  Recently there have been suggestions that the Lorentz force law is
inconsistent with special relativity. This is difficult to understand, since
Einstein invented relativity in order to reconcile electrodynamics with
mechanics. Here we investigate the momentum of an electric charge and a
magnetic dipole in the frame in which both are at rest, and in an
infinitesimally boosted frame in which both have a common velocity. We show
that for a dipole composed of a magnetic monopole-antimonopole pair the torque
is zero in both frames, while if the dipole is a point dipole, the torque is
not zero, but is balanced by the rate of change of the angular momentum of the
electromagnetic field, so there is no mechanical torque on the dipole.
