron
theory can
be
derived
without
any assumptions
about the nature
of
the
elementary charge
carriers
or
the mechanism
of
their interactions with the atoms
of
a
metal. The
only
crucial
assumption
is
that
the
equi-
partition
theorem
applies
to
a gas
of
moving charge
carriers.
Reinganum
concluded:
It
appears
therefore
.
. .
that
in metals,
too,
electricity moves
in discrete
quantities
with
the
magnitude
of
the
charges on electrolytic
ions,
and that the
principles
of
the
gas
theory
are
applicable
to
the
masses moving
with the
charges.
Es erscheint daher
. . .
dass auch
in
den Metallen die Elektricität in
discreten
Mengen von
der Grösse
elektrolytischer Ionenladungen
sich
bewegt,
und dass
für die mit den
Ladungen bewegten
Massen die
Principien
der Gastheorie
anzuwenden sind.[39]
Reinganum's
results
helped
to
confirm
Einstein's
commitment to
an
atomistic view
of
electricity, as
well
as
of
matter;
but
they may
also have
suggested
that the
equipartition
theorem,
as a
vital
principle
of
statistical
physics,
needed
a more general
mechanical foun-
dation than it had hitherto been
given.
In
fact,
one
of
the
major
results of
Einstein
1902b
(Doc.
3)
is
precisely
a
demonstration that the
equipartition
theorem
is
valid not
only
for
a
[35]
Anticipations
of Einstein's
later distinc-
tion between
"theories
of
principle"
and
"con-
structive
theories"
(see
Einstein
1919) may
also
have inclined him
to
seek
more
general
founda-
tions for
thermodynamics
and the kinetic
theory.
For
a
discussion
of
the
distinction, see
the Intro-
duction,
pp.
xxi-xxii.
[36]
Einstein
apparently
studied
one
or
both
of
Planck
1900a, 1900b;
see
Einstein to Mileva
Maric,
4
April
1901
and
10
April
1901
(Vol. 1,
Docs. 96 and
97).
For
a
discussion
of Einstein's
interest in
Planck's
work,
see
Vol.
1,
the edito-
rial
note,
"Einstein
on
Thermal, Electrical,
and
Radiation Phenomena,"
pp.
235-237.
See also
Einstein
to Maric,
second
half
of
May 1901,
4
June
1901,
and
7
July
1901 (Vol.
1,
Docs.
110,
112,
and
114),
as
well
as
Einstein to Jost Win-
teler, 8 July 1901 (Vol.
1,
Doc.
115).
[37]
His
reading
included at least
Drude
1900a,
1900b
(see
Einstein
to Mileva
Maric,
4
April
1901,
and 28
May 1901,
Vol.
1,
Docs. 96
and
111).
For
a
discussion
of Einstein's
interest
in the electron
theory
of
metals, see
Vol.
1,
the
editorial
note,
"Einstein
on Thermal, Electrical,
and Radiation Phenomena,"
pp.
235-237.
[38]
See
Reinganum
1900. For Einstein's
com-
ments
on
it,
see
Einstein
to
Mileva
Maric,
28
May
1901 (Vol.
1,
Doc.
111).
[39]
Reinganum
1900,
p.
403.
Reinganum's
comments
concern primarily
Drude
1900a.