274
DOCS.
372,
373
MARCH
1912
correct,
and
I have
corrected whatever
I could
as
best
I
could.
Perhaps
this also includes
the
thing you
criticized.
If
not,
I
am
grateful
for
being
given a
chance to
make further
improvements.
But
I
cannot
guarantee
that
this
is
still
possible,
because about half
of
the book
has
already
been
printed.
However,
a
note could still be
put
in
an
addendum.
I believe
that
you
are
again
in
Zurich[5]
and
am sending
this
letter there.
Yours
very truly,
Walter
König
373.
To
Walter
König
[Prague,
after
11
March
1912][1]
Esteemed
Colleague:
Unfortunately,
I
am
not in
possession
of
Drude's
outstanding
book.[2]
I
only
had
it
on
loan for
some
time
through
the kindness of
a
colleague.
Therefore
I
no
longer
remember the
details.
The
worst
error,
which
occurs
in
several
places
in
the
book,
concerns
the characterization of the
field
of
permanent
magnets.
For
permanent magnets
div
23
=
0
rot
23
*
0
Diagram.
The
lines
are
closed
but
on
the
other hand
div
Ģ
^
0
curl |)
=
0
In
fact,
the
line
integral
of |)
over a
closed
path must
vanish.
Kanal
f
I
-
Linienintegral
j
|
da
=
0.
In several
places
Drude
gives
the
course
of
|i
in
the interior of the
magnet
incor-
rectly.[3]