Resonance can mean a lot of things, but for our purposes we’re interested in mechanical resonance. Resonance is actually present in all watches – in physics, the term just means the tendency for some physical system to oscillate with greater amplitude at certain frequencies than at others. A feature of resonance is that a relatively small driving force, if it occurs in synch with the resonance frequency of a system, will drive it to progressively greater amplitudes. In something like a swing, it simply means it will swing further.

The back of FP Journe’s Chronomètre à Résonance, showing twin balances beating in resonance.

Now, one resonance associated phenomenon is that if you have two oscillators with the same resonance frequency, and they’re mechanically coupled in some suitable fashion, they will begin to affect each other’s oscillations in all sorts of interesting ways. Depending on how the oscillators are coupled, this can be fascinatingly unpredictable, but in the case of clocks, if you couple two pendulums of the same length through their suspensions, they will begin to oscillate in phase (or 180 degrees out of phase) with each other.

This phenomenon was observed by Galileo, and two horologists of the past (Breguet and Janvier) were noted for having made clocks with double pendulum systems, where two pendulums are suspended from a common mount. The two pendulums swing in opposite directions, and are impulsed by two separate going trains. Breguet and Janvier both found that in such a clock, any rate error in one pendulum tended to be cancelled out by the other. Breguet’s notes, from an undated paper in which he describes his experiments, notes “This appears to be absurd, but experiment proves it a thousand times over.”

# Resonance in Timekeeping

Resonance pendulum clocks and watches are extremely rare – only three resonance watches were made by Breguet, and he and Janvier between them made only six resonance clocks (three each, with one by Breguet now lost) and the inventory of modern makers is quite short: Beat Haldimann, Buchanan, Gagneux, Frische and Schaeurte (while students at the watchmaking school in Bienne) and Walter. David Walter’s most recent double pendulum clock is a remarkable work greatly influenced by that of Breguet, with two separate trains showing solar and sidereal time, it’s described here (http://www.davidwalter.com/double-pendulum-clock/).

Resonance wristwatches are made by almost no one – other than FP Journe, the only modern maker we’re aware of is Beat Haldimann, who makes the H2 Resonance Flying Tourbillon.

In 2012, Christie’s auctioned a previously unknown Breguet resonance pocket watch – only the third known to exist; for many decades it was thought only two had been made by Breguet – and this watch is described by Aurel Bacs in this video:

Excerpted from an article by Jack Forster in REVOLUTION’s archives.