DOC.
52
341
If
one
imagines
that the
above
expression
is
formed
for
and
summed
over
all
dipoles in
the unit
volume,
one
obtains,
taking
into
account
the relation
the
equation
(4)
5lx
lr-y,
X
d£
x
Ux
+
93
x
d£
V
oy
+
%
~Tz
X
If
the algebraic
sum
of
the
positive and
negative
conduction electrons
does
not
vanish,
then the
expression
(4)
contains
an
additional
term, which
we
shall
now
calculate.
The X-component
of
the
ponderomotive
force
acting
on a
conduction electron
of
electric
mass
e
is e(E. If
one sums over
all
conduction electrons
of
the unit
volume,
one
obtains
(5)
hi
-
I
If
one
imagines
that the
matter in
the unit
volume
is enclosed
by
a
surface
that
does
not
cut
through
any
dipole,
one
obtains
in
accordance with Gauss's
law
and
the definition
of the
displacement
vector ®
J
e
=
div
D
,
so
that
(5a)
^2*
=
div 15.
The X-component
of the
force exerted
by
the electric field
strength
on
the
unit
volume of
the
matter
therefore
equals
(6)
9(8
5
x
^lx +
^2x
^x
üx
x
9(8
+ 93
x
d£
+
93
X
y
dy
^z
Uz
x
+
£
div
D
In
an
analogous
way,
taking
into
account
the relation
div
»
=
0,