Abstract: Three sets of laser angular sensors or masses, corresponding to three angularly disposed sensing planes, are mounted on a common instrument block. A compensating mass, which may be a fourth sensor, is also mounted on said instrument block. Said sensors or masses are supported for angular dithering about predetermined axes. The amplitudes, frequencies and phases of the dithering are adjusted, either by being actively directly driven or by passive mechanical coupling, to balance momenta and torque between said dithered masses. The ditherings of the masses of the sensors are of amplitude and frequency to avoid lock-in of said sensors. One, two, three or four dither mechanisms selectively may simultaneously be energized. The driving dither mechanisms may be switched from one mass to another or from one permutation and combination of masses to another. The switching may be a timed sequence, a random sequence, or a commanded sequence.

Abstract: Apparatus for containing a ferro-fluid within a reservoir of ferro-fluid using a pair of ferro-magnetic members adjacent each other and having opposing surfaces shaped as segments of surfaces of revolution, including magnetic apparatus for producing magnetic flux across the gap between the opposing surfaces. The surfaces diverge, and the greater magnetic flux density at the closely spaced edges of the pocket formed by the surfaces hold the ferro-magnetic particles of the ferro-fluid in that region. The volume between the two opposing surfaces is adequate to accommodate the thermal and pressure expansion and contraction of the fluid. The spacing between opposing members at the edge of farthest advance of the fluid is sufficiently small to allow the surface tension of the fluid to hold the fluid.