DOC.
52
339
Doc. 52
ON
THE PONDEROMOTIVE FORCES EXERTED
ON
BODIES
AT
REST
IN
THE ELECTROMAGNETIC
FIELD
by
A.
Einstein
and
J.
Laub
[Annalen
der
Physik 26
(1908):
541-550]
In
a
recently published
study1
Mr.
Minkowski
presented
an
expression
for
the
ponderomotive
forces
of
electromagnetic
origin
that
act
on
arbitrarily
moving
bodies. If
one
specializes Minkowski's
expressions to
isotropic,
[2]
homogeneous
bodies
at
rest,
one
obtains for the
X-component
of the force
acting
on a
unit
volume
+
'
[3]
(1)
where
p
denotes
the
electric density,
s
the
electric conduction
current,
(B
the electric field
strength, and ©
the
magnetic
induction. This
expres-
sion
seems
to
us
not
to
be in
agreement
with
the
electron-theoretical picture
for the
following
reasons:
While
a body
traversed
by an
electric
current
(conduction
current)
experiences
a
force
in the
magnetic
field,
according
to
equation (1)
this
would not be
the
case
if the
body
in
the
magnetic
field
were
permeated
by a
polarization
current (dV/dt)
instead
of
a
conduction
current. Thus, according to Minkowski
there exists
here
a
difference in
principle between
a
displacement current and
a
conduction
current
such
that
a
conductor
cannot
be
considered
as a
dielectric with
an
infinitely
large
dielectric
constant.
In
view
of this
state
of
affairs, it
seems
to
us
that it
would
be
of
interest
to
derive the
ponderomotive
forces for arbitrary
magnetizable
bodies
on
the basis of the electron
theory.
We
present
here
such
a
derivation,
though
restricting ourselves
to
bodies
at rest.
1H.
Minkowski,
Gott.
Nachr.
(1908),
p.
45.
[1]