A recent theory of Nycander (1996) establishing the analogy between the steady westward drift of geophysical vortices and the precession of a rigid-body (in particular a disc spinning about its symmetry axis) is rederived within a Lagrangian framework. This formulation allows the time-dependent properties (e.g., trajectory, spinetc.) of the rigidbody, represented by three coupled ODEs, to be studied. Numerical results for a variety of initial zonal velocities and latitudes are presented. Typically the trajectory consists of a mean westward precession coupled with periodic behaviour which, in the terminology of rigid-body dynamics, is known as nutation. In the limit that β-plane physics are appropriate, it is shown that the nutation is exactly analogous to harmonic inertial oscillations at the local Coriolis frequency.