  At a generic point in the moduli space of vacua of an N=4 supersymmetric
gauge theory with arbitrary gauge group the Higgs force does not cancel the
magneto-static force between magnetic monopoles of distinct charge. As a
consequence the moduli space of magnetically charged solutions is related in a
simple way to those of the SU(2) theory. This leads to a rather simple test of
S-duality. On certain subspaces of the moduli space of vacua the forces between
distinct monopoles cancel and the test of S-duality becomes more complicated.
