658
DOCS.
627,
628
SEPTEMBER
1918
bookwhich
could,
of
course,
have remained
completely
unmentionedis that
I
had
naturally
misunderstood
Riemann and
Helmholtz.[11]
It
is
completely beyond
him
that
he could have
misunderstood various
things
himself. For
inst.,
he
thinks
that the
world lines
are
the
shortest
(rather
than the
longest)
lines.
I
was
very
annoyed
about this
gentleman
and
was
thus
doubly
pleasantly surprised upon
receiving
such
an
amicable
letter
from
you.
I
am
also
sending you my
lecture
on
kinematics.[12]
But
you really
are on
my
mailing
list. Should
you
happen
to find
the other
copy,
please
be
so
kind
as
to
return
one.
I
hope
that
you
will take
a
glance inside,
it
is
one
of
my
best
works,
the
content
perhaps
even
useful in
physics,
if
only
in
the broader
consequences.
So, now
I
really
have written
you
a
long
letter, and
you will
be
glad
that
it
is
now
coming
to
an
end.
With best
regards, yours very truly,
E.
Study.
628. To
Friedrich
Adler
[Berlin,]
29 September 1918
Dear
Friend,
Many
thanks
for
the
nice and concise
letter.[1]
The
good
part
about
these
grim
times
is
that
they
compel brevity.
So
let’s
go!
The reflections of
§38[2]apart
from
the introductory
criticismis, in
my view, thoroughly
correct
including
the
resulting
final
equation
(126).
But
you
are
not allowed
to offer
the
choice
between
either
equation
(126)
or
(113).
For,
since
the
constant
a
can
still
depend
arbitrarily
on u,
both
equations
are
entirely equivalent.
Your criticism
at
the
top
of
page
221
would be valid
only
if the
E''s
signified lengths
measured in
S,
which
is
not
the
case,
however:
E'E'0 is
the
difference between
the
two abscissas measured
in
K, relative to
a
specific
time
T
of
K
(that
is, a
time
common
to
both
points).[3]
I
fully
maintain
my
earlier
consideration, although
I
must
admit
that
it
was a
bit
more
impractical.
Now
the
remaining
main issue
is
the determination
of
the
factor
l
in
the
equations
x1
=
lß\x

ut)
y'
=
ly
2!
=
lz
I'
=
lß(t
^
(1)