The Tourbillon: Anti-Gravity for Watch Movements

Do you know what time it is? Chances are good that you used a computer or a cell phone to answer that question. The time on your phone is about as accurate as chronometry gets these days. That’s because cell networks are timed from satellites, which are in turn timed from atomic clocks. And these days, it may be that atomic clocks are the only clocks that matter.

Before this modern era of quartz and atomic accuracy, though, timepieces were mechanical. Clocks were driven by heavy weights that made them impractical for travel. It wasn’t until the mainspring-driven movement came along that timekeeping could even begin to become portable.

But while the invention of the mainspring made portable timepieces possible, it hurt their accuracy. That’s because the driving force of a tightly wound spring isn’t constant like that of an inert, solid weight.  So pocket watches weren’t exactly an overnight success. Early pieces were largely ornamental, and only told the hour. Worst of all, they would slow down throughout the day as the mainspring unwound, becoming useless unless wound several times a day. The mainspring wasn’t the only problem plaguing pocket watches, but it was the among the most obvious.

Time is a Balancing Act

Cutaway illustration of a pocket watch. Image via Wikipedia

Pocket watch accuracy was greatly improved when the balance spring came along. The balance spring acts like a pendulum does in a weight-driven clock to keep the gears moving at a metered pace.  Working in concert with the escapement, the balance spring governs the release of energy stored in the mainspring to the time wheels. Before the balance spring, energy from the mainspring was controlled only by the escapement. Even with the addition of balance springs, there was still a lot of room for improvement.

By nature, pocket watches spent much of their time in one of two positions: either stored upright in a waistcoat pocket, or lying flat in the hand or on a table. A famous Swiss-French watchmaker named Abraham-Louis Breguet believed that gravity and positional stagnancy affected his watch movements by causing them to run at varying speeds. In the late 1700s, he devised a solution: a kind of anti-gravity chamber that he called a tourbillon, a French word meaning ‘whirlwind’.

Caged Gymnastics

A single-axis tourbillon in motion. This gif shows two seconds of real-time motion and two seconds sped up. GIF via davisryan8

A tourbillon is known in horology (that’s the art and science of measuring time) as a type of complication. This term refers to anything a watch can do in addition to keeping the hours, minutes, and seconds. The simplest type of complication is a date keeper. The tourbillon is among the most complicated complications ever invented.

Breguet’s idea was to constantly rotate the elements of the watch movement at a controlled rate. This way, the positional errors would average out over time, essentially decreasing gravity’s effect on accuracy of the movement. To do this, Breguet mounted all the parts of the movement – that’s the escapement, balance wheel, and balance spring – in a cage, and rotated the cage at a rate of one revolution per minute.

Breguet’s tourbillon rotated the watch movement along a single axis. Though the tourbillon is debated now as to whether it was ever really useful, a single axis was all he needed keep the movement in motion against gravity. In the 1970s, someone made the first dual-axis tourbillon. Nowadays, there are three and even four-axis tourbillons being made here and there as the horological fascination continues.

Conspicuous Consumption

The watch in the banner is the Jaeger-LeCoultre Master Grande Tradition Gyrotourbillon 3 Jubilee watch, and you can watch it in motion below. You can see the balance spring quickly inhaling and exhaling inside the cage. This watch has a flying spherical tourbillon that moves in three axes, much like a gyroscope.