Mercury pendulum vials.
Many of the early crystal regulator clocks were fitted with mercury compensated pendulums. I believe that all of the French clocks were. The American made crystal regulators used plated, or very highly polished steel slugs inserted into glass tubes to simulate this look. I have seen some American regulators with mercury vials but I believe that these were retrofitted at a later date.
The pendulums were designed to compensate for temperature variations. As metal gets warm it expands down. The metal (mercury) sealed in the vial has nowhere to expand but up. This was supposed to keep the center of oscillation constant.
As a result of very rough handling, or sometimes dropping, the vials would break at the sealing end where the glass is the thinnest. Once broken, replacements could not be purchased from supply houses and would have to be custom made. Since this is a very difficult item to find clocks were often fitted with the new "faux" mercury pendulums that are readilly available (although not cheap).
I am now able to reproduce these mercury vials.
The photo below shows one of the new mercury type pendulums that originally came with the slugs, but now contains real mercury vials
Price per set of two.
$125 up to 9 mm diameter
$135 up to 11 mm diameter
$150 up to 15 mm diameter
This photo shows an antique original pendulum being fitted with wials.
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Medford, NJ 08055
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