318 DOC.
328
APRIL
1917
328. To
Felix Klein
Berlin,
21 April
1917
Highly
esteemed
Colleague,
If
presently
I
weren’t
the
slave of
a
book taken out of
the
library,
I
would
have
already
looked at
the
papers you
mentioned,
not
only your
own
but the
other
two
as
well.[1]
Thus,
however,
I must
allow
another
couple
of
weeks
to
pass.
Grossmann
(I believe)
had
the little
book
by Wright
when
we were working
to-
gether
on
relativity
4
years
ago.[2]
I have
already
had Batman’s
paper
in
hand but
must confess
that
I
cannot
quite
imagine
it
possible
that
any physical meaning
be
afforded to
substitutions
of
reciprocal
radii.[3]
Not
only
does the
Lorentz trans-
formation
leave
the
velocity
of
light invariant,
but
the coordinates of coordinate
systems
related
in such
a
way
have
a
simple physical meaning
as
measurement
results
from
measuring
rods and
clocks.
This latter
quality
is certainly
lost in
Bateman’s transformations.[4]
I
am
very
much
looking
forward to
your lectures,
which
you
have
promised
me.[5]
I
shall
pass
them
on
to Sommerfeld
as soon as
I
have received and
studied
them.
Probably-knowing
me-nothing
will
come
of
my
article for
the
encyclo-
pedia.
I
was
cautious
enough,
if
I
recall
correctly,
not
yet
to
give a
positive
answer
to
our
colleague
Sommerfeld.[6]
Hilbert’s second
relativistic
paper
interested
me
very
much.[7]
Just the
geodet-
ic reference
system
introduced
there,
which
is characterized
by
g14 = g24 = g34
=
0
and
g44
=
1,
does not
seem
acceptable
to
me.
For
it
can
be
demonstrated
through
examples
that
this
system
does
not
preserve
the
uniqueness
of the
assignment
of
coordinates
to
space-time points.
This
stems
from
the
temporal
geodetic
lines
intersecting
one
another.
However,
it would not be inconceivable
that
otherwise
definable coordinates
existed,
which would
simplify
the
relations.
Although
the
coordinate
choice
I
made
in
some
papers according
to
the
condition
g
=
-1
is
natural
in
some
cases,
it limits
the
choice
just
a
little
(only
one
limiting
condition
rather than
four).[8]
With best
regards,
I
am
yours truly,
A. Einstein.
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