  Following Prendergast we study the relativistically expanding electromagnetic
fields generated by an axisymmetric explosion of magnetic energy in a small
volume. The magnetic field expands uniformly either within a cone or in all
directions and it is therefore accompanied by an electric field. In the highly
conducting plasma the charges move to annul the electric field in the frame of
the moving plasma. The solutions presented are analytical and semi-analytical.
We find that the time-scale for the winding up of the initial magnetic field is
crucial, as short time-scales lead to strong radiant fields. Assuming a
magnetic field of $10^{13}Gauss$ emerging from a magnetosphere of $10^{9}cm$ we
end with a jet when confined by a pressure environment that falls more slowly
than $r^{-4}$. The jet carries energy of $10^{51}erg$, which is mostly due to
differential rotation at the base.
