DOCS.
238,
239
DECEMBER
1910 169
238.
From Count Karl
von
Stürgkh
Vienna,
15
December
1910
Highly
honored
Sir:
With
reference
to
the
statement
you gave
here
in
writing some
time
ago,[1]
I have
the
honor
to
inform
you
that
you
have
been
appointed Ordinary
Professor of Theoretical
Physics
at
the German
University
of
Prague,
with the
salary
stipulated
in
the
existing
regulations,[2]
effective
1
April
1911.[3]
Most
respectfully,
239. To
Ludwig Hopf
[Zurich] Tuesday
[27
December
1910][1]
Dear
Mr.
Hopf,
I
thank
you
once
again
for
the
splendid
toys you
sent
for
my
son,
and
I
thank
your
parents[2]
for
sending
the
sweets.
The
airship
presents
us physicists
with
a
hard
little
nut
to crack,
because
it
always
circles in
the
same
direction. Whoever
comes
to
visit
me
has
this little marvel shown
to him.
The
news
in
physics
is
as
follows.
Perrin
has had
a young physicist
do
an experimen-
tal
investigation
of
the
viscosity
of
mastic
emulsions.[3]
He
found[4]
7?
= 7]0(1
+
3.8cp)
t]q
=
viscosity
of
the
solvent
r}
= "
of the
suspension
cp
=
volume
of
the
substance
suspended
(in
spherical form) per
unit volume of
the
latter.
The
investigation
was
performed
in
order
to test
a
formula that
I
derived.[5]
But
my
formula reads
V = Vo(1
+
P)
The
thing
is
important
because
from the
viscosity one
can
learn
something
about
the
volume
of the
dissolved molecules.
I
rechecked
my
old calculations
& arguments
and could find
no errors
in
them. You
would do
a
great
service
to
the
cause
if
you
made
a
thorough
examination of
my
argument.
Either there
is
an error
in
my work,
or
Perrin's
suspended
substance
has
a
larger
volume in
the
suspended
state
than Perrin
believes.
The
matter is
also
important
because
of Perrin's
principal
study,
in which he
worked
with similar
suspensions.[6]
I have
an
idea about
a
change
in
Lorentz's
force
postulate. Perhaps
the
thing
will
already
have
taken
on
a
tangible
form
when
you
come.
During
the
last few
days
I
was
completely occupied
with
the Perrin
business
so
that
I
had
no
time
for
anything
else. I
have discovered
a
method
for
the determination of
specific
heats
of
gases
with
diatomic