6
NATURE OF
MOLECULAR FORCES
what
disparagingly
about
Laplace's work.[20]
Two
years
later,
he stated
that
atomistic
ex-
planations
of
capillarity depend on so many arbitrary assumptions
that the
topic
is
"not
so
much clarified
as
obscured"
("nicht sowohl
aufgeklärt,
als verdunkelt")
by
such
expla-
nations.[21]
In
spite
of
a
second note
by
Einstein,
and
a
letter from his
father
appealing
for
a
word
of
encouragement,
Ostwald
apparently
did not
respond.[22]
A review
of
Einstein's
paper
comments
on
the
"not
altogether
clear
and
unobjectionable
derivations"
("nicht
durchweg
klaren und einwandfreien
Herleitungen"),
and notes that
Einstein overlooked
a thermodynamical
relation between two
equations
he
derived.[23]
Einstein 1901
(Doc.
1)
is
cited with
more
favorable comments
several times
in
the litera-
ture
on capillarity,[24]
and
one
of
its
thermodynamical
results
was
later called Einstein's
equation.[25]
Einstein
evidently
was
highly gratified
by
the
ability
of
his
theory
of molecular
forces
to
explain
several
apparently
unrelated
phenomena.
A letter
to Marcel
Grossmann
en-
thuses:
"It
is
a glorious feeling
to
recognize
the
unity
of
a complex
of
phenomena,
which
appear
to direct
sense perception as quite
distinct
things."
("Es
ist ein herrliches Gefühl,
die Einheitlichkeit
eines
Komplexes
von Erscheinungen zu
erkennen, die
der
direkten
sinnlichen
Wahrnehmung
als
ganz getrennte
Dinge erscheinen.")[26]
Even
more
ambitious
hopes
for the
theory
are
suggested by
Einstein's
allusions to
gravitation
in
connection
with
it.[27] Although
he
acknowledged
in Einstein
1901
(Doc.
1)
that his results leave the
ques-
tion
of
whether molecular forces
are
related
to
gravitation
completely
open,
he
continued
to
hope.
In the letter to Grossmann
just
quoted,
Einstein asserted that
a
generalization
of
his
theory
to
gases
would
enable him to
evaluate
c
for
almost all the elements, which
would
take him
a large
step
closer to
settling
this
question.
The next
day
he
wrote to
Maric
expressing
similar
hopes.[28]
However,
there
is
no
further mention
of
the
question
in
his
letters,[29]
nor
in
his second
paper
on
molecular
forces,
Einstein
1902a
(Doc. 2).
Toward
the end
of
1901,
Einstein
hoped
to
obtain
a
doctorate with
a
dissertation
based
[20]
After
praising
Laplace's
phenomenologi-
cal
theory
of
capillarity,
Ostwald stated
that
La-
place's
molecular
forces
"have
not
remained
without contradiction and have not led
to
a
knowledge
of
the
nature
of
these
forces"
("sind
nicht ohne
Widerspruch
geblieben
und haben
zu
einer
Erkenntnis der Natur dieser Kräfte nicht
geführt") (Ostwald 1891,
p.
515).
[21]
Ostwald
1893,
p.
28.
[22]
See Einstein
to
Wilhelm
Ostwald, 3
April
1901 (Vol.
1,
Doc.
95),
and Hermann Einstein
to
Wilhelm
Ostwald,
13
April 1901 (Vol.
1,
Doc.
99).
For
Ostwald's
failure to
reply,
see
Einstein to Mileva
Maric, 10
April
1901 (Vol.
1,
Doc.
97).
[23]
See
Wiedeburg
1901;
see
also Einstein
1901
(Doc.
1),
note 24.
[24]
See
Pockels
1908,
pp.
1123;
Freundlich
1909,
pp.
41, 43-45;
Weber,
R.
H.
1916,
p.
110;
and
Schottky 1929,
p.
116. Kleeman
1909
tries to
develop
Einstein's
theory by assuming,
contrary
to
an argument
in
Einstein's
paper,
that
the surface
energy
is
temperature dependent.
[25]
See
Defay
and
Prigogine 1951,
pp.
38-
40;
and
Einstein
1901
(Doc.
1),
note
3.
[26]
Einstein
to
Marcel
Grossmann, 14 April
1901 (Vol.
1,
Doc.
100).
[27]
Speculations on a
common origin
of
grav-
itation and molecular forces
were
not
uncom-
mon
at the time.
See, e.g.,
Ostwald
1891,
which
attributes the idea
of
a
relation
between the
two
forces to
Van
't Hoff
(see
ibid.,
p. 1142).
[28]
Einstein to Mileva Maric,
15
April
1901
(Vol.
1,
Doc.
101).
[29] However,
Michele Besso refers to the
question
in
a
letter to Einstein
of
7-11
February
1903.
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