What a strange pendulum indeed. Why would it have both a mercury jar and a bimetallic gridiron? I've read that many clocks that started out as gridiron were later modified to be mercurial because the latter system is better, but if this one was so, why would they reuse the old gridiron instead of making a new simpler rod? Also, gridirons normally have either four brass and five steel rods, or three steel and two zinc, combinations that are dictated by the ratios of the materials' thermal expansion coefficients. How would two brass and one steel even work? I wonder then if this was originally an Ellicott compensated pendulum, which does use a center steel and two marginal brass rods, but with a special bob with two levers that raise the bob when the expanding brass pushes on them. And then somebody later would have decided to modify it to to mercury, but kept the original rod just to preserve the clock's original look? commons.wikimedia.org/wiki/File:Ellicott_pendulum.png
Beautiful clock.
What a strange pendulum indeed. Why would it have both a mercury jar and a bimetallic gridiron? I've read that many clocks that started out as gridiron were later modified to be mercurial because the latter system is better, but if this one was so, why would they reuse the old gridiron instead of making a new simpler rod?
Also, gridirons normally have either four brass and five steel rods, or three steel and two zinc, combinations that are dictated by the ratios of the materials' thermal expansion coefficients. How would two brass and one steel even work?
I wonder then if this was originally an Ellicott compensated pendulum, which does use a center steel and two marginal brass rods, but with a special bob with two levers that raise the bob when the expanding brass pushes on them. And then somebody later would have decided to modify it to to mercury, but kept the original rod just to preserve the clock's original look?
commons.wikimedia.org/wiki/File:Ellicott_pendulum.png
I think you may be right that it was originally an Ellicott. It's a mystery!