DOCS.
581,
582
JULY
1918
607
of all for Lorentz
transformations, not[ably]
such linear coordinate
transforma-
tions for which
the
planes
=
C
cut
the
cylinder
into
“cross
sections”
;
thus the
Jo's
can
be defined
by integrals.
For
other
linear coordinate
transformations,
by
contrast,
the
values for
Ja
are
defined
by
the
vector
character
of
the
Ja’s!-
As
you
see,
I
have
gone
through
the
same
stages
as
in
your
letters,
only
that,
owing
to
the
restrictive
precondition
I
placed
at
the
start,
everything
could
be
formulated
more precisely.[9]
I
wonder whether
the restriction
is
necessary
for
the
validity
of
the
theorem?[10]
In
the
case
where
the limitation
is
valid,
do
J1, J2,
J3
in
the
original
coordinate
system
also
vanish,
hence does
the
vector
J
have
the
orientation
of
the
cylinder
enclosing
the
world
tube?[11] I
have not
yet
formed
an
opinion
on
either
of these
points.
I
was
able to
hand
your
e[steemed]
postcard
on
to Mr. Humm[12]
right
away
on Monday.
I
am now
reading Weyl
with extreme
interest.[13]
With best
wishes for
a
pleasant stay
in
the
country,[14]
yours truly,
Klein.
582. From Friedrich Adler
Stein-on-the-Danube, 6
July 1918
Dear
Friend,
It has
been almost
one
year
since
I
wrote
you,
but
I
have been
thinking
of
you incessantly,
for
I
was
occupied
the
whole time
with
relativity
theory.
Now
the
work
is
finally
finished and
I
am
very eager
to know
what
you say
to
it.[1]
I
know
that
you
are so
convinced of the correctness of
your
foundations
that
you
do
not
expect anything
from
further
discussions of it. And
yet
I
would like
to
burden
you
with
the
perusal
of
my book,
for
I
imagine
now
having really
caught
Ariadne’s thread,
leading
to
a
compelling
derivation of
the
necessity
for
a
preferred
reference
system
from
your
transformation
equations.
The
crux
of
the
matter
had
long
been clear to
me,
but
it took
quite
some
effort
to
work out all of
its
consequences
in order
to
make it
convincing
to
others
as
well.
Today
I
would
just like
to know where
I
may
send
you
the
work,
or
for how
long
a
mailing
will
still reach
you
in Berlin.
Now I
have
belatedly
received
the
paper by
E.
Budde in
the
Verhandl. of
1914.[2]
There the
“Einsteinian
optical
clock” is
repeatedly
mentioned. Nowhere
in
your
papers
that
I
know
about
does such
a
thing
appear, though.
It
would be
very
interesting
for
me
if
you
could send
me
the relevant article
or
at least
say
where it has
appeared.[3]
Did
you reply
to
Budde’s
paper,
or was
there
otherwise
any
discussion
attached to it? Considerable difficulties
are
naturally
connected