278
DOC. 377
MARCH
1912
as
well
as
all
of the other
influences
of the
gravitational
field
on
electromagnetic
processes.
Energy density
=

(S2
+)2)
2
Totally analogous
to
the
energy
c
·
m
of
the
mass
point at
rest.
m
is
the ratio
of
the
point
mass
to
the
mass
of
1 cc
of
water,
thus
defined,
just
like
6,
as
independent
of the
location. Most
interesting
of
all
is
the
theory
of the
gravitational
field
itself, during
the
development
of
which it
turned
out
(that
the
principle
of
equivalence
of
accel.
& gravitation
holds
only
for
oo
small
systems.)
The
equation
of the static
grav.
field
is
cAc
 ^grad2c
=
kc2a,
where
a
denotes
the
mass
density
(+
energy density).
The
second
term
of
the lefthand
side
of
the
equation
is
the
energy
density
of
the
gravitational
field
multiplied
by
c.
This
density
leads
to
a
convergence
of the
gravit.
lines like
any
other
energy density.
I will
send
you
the
papers
as
soon
as
the
slow Annalen has
printed
them.[4]
You
see
that
I
am
still far
from
being
able to conceive
of rotation
as
rest!
Each
step
is
devilishly difficult,
and
what
I have
derived
so
far
is
certainly
still the
simplest
of
all.
Abraham's
theory
has
been created
out
of
thin
air,
i.e.,
out
of
nothing
but considerations of mathematical
beauty,
and
is
completely
untenable.[5] How this
intelligent
man
could
let himself
be
carried
away
with such
superficiality
is
beyond me.
To
be
sure,
at
the
first moment
(for
14
days!)
I too
was
totally
"bluffed"
by
the
beauty
and
simplicity
of
his formulas.
The
thermodynamical
study on
the
photochemical
effect has not
yet
come
out.[6]
It
applies
only
to
the
Wien
region.
Assumptions.
The
decomposition
of
a
molecule
is accompanied
by
the
absorption
of
s,
which
is independent
of radiation
density.
Its
reconstruction
is
accompanied
by
the
emission
of
e,
also
independently
of
the
radiation
density.
Thus,
e can
depend
on
the
temperature
of the
gas
at
the
most. Further,
let the number of molecules
decomp.
per
unit
time
at
a given gas
temperature
be
proportional to
the radiation
density.
There
follows
1.
Wien's rad.
law
2.
s
=
hv.
For nonWien radiation
at
least
one
of
the
assumptions
must be
wrong.
The
matter
with
optical
proper frequencies
in
the infrared
is
by no means as simple as
I wrote
to
you
at
the
time.[7]
Rubens informed
me
that
the existence
of
the two
reflection
maxima
of
zero
is
beyond any
doubt.
It
turns out
that
absorption,
which
is
very strongly
dependent
on
the
frequency,
also
plays an
important
role in
reflection
phenomenon.
Thusunless mechanics
fails in
principlemy
result
should be valid
at
sufficiently
low
temperatures.
The determination of
proper frequency
by
thermal
means
is
rather