ON THE LIMITATION IMPOSED BY GRAVITY ON MEASUREMENTS OF THE CRITICAL VISCOSITY OF A PURE FLUID

Measurements of the viscosity of a fluid by means of a parallel plate torsional oscillator are conventionally limited to a plate separation that is much larger than the viscous penetration depth of the fluid co ntained between the plates. Here we demonstrate that, in principle, us eful measurements can be carried out in the opposite regime where the thickness is smaller than the penetration depth. An alternative method , described in the last part of this paper, for alleviating the restri ction imposed by the density stratification that results from the eart h's gravity, is to use electrostriction, rather than the inertial forc e, to drive the fluid between the plates.