Duality-invariant magnetohydrodynamics and dyons

The theory of magnetohydrodynamics is extended to the cases of a plasma of separate magnetic and electric charges, as well as to a plasma of dyons, respectively. In both these cases the system possesses electric-magnetic duality symmetry. In the former we find that, because of the existence of two independent generalized Ohm's law equations, the limit of infinite electric and magnetic conductivity results in the vanishing of both electric and magnetic fields, as well as the corresponding currents. In the dyonic case, we find that the resulting duality-invariant system of equations are equivalent to those of ordinary magnetohydrodynamics after suitable field redefinitions.