DOC.
47
279
d
1
It
M

0T) dw
+
EJT
x
=
0
(15a)
If the electric
masses are
bound to freely
moving
material
points
(electrons), this
equation
becomes
by
virtue of
(11)
d
^(YN

ZM)du)
+
£
\ix
It
=
0
.
(15b)
[45]
In
combination with the
equations
obtained
by
cyclic
permutation,
this
equation expresses
the
principle
of conservation of
momentum
in
the
case
considered here.
Thus
the
quantity
£
=
fix
1

v1
plays
the role of
the
momentum
of the material
point, and
in accordance with
equations
(11)
we
have
[46]
t
=
Kx
as
in
classical
mechanics.
The
possibility of
introducing
a
momentum
of
the
material point is based
on
the fact that in the
equations
of motion the
force,
i.e.,
the
second
term
of
equation (15),
can
be represented
as a
time
derivative.
Further,
one sees
immediately
that
our
equations of motion of
the
material
point
can
be
given
the
form
of
Lagrange's
equations of
motion;
for,
according
to
equations (11),
we
have
d
m
77 =
K
x,
etc.
dx
where
we
have
put
H
=
fic2
1
5
+
const. [47]
The equations
of
motion
can
also
be represented
in the
form
of
Hamilton's
principle
t
1
(dH
+
A)it
=
0
,
t
0