DOC. 40 ON KOTTLER'S PAPER
239
This is
especially
true
of
the
concepts
TvaB =

{aBv}
(components
of
the
gravitational
field)
and
tav
(energy components
of
the
gravita
tional
field).
The introduction
of
these
names
is in
principle unnecessary,
but at least
for the time
being
and
in
order to maintain the
continuity
of
ideas,
I do not think
they
[p.
642]
are
worthlessand
that
is
why
I
introduced these
quantities even though they
do not
have tensorial character. The
principle
of
equivalence, however,
is
always
satisfied
when
equations are
covariant.
5.
It is true that the
price
I had to
pay
for the
general
covariance
of
the
equations
was
the abandonment
of
ordinary
time measurement and Euclidean measurement
of
space.
Kottler
believes he
can
do without this sacrifice. But
already
in
the
case
of
the
system
K',
considered
by him,
which is accelerated relative to
a
Galilean
system
in the
sense
of
born,
one
has to abandon the
ordinary
measurement
of
time. The
[5]
point
of
view
of
the
theory
of
relativity suggests
then,
obviously,
also the need to
abandon the
ordinary
measurement
of
space.
Herr
Kottler will
certainly
convince
himself
of
this
necessity
if
he
tries
to
execute
in
a general
manner
his
intended
theoretical
plans. [6]
October
1916