DOC.
44
237
but
only
with
a
principle that (similar
to
the
second
law
of
the
theory
of
heat)
permits
the reduction of
certain
laws
to
others. [8]
2.
Previously,
when
one
did
not rely
on
the
principle of
relativity,
but instead
tried
to
obtain the
laws
of
motion of
electrons
by
electrodynamic
methods,
one
found
it
necessary
to make
more
definite
assumptions
on
the
distribution of
electricity
so
that the
problem
is
not
an
undetermined
one.
The
electricity
was
thought
of
as
being
distributed
over a
(rigid) framework. [9]
It should
be
noted
that the
laws
that
govern
the
motion
of
such
a
structure
cannot
be
derived
from electrodynamics
alone. After all, the
framework
is
nothing
other than the introduction of
forces
which
balance the
electrodynamic
ones.
If
we
view
the
framework
as
a
rigid
body
(i.e.,
one
not
deformable
by
external
forces),
the
problem
of the
motion
of the electron
can
be
solved
deductively
without arbitrariness
only
if the
dynamics
of
the rigid
body
is
known
with sufficient
accuracy.
[10]
If the
theory of
relativity
is
correct,
we are
still far
from
the latter
goal.
For
the time
being,
we
only
have the kinematics
of parallel
translation
and
an
expression
for the kinetic
energy
of
a
body
in
parallel translation,
provided
the
latter
does
not
interact with other
bodies1;
for the
rest,
both
the
dynamics
and
the kinematics
of
a
rigid
body
have at present to be
considered
as
unknown
for the
case
under consideration.
Bern,
14
April 1907.
(Received
on
16
April
1907)
1I
will
soon
show
in
an
article that
the
latter restriction is
essential. [11]