Clocks such as this one were called “Mercury” because they used sealed vials of mercury to compensate for changes in the pendulum.
I had a question from Deb, and it is a question that is way over my head, but here we go. Bear with me because the physics of anything is not my strong suit.
Deb writes me, “My grandmother had a Mercury clock. It was a famous brand, so ‘Mercury’ was not the brand name.”
Why did she call it “Mercury?” This is because these clocks, usually called regulators, did contain sealed vials of mercury. And if it happened to break. you had a problem.
Regulator clocks have pendulums that slow down in the summer and speed up in the winter. These antique regulator clocks had metal pendulums, with a weight (I am sure you have seen that). And even though you might not be able to see it, the length of the pendulum gets longer in the summer, which lowers that weight (the center mass) of the pendulum. And you end up with a slower timepiece.
A little vial of the dangerous heavy metal mercury compensated for the change in the pendulum. Two little sealed vials of mercury are sometimes spotted on the pendulum itself, and the level of mercury would rise with a temperature increase, which compensates for the summer lengthened pendulum.
The regulator 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.
This type of clock was invented in the 18th century by two Englishmen (1760-1780), and the great thing about these clocks was the accuracy.
They run with a swinging pendulum that had compensation in the form of one or two mercury vials, so they were the most accurate clock heretofore. Even though they were invented in England, the English didn’t fall for them with the same fervor as the Germanic folks did, and by the 19th century, the Viennese Regulator was the clock of choice. It was in just about every train station.
Gustav Becker was the most celebrated Vienna Regular clockmaker, and his carved walnut wall mounted regulators were ubiquitous 1850-1890. If you have a good one, it can be worth in the $800 range.
The trouble was that back in the 19th century, if your clock ran slower or faster, someone in the household could open the sealed vials of mercury and add more or take out some drops. And perhaps at that time, the man of the house who was doing the fiddling with the clock may not have known that mercury is toxic!
Thus, American clockmakers who made those wall-mounted regulators for, say, the office, were interested in saving money. Therefore, the mercury in the vials was replaced by steel slugs. Thus, the more expensive clocks with four sides of beveled glass and pendulums with little weights could still hold mercury.
Many of the early crystal regulator clocks were fitted with mercury compensated pendulums. All of the French clocks were.
The clock is called a “crystal regulator” because it has glass on all four sides and is driven by a swinging pendulum that is weighted. (In this case, all the glass is beveled.)
The pendulum is the regulator and is in this clock. The pendulum contains two glass vials with mercury. If damaged, these glass vials must be replaced with faux ones as mercury is no longer readily available.
American-made crystal regulators used plated, or very highly polished steel slugs inserted into glass tubes to simulate this look.
Here are a couple great websites if you love clocks: ClockHistory.com, and the Virtual Museum “National Watch and Clock Museum (google.com/maps/@40.0369878,-76.5019409,2a,75y,59.53h,82.13t/data=!3m7!1e1!3m5!1scvTUtu0U4fYmDxpbbomwPg!2e0!3e2!7i13312!8i6656).
My favorite website is the Detex Watchman’s Clock Album (watchclocks.org), where the story of watchmen’s clocks is told and illustrated. These are clocks used to make sure the watchmen (guards) were watching in the places they should be at the correct time. They recorded time and place in the 19th century on this little strange looking portable clock with record-keeping notches.
And finally, a funny thought: Those of us who have grown up with digital timepieces might not know what the term “Quarter to” means! Yes, we might understand 11.45 and not quarter to twelve. And the clock face might go the way of the Regulator clock that uses mercury for accuracy.
Dr. Elizabeth Stewart’s “Ask the Gold Digger” column appears Saturdays in the News-Press.
Written after her father’s COVID-19 diagnosis, Dr. Stewart’s book “My Darlin’ Quarantine: Intimate Connections Created in Chaos” is a humorous collection of five “what-if” short stories that end in personal triumphs over present-day constrictions. It’s available at Chaucer’s in Santa Barbara.
