Introduction: "Prior analyses of a plasma in a magnetic field have been limited, as far as the writer is aware, to cases in which the relative change in field over the orbital distance and the relative change in ion concentration are both small, or in which the relations have been viewed in a purely hydrodynamical way. The first approach excludes cases which can be of considerable interests, for it fails near a plasma edge. The second loses all sight of the structure imposed by the orbital motions."