  The energy and momentum densities of the fields of a free electron in a plane
electromagnetic wave include interference terms that are the classical version
of the ``dressing'' of the electron the arises in a quantum analysis. The
transverse mechanical momentum of the oscillating electron is balanced by the
field momentum resulting from the interference between the driving wave and the
static part of the electron's field. The interference between the wave and the
oscillating part of the electron's field leads to a longitudinal field momentum
and a negative field energy that compensate for the longitudinal momentum and
kinetic energy of the electron. The interference terms are dominated by the
near zone, so that as the wave passes the electron by the latter reverts to its
energy and momentum prior to the arrival of the wave.
