DOCS.
185,
186
NOVEMBER
1909
139
herewith
to
stay
with
me
during
Christmas vacation
so
that
we can
work
together.[2]
Cordial
greetings
from
your
A.
Einstein
My
wife also
sends her best
regards
Address Moussonstr.
12
Perhaps
you
could
come on a Sunday
before that.
186.
To
Jean Perrin
Zurich,
11
November
1909
Highly
esteemed
Colleague:[1]
You
can
imagine
with
what
great
interest
I
have
studied
your
article.[2] I
would have
thought
it
impossible
to
investigate
Brownian motion
with such
precision;
it
is
fortunate
for this
material that
you
have
taken
it
up.
I
would not have
thought
that
a measure-
ment
of the
rotations
could
really
be
carried
out.
I
saw
it
as
merely
a
nice
pastime.[3]
A
precise
determination of molecular
sizes[4]
seems
to
me
of
enormous
importance
for the
reason
that Planck's radiation formula
can
be
more
rigorously
tested
by
means
of
such
a
determination than
by
radiation
measurements.
For Planck's
theory
of
radiation
also leads
to
a
determination
of the
absolute
size of the
atom,
one
that
claims
exact
validity.
Hence the
difference
61.1022
(Planck)[5]
& 70.6.1022
(Perrin)[6]
between Planck's
value and
your
value
arouses
concern,
all the
more so
because
it must
be said
that Planck's formula
is
only
apparently
based
on theory.
From
the articles I
am
mailing
to
you
simultaneously
with this
letter,
you
can see
why
the
question
as
to
whether
Planck's
formula
is correct
seems so
important
to
me.[7]
Finally,
I
wish
to
thank
you
from the
bottom of
my
heart
for the
kindness
you
have
shown
me
personally
and
to
ask
you
to
keep
sending me your
admirable
papers,
even
if
they
do
not
deal
with
the
area
of
my
activity.
You
could
just
include
these
reprints
with
those
you
send
to
Prof.
Weiss.[8]
Best
regards
from
your
faithful
A.
Einstein
P.S.
The
errors
in
Svedberg's
method of observation
and also in his
theoretical
treatment[9]
became
immediately
clear
to
me.[10]
At
the
time,
I wrote
a
small
correction
that corrected
only
the
worst
errors
because
I
could not
bring myself
to
spoil
Mr. S's
great pleasure
in his
work.-