The secular instability of slightly viscous magnetic Maclaurin spheroids

We show that the instability induced by viscosity, at the point of bifurcation where the Jacobi ellipsoids branch off from the sequence of Maclaurin spheroids, is not inhibited by the presence of a magnetic field. It has already been shown that a toroidal magnetic field leaves the point of bifurcation unaffected, whereas a magnetic field along the axis of rotation pushes the point of bifurcation to eccentricities higher than the value that obtains in the absence of a magnetic field.