Seth Thomas Number 19, eight-day regulator with glass double-vial mercury pendulum at the California State Railroad Museum in Sacramento.The Santa Fe Time Department had charge of many of these excellent clocks for very accurate timekeeping. I looked at two, hanging side by side in the dispatcher’s office in Temple, Texas about 50 years ago when they were being sold off. I really wanted one, but even then the price tag was $3,500.
The mercury pendulum was used on some very accurate clocks for temperature compensation (as ambient temperature rose, the pendulum rod expanded, but so did the mercury level).
Much more on railroad timekeeping at http://RailroadGloryDays.com/RailroadTime