DOC.
45
239
rigidly electrified
body,
and in
the
second
case
it consists
of
a
number
of
uniformly
moving mass
points which
do
not
exert
any
forces
on
each
other.
Before
I start
with the investigation, I
must
insert here
a
remark
on
the
presumed
range
of
validity
of
Maxwell's
equations
for
empty
space
so as
to
meet
a
naturally
arising
objection. In
earlier
papers
I
showed
that
our
present electromechanical world
view
is
not suited
for
explaining
the entropic
properties
of
radiation
and
the
laws
governing
the emission
and
absorption
of
radiation
and
those
governing
the
specific
heat; rather, it
seems
to
me
necessary
to
assume
that the
nature of
any
periodic
process
is
such
that
the
conversion of
energy
can
only proceed
in certain
quanta of
finite
magnitude
(light quanta),
i.e., that the
manifold
of
processes
possible in reality is
smaller than the manifold of
processes
possible
according
to
our
present
theoretical
views.1
In
particular,
we
would
have
to
imagine
that
in
a
radia-
tion
process
the instantaneous
electromagnetic state
in
a
region
of
space
is
completely
determined
by a
finite
number
of
quantities--in
contrast to
the
vector theory
of radiation.
But
as
long
as we
do not
possess
a
picture
that
corresponds to
the
requirements
mentioned, it will
be
natural
to
use
the
current
theory
for all
problems
not
concerned with
entropy
relations
or
conversions
of
elementary
small quantities of
energy
without
having
to fear
that
we
will
thereby
arrive
at
incorrect results.
I
can
illustrate
most
graphically
how
I
see
the
present
situation
regarding
these questions with the
following imaginary
case.
Let
us imagine
that the molecular-kinetic
theory
of
heat
has not
yet
been
propounded,
but that it
has been
demonstrated with
complete
certainty
that the
Brownian motion
(motion
of
particles
suspended
in liquids) is
not due
to
any
external
supply
of
energy,
while it is
clearly
recognized
that these
motions
cannot
be
explained
with
the
help
of
mechanics and
thermodynamics.
In
such
a
situation
one
would
rightly conclude that
a
radical
change
of
theore-
tical principles
must
take
place.
In
spite of
that,
nobody
would shrink
from
applying
the fundamental
equations
of
mechanics and
thermodynamics
to
handle
problems
not
related
to instantaneous
states
in small
regions
of
space.
In
this
sense,
in
my
opinion,
we
can
confidently
base
our
considerations
on
Maxwell's equations.
1A.
Einstein,
Ann.
d.
Phys.
17 (1905):
132; 20
(1906):
199;
and
22 (1907):
180.
[3]