418
DOCS.
408,
409 DECEMBER
1917
408.
To Felix
Klein
Berlin,
5
Haberland
St.,
15
December 1917
Esteemed
Colleague,
I
am
returning
to
you your
second lecture
notebook,
which
I
obtained
from
our colleague
Sommerfeld
a
few
days ago,
with
many
thanks.[1]
It
does
seem
to
me
that
you
are
very
much
overestimating
the
value of
purely
formal
approaches.[2]
The
latter
are
certainly
valuable when it
is
a
question
of
formulating definitively
an
already
established
truth,
but
they
almost
always
fail
as
a
heuristic tool. Thus
I
am
convinced
that the
covariance of
Maxwell’s
formulas
under
transforma-
tion
according
to
reciprocal
radii
can
have
no
deeper significance; although
this
transformation
retains
the
form of the
equations,
it
does
not uphold
the
correla-
tion
between coordinates and
the
measurement
results from
measuring
rods and
clocks.[3]
In
great
respect, yours truly,
A. Einstein.
409. To
Wilhelm von Siemens
Berlin, 5
Haberland
St.
[before
16
December
1917][1]
Highly
esteemed
Privy
Councillor![2]
At the
meeting
of
the
Board of Directors and Board
of Trustees[3]
we
resolved
to make
an
announcement
about the
K.
W.
Institute
through
public
notice.
I
drafted the
notice with Mr. Planck and
Mr.
Harnack and have submitted it for
printing to
the
newspapers
and
periodicals
we
had
selected.[4]
Meanwhile,
I have
paid
and recorded
the
costs
that
arose
out of
this and
other
miscellaneous minor
purchases.
I
think
that, toward
achieving
the
simplest
possible accounting,
it
would be beneficial
if
small
sums were
put
regularly
at
my
disposal
for
the
defrayal
of
running
disbursements.
It
would
probably
be
best
for
me
to have
an
Institute
cashbox at
my
home
containing
a
few
hundred
marks
and
to
render
an
account of
it
at
specified
intervals.[5]
Furthermore, I
would
like to
request
that
a
secretary
be
granted
me
for
three
half
days
per
week. As
compensation
I
am
thinking of 50 M
a
month.
Very respectfully,
A.
Einstein.
P.
S.
Should
I
be able
to
turn elsewhere for such small
matters,
I
kindly request
that
you
inform
me
accordingly.