266
DOCS.
363,
364
FEBRUARY
1912
current
behind
an
obstacle
exactly
as
it
actually
looks.[2]
It
is
a
pity
that
we
do
not
understand
how it
is
formed. It
is
a
most
peculiar
thing:
the
already
formed
current
can
be
calculated
from the
theory
of nonviscous
liquids,
but
its
formation can't.
So
then
we
think of
forces,
of
course.
Besides,
we
have
a
large
wind
tunnel for
testing surfaces,
propellers,
etc.
We have
now
thought
up a very
interesting
project:
We want
to
do
Meyer-like
fluctuation
measurements
on currents,[3]
and thus
obtain information
on
the
structure
of
the
hydrodynamic
field;
the measurements
are
not difficult to
do,
but
to
conclude
something
from
them
is
a
ticklish
matter. I meet
frequently
with
Meyer;
he has
a very good
head, and
is
good
at
bringing up
problems
and
devising
interesting
experiments.
At the
moment I
am
struggling
with
a
little note of
yours
in which
you
develop
a
theory
of fluctuations
in
instruments.
I
would like
to
elaborate
on
it
in view
of
the
Meyer-Campbell discussion.[4] I
found
a
serious
error
in
the latter's
calculations.
You
probably already
know
that
Meyer
is
going
to
Tübingen.[5]
I
am very sorry
about
it,
because not much will
then
go
on
in
physics.
To be
sure,
Reissner[6] is
interested
in
a
lot
of
things
and has
a
sharp
and critical
mind;
a man
to
your
taste,
I believe,
completely
independent to
the
point
of
sticking doggedly
to
the
ideas
he has
developed,
and
up
to
date
with
modern
thought.
By
contrast,
Stark[7] is
totally
insane, he kicks
up
a row
with
everybody,
and
recently
even
kicked
Meyer
out for
the
sole
reason
that
Meyer
mentioned
some nonsense
communicated
to
him
orally by
Stark
in
only one,
instead of
in
two
of
his
articles.[8]
I
still
sometimes
ponder
our
dear
h and believe in time
atoms;
but
nothing
really
clever has
so
far occurred
to
me.
I hope
that
you
have
fared better
and that,
perhaps,
you
see a
ray
of
hope
again.
I
am eagerly looking
forward
to
the
publication
of
the
Brussels
proceedings.[9]
Haber
is
doing
the
most
amazing
tricks with the
h.[10]
Have
you
read that Hondros
has become
Ordinary
Professor of
Physics
in
Athens?[11]
I
hope
that
all
of
you
are
well and
cheerful,
and
happy
about Zurich.
My
best
regards
to
all who still remember
me!
Your
L.
Hopf
364. To
Ludwig
Hopf
[Prague,
after
20
February
1912][1]
Dear
Mr.
Hopf:
Your
letter[2] just
arrived and
stirred
up anew my feelings
of
guilt
toward
you.
But
I should be excused
on
the
grounds
that
I
work
like
a
horse,
even
though
the
cart does
not
always move very
far
from the
spot.
But
a
few
things
have
gone
well. I derived the
law
of
photochemical equivalents
by way
of
thermodynamics,
without
quanta.[3]
I
have
now
derived
the
theory
of
gravitation
for
the static field in
a
completely
rigorous
manner.[4]
The
thing
is
stunningly
beautiful
and
amazingly simple.
Abraham's
theory is