162
DOC. 224 AUGUST
1910
224.
To Jakob
Laub
Zurich, Saturday
[27
August
1910][1]
Dear
Mr. Laub:
Forgive
me
my long
silence. I have not
gotten
around
to
writing
to
you simply
because
I
did not have
the
time. You would not believe
the
heap
of
personal
responsibilities
that
always
descend
upon
me
and
even
interfere somewhat
with
my
scientific work.
I
did not
get
the
call
to
Prague.
I
was
only
proposed by
the
faculty;[2]
but
because of
my
Semitic
origin
the
ministry
did not
approve
the
proposal.[3]
I will
remain
in
Zurich
during
the entire vacation
and would be
very
pleased
if
you
visited
me.
Sommerfeld
was
recently
here
with
me
for
an
entire week
to
discuss
the
question
of
light
and
some
matters
regarding
relativity.
His
presence
was a
real feast for
me.
He
concurred
to
a
large
extent with
my
views
on
the
application
of statistics.
Also
our
ponderomotive
forces,[4]
which met with
a
poor reception
from
Laue[5]
and
even
from
Wien in
the
Enzyklopädie,[6]
came up
in
the
discussion. But
Sommerfeld
has
now
recognized
that
we are
right,
thanks
to
a very amusing
and
simple special case.
We ask
the
question
whether the
ponderomotive
force
is equal
to
(iH)
or
(iB).[7]
We show
that
in
a
case
in which
H
=
0
and B *
0,
the
force must
inevitably
vanish.
Here
you
see
the front
view
&
the
side view
of
a
steel
disk.
The
disk
is magnetized
in
circular
lines
(remanent
field,
fixed
magnetization).
Suppose
that the
current
flows from
the
center
of the
disk toward its
periphery
according
to
the
scheme shown in
the
side view.
If
this
magnetization (H
=
0
B
=
4ttI) produces
a
force,
then
this
is
the end
of the
principle
of
action and
reaction.[8]
But
Lenard[9]
must be
very
"screwed
up"
in
many
things.
His
recent
lecture about the abstruse ether-business
seems
to
me
almost
infantile.[10] Furthermore,
the
investigation
he forced
upon
you
(Sommerfeld
and
Pockels[11]
told
me
about
it)
borders
on
the ridiculous.
I
am sorry
that
you
must
spend
your
time
on
such idiocies. All
that
my
paper
in the
Archiv[12]
contains
is
a
rather broad
exposition
of the
epistemological
foundations
of the
theory
of
relativity;
it
contains
no
new
arguments
whatsoever and
almost
nothing quantitative. Together
with Mr.
Hopf
I
have
written
two articles
on
the
theory
of
radiation,[13]
the
first
of
which shows
that there
can
be
no
probability
relations between
the coefficients
of the Fourier
expansion
of
a
radiation
vector. I
am
now
writing
a
paper
on
the
opalescence
of
gases
and
liquids.
Quantitative elaboration of
Smoluchowsky's
theory.[14]
I
am
done
with
the
part
that
considers
the
principle.
The
theory is
absolutely rigorous.
I have not
made
any
progress
regarding
the
question
of
the
constitution of
light.
There
is something
very
fundamental
at the
bottom of
it. Mayer
is
carrying
out
an interesting
investigation
on
the fluctuations