218 DOCUMENT 187 NOVEMBER 1909
[3]Perrin 1909 includes
experimental
results
on
rotatory
Brownian
motion,
which had been
theoretically
treated in Einstein 1906b
(Vol. 2,
Doc.
32), pp.
379-380.
[4]Here
the
expression
"Grösse der Moleküle,"
as
well
as
"Grösse des Atoms," which
is
used
below,
refers
to Avogadro's
number. See Einstein 1904
(Vol. 2,
Doc.
5),
pp. 358-359,
and
Einstein
1979, pp. 38,
44,
for other instances of this
usage.
[5]Planck 1906c,
p. 162,
gives 61.75x1022 (calculated
from
experimental
data and
using
his
radiation
law).
[6]The
value for
Avogadro's
number characterized
by
Perrin
as
"the
most probable" ("la
plus probable") is in
fact
70.5x1022 (Perrin
1909,
p. 111).
[7]Probably
Einstein's
most recent papers
on
radiation
theory,
Einstein
1909b
(Vol. 2,
Doc.
56)
and Einstein 1909c
(Vol. 2,
Doc.
60).
[8]Pierre Weiss.
[9]The
Svedberg
(1884-1971)
was
docent
in
chemistry
at
the
University
of
Uppsala.
His
theoretical
(and
experimental)
work
on
Brownian motion referred
to
by
Einstein
is in
Svedberg
1906a,
1906b.
See
Perrin
1909, pp.
72-74, for Perrin's criticism.
[10]Einstein
1907c
(Vol. 2,
Doc.40).
See
also
Vol. 2,
the editorial note, "Einstein
on Brown-
ian Motion,"
pp.
219-220, for
a
discussion of Svedberg's work
and
Einstein's criticism.
[11]On p.
26
of Perrin 1909 it
is
suggested
that the osmotic
pressure
on a
semipermeable
barrier
separating
a
solution from
a
quantity
of
pure
solvent
is
caused
by
the collisions of the
solute molecules
against
the barrier.
[12]This
was
done
in
Einstein's
dissertation,
Einstein
1905j (Vol. 2,
Doc.
15).
See Vol.
2,
the
editorial
note,
"Einstein's Dissertation
on
the Determination of Molecular
Dimensions,"
pp.
170-182,
for
more
details.
[13]In
1910
Jacques
Bancelin
performed experiments
in
Perrin's
laboratory,
in
which the
viscosity
coefficient of
a
suspension
was
correlated with the total volume
occupied
by
the
sus-
pended particles.
He found
a
discrepancy
with Einstein's theoretical
prediction
(Bancelin
1911a,
1911b).
See
Docs.
239, 241, and
244 for
more
details
and Vol.
2,
the editorial
note,
"Einstein's Dissertation
on
the Determination of Molecular
Dimensions,"
pp.
179-182,
for
a
discussion.
[14]Paul
Langevin
(1872-1946)
was
Professor of
Experimental
Physics at
the
College
de
France.
187.
To
Michele Besso
[Zurich,
17
November
1909]
Lieber Michele!
Ich danke Dir bestens für Deine Karte. Den Aufsatz in der Umschau hatte
ich
schon
gelesen.[1]
Es scheint,
dass der inverse Prozess
zum
photochemi-
schen
von
selbst
vor
sich
geht,
insbesondere bei den
Vorgängen,
welche
schwacher
Belichtung entsprechen.
Eine Art
dynamisches Gleichgewicht
daraus,
also nicht Vorschreiten der Reaktion mit wachsender Zeit. Reiz-
schwelle warscheinlich scheinbar. Photochemische Prozesse scheinen des-
halb
ungeeignet
zur
Prüfung
der
Quantenhypothese.[2]
Ich bin sehr
beschäftigt
mit den
Vorlesungen,
sodass meine wirkliche freie
Zeit
weniger
ist
als in Bern.[3]
Aber
man
lernt viel dabe.
In
Lichtquanten
we-
nig
und ohne
Erfolg gegrübelt.
Habe Stodola einmal
gesprochen.[4]
Er ist
ein
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