We prove the existence of a generalization of Kelvin's circulation theorem in
general relativity which is applicable to perfect isentropic
magnetohydrodynamic flow. The argument is based on a new version of the
Lagrangian for perfect magnetohydrodynamics. We illustrate the new conserved
circulation with the example of a relativistic magnetohydrodynamic flow
possessing three symmetries.Comment: Invited talk at IARD 2000, the Second International Conference on
Relativistic Dynamics, Bar-Ilan University, Israel, 26-28 June, 2000. To
appear in the proceedings in a special issue of Foundations of Physic
