  The relativistic conservation law involving the center of energy is reviewed
and illustrated using simple examples from classical electromagnetic theory. It
is emphasized that this conservation law is parallel to the conservation laws
for energy, linear momentum, and energy, in arising from the generators of the
Poincare group for electromagnetic theory; yet this relativistic law reflecting
the continuous flow of energy goes virtually unmentioned in the text books. The
illustrations here present situations both where external forces are present
and are absent. The cases of a parallel plate capacitor, a flattened slip-joint
solenoid, and two interacting charges are included.
