BROWNIAN MOTION 211
nehmbare
ungeordnete Bewegung
ausführen müssen, welche durch die Wär-
mebewegung
erzeugt ist.[35]
Einstein wrote this
paper
"without
knowing
that observations
concerning
Brownian
motion
were already long
familiar"
("ohne
zu
wissen,
dass
Beobachtungen
über die
'Brown'sche
Bewegung'
schon
lange
bekannt
waren").[36]
He did not mention Brownian
motion
in the
title
of
Einstein 1905k
(Doc. 16),
although
in the text he
conjectured
that
the
motion he
predicted
might
be identical to Brownian
motion.[37]
Boltzmann's
Gastheorie,
which Einstein
carefully
studied
during
his student
years, explicitly
denies
that
the thermal
motion
of
molecules
in
a
gas
leads to observable motions
of
suspended
bodies.[38] (This
denial
may
be
an
instance
of
what
Einstein referred
to
as
Boltzmann's
attaching
too little
importance
to
a
comparison
of
theory
with
observation.[39])
Some time between
1902 and
1905,
Einstein read
Poincare's
Science
et hypothese,
which
contains
a
brief
discussion
of
Gouy's
work
on
Brownian
motion,
emphasizing
Gouy's
argument
that Brownian motion
violates the second law
of
thermodynamics.[40]
Einstein's
second
paper
on
Brownian
mo-
tion,
written after
Siedentopf
drew his
attention to
Gouy's
work,[41]
cites the
observations
reported
in
Gouy
1888
as qualitative
confirmation
of
his results.
Einstein
1905k
(Doc.
16)
opens
with the derivation
of
an expression
for the coefficient
of
diffusion
in
terms
of
the radius
of
the
suspended particles,
and the
temperature
and
viscosity
of
the
liquid, an expression already
obtained in
Einstein's
doctoral disserta-
tion.[42]
Unlike the
previous
derivation,
however,
the
new one
makes
use
of
the methods
of
statistical
physics
that Einstein
developed.
The
new
approach
is
different
in two
respects:
(1)
In his dissertation, which deals with solutions rather than
suspensions,
Einstein
simply
assumed the
validity
of
Van
't Hoff's
law for the osmotic
pres-
sure.
He
now gave a
derivation
of
this
law from
an expression
for the free
energy
of
the
suspension
that follows from statistical mechanics.
(2)
Rather than
simply considering
the
equilibrium
of
forces
acting on a single
molecule,
Einstein derived the
equilibrium
between the osmotic
pressure
and
a
friction force
obeying
Stokes's law
by
a
thermodynamical argument.[43]
[35]
Einstein to Conrad
Habicht, 18
May-8
June
1905.
[36]
Einstein
1979,
p.
44; translation,
p.
45.
See also Einstein
to
Michele
Besso,
6
January
1948,
and Einstein to Carl
Seelig,
15
September
1952.
[37]
In Einstein
to
Conrad
Habicht, 18 May-8
June
1905,
he wrote:
"Unexplained move-
ments
of
inanimate small
suspended
bodies have
in
fact
been observed
by
physiologists, move-
ments which
they
call
'Brownian
molecular
mo-
tion'
" ("[E]s
sind
unerklärte
Bewegungen
lebloser kleiner
suspendirter
Körper
in der That
beobachtet
worden
von
den
Physiologen,
welche
Bewegungen
von
ihnen
'Brown-sche
Molekularbewegung'
genannt
wird").
[38]
See Boltzmann
1898a,
pp.
111-112.
For
evidence
that Einstein read the Gastheorie,
see
note 12.
[39]
See
note 15
above.
[40]
See
Poincare
1902,
p.
209. For
Einstein's
reading
of
Poincare,
see
the Introduction,
p.
xxv.
[41]
See
Einstein
1906b
(Doc. 32), p.
371.
[42]
See
Einstein
1905j (Doc. 15), p.
19.
[43]
A sketch
of
this
derivation is found
in
Ein-
stein
1905j (Doc. 15),
§
4. Some
of Einstein's
contemporaries
considered the
application
of
Previous Page Next Page