The parametrically maintained Foucault pendulum and its perturbations

A Foucault pendulum may be maintained indefinitely by parametric excitation, but as a consequence of imperfections in its construction, seismic noise and other perturbations it is liable to precess at other than the ideal rate. It has been suggested by Braginsky et al. (Phys. Rev. Lett. 53, 863 (1984)) that the disturbing factors might be reduced to such an extent that the Thirring-Lense effect of General Relativity could be verified. The present analysis reveals serious problems in addition to those they considered, but indicates how parametric excitation helps to overcome them. Nevertheless their assessment of the chance of success reflects an optimism that the present author cannot share.