So that if the sphere is placed in a magnetic field the force acting upon it is the same as that on a current
.
When the sphere is moving with a uniform velocity
, equations (3) become
whence
where
is the velocity of propagation of electrodynamic action through the dielectric. If we put
this equation becomes
With similar equations for
and
, we see that a solution of these equations is
where
is a constant. Since, if
,
and
we have
Similarly
and