DOC.
23
169
Following
the usual
approach,
we now
seek to
determine the
"longi-
tudinal"
and
"transverse"
masses
of the
moving
electron.
We
write the
equations
(A)
in the
form
[40]
ßß3
=
el
=
el',
=

Y
~
JN
=
eY',
ßß
£$
=

Z
+
|
M =
eZ
and note
first that
eX', eY', eZ'
are
the
components
of the
ponderomotive
force exerted
on
the
electron,
as
observed in
a
system co-moving
at
this
instant with the electron
at
the latter's
speed. (This
force
could
be
measured,
for
example,
by
a
spring
balance
at rest
in the last-mentioned
system.)
If
we
simply
call this force "the force exerted
on
the electron,"
and
maintain the
equation
[41]
Numerical
value
of
mass
x
numerical value
of acceleration
=
numerical value of force,
stipulating, in addition, that the accelerations
be measured
in the
system
at
rest
K,
we
obtain
from
the
above
equations
Longitudinal
mass
=
ä
1
-
v
V
7
Transverse
mass
=
iL
v
V
Of course,
with
a
different definition of force
and acceleration
we
would
obtain different numerical values for the
masses;
this
shows
that
we
must proceed
with
great
caution
when
comparing
different theories
of
the
motion of
the electron.
[42]
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