Externally: large cream coloured cylinder, top of it contains the eye-piece, measuring screw, adjusting & reading terminals, internal parts are exposed for observation above the cylinder; "zero-length" spring at approximately 45° angle to the vertical attaches to a beam with a small mass at the attaching end & at the other end, a cylinder housing the shock eliminating spring. This instrument is a Lacoste and Romberg gravity meter, used to take relative gravity measurements between stations. The gravity meter balances the force of graviy on a mass in the specific gravitational field against the elastic force of the spring. The zero-length spring postioning causes significant mechanical magnification hence a small change in gravity causes a significant beam displacement, which is measurable. Adjustment of the spring is accomplished using the measuring screw. Without a mass attached, the zero-length spring (obtained by pre-stressing the spring in winding) is a finite length and an initial force is required before the coils begin to separate. The zero-length and the shock eliminating springs completely suspend the gravity response -system, i.e. the beam and mass, protecting the delicate instruments from nearly any shocks except those that damage the housing itself. The cylinder is insulated with a foam-like material and as temperature flucuations can cause changes in the measurements, has a temperature control device. Station gravity is generally repeatable to better than 0.1 mgal. It appears that gravity meters using these basic principles are still in fairly common use today. Lacoste and Romberg have also developed gravity meters for use underwater, shipborne, and in boreholes (much smaller systems).
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