DOCS.
408,
409
JUNE
1912 309
to
Wien's end of
the
radiation
law and
to
the
law of
quanta.
Essentially, one
needs
only
the
assumption
that the
chemically
active amount
of radiation absorbed
per
unit
time
is
proportional to
the
density
of the monochromatic radiation.
We
are
doing fine,
and all of
us are
happy
about
Zurich.[8]
The
fierce
Weber
has
died
there,
so
that
it will be
very
pleasant
from
a
personal point
of
view
as
well.[9]
I
am
only sorry
to have
to
say
good-bye
to
my colleague
Pick,[10]
with whom
I've become
very
good
friends.
Sangue
non e
aqua
[blood
is
thicker than
water],
as
the Italians
say!
I
wish
you
much luck with
your
sun-venture,
but
I
do not
quite
understand what it's
all
about.
What,
in
fact,
do the
colleagues say
about the
relinquishing
of the
constancy
of
the
speed
of
light?[11]
Wien
seeks
to help
himself
by disputing
the
gravity
of
energy.[12]
But this
is
untenable ostrich
policy.
With
best
regards to
you
and
your
parents,[13]
your
[...][14]
A.
Einstein
409.
To
Paul Ehrenfest
[Prague,
before
20
June
1912][1]
Dear
Mr.
Ehrenfest:
I
congratulate
you
on
the
news
from
Lorentz![2] Apart
from
yourself, no one
would
be
happier
than
I
if
you
were
called
to
Holland.
You
are one
of
the few
theoreticians
who has
not
been robbed of
his
common sense by
the mathematical
contagion!
You
are
right
about
reflection.[3]
There
is
no
first-order
effect. I have
established
this
beyond any
doubt. Don't
you
think that
one
should be able to find
a
second-order
effect
in the
light
of
a
canal-ray
tube?
It
is
of the order of
magnitude
of
10-4.
Give
some
thought
to this
matter!
Your
note[4]
did
not
annoy
me
in the least! On
the
contrary.
Such
arguments
are
quite
familiar
to
me
from
pre-relativistic
times.
I
knew well
that the
principle
of the
constancy
of the
velocity
of
light
is
completely
independent
of the
relativity
postulate,
and
I
considered what
is
more
probable,
the
principle
of
the
constancy
of
c as
demanded
by
Maxwell's
equations,
or
the
constancy
of
c exclusively
for
an
observer
sitting
at
the
light source.
I
decided
on
the former because
I
was
convinced
that
all
light
is
defined
by
frequency
and
intensity
alone,
completely
independently
of whether
it
comes
from
a
moving or
resting
light
source.
Further, it did not
occur
to
me
to
consider that deflected
radiation
might
behave
differently
with
regard
to
propagation
from
radiation
newly
emitted
at
the
point
in
question. Complications
of
this kind
looked
to
me
much
more
unwarranted than those that the
new
concept
of
time
brings
in its
train.
In
answer
to
the
question,
"Why
do
the
waves
of
a moving light
source
move
so
asymmetrically,"
the
best
I
can
say
is
that
this has to do with the
definition of
time. As