  There is a fundamental difference between the classical expression for the
retarded electromagnetic potential and the corresponding retarded solution of
the wave equation that governs the electromagnetic field. While the boundary
contribution to the retarded solution for the potential can always be rendered
equal to zero by means of a gauge transformation that preserves the Lorenz
condition, the boundary contribution to the retarded solution of the wave
equation governing the field may be neglected only if it diminishes with
distance faster than the contribution of the source density in the far zone. In
the case of a source whose distribution pattern rotates superluminally (i.e.,
faster than the speed of light in vacuo), the boundary term in the retarded
solution governing the field is by a factor of the order of R^(1/2) larger than
the source term of this solution in the limit where the distance R of the
boundary from the source tends to infinity. This result is consistent with the
prediction of the retarded potential that the radiation field generated by a
rotating superluminal source decays as 1/R^(1/2), instead of 1/R. It also
explains why an argument based on the solution of the wave equation governing
the field in which the boundary term is neglected, such as Hannay presents in
his Comment, misses the nonspherical decay of the field.
