A Celebration of Watchmaking Ingenuity With Arnold & Son

When context is everything

While John Arnold was captivated by the understated design of Abraham-Louis Breguet’s watches and his understanding of complex kinematics, Abraham-Louis Breguet was fascinated by his English friend’s ability to invent simple mechanisms that could be mass-produced and approached a chronometric precision that no other watchmaker of the time could hope to achieve. During their exchanges, which included sending their respective sons to train with the other, these two geniuses were able to work out the best way of eliminating the running errors of watch balances.

The English watchmaker concentrated on optimising his detent escapement and developing balances, such as special springs, so as to offer instruments capable of satisfying his proto-industrial approach to chronometer construction – especially as the Admiralty asked him to produce them in ever greater quantities and at ever lower prices.

A chronometer designed to tell a story

As a tribute to their work and in memory of the friendship between these two watchmaking geniuses during the Age of Enlightenment, Arnold & Son has chosen to give this Constant Force Tourbillon 11 watch a 41.5 mm diameter 18-carat yellow gold case with a classic design. The yellow hue of this precious metal was chosen because it was often used by John Arnold for prestigious pocket watches at the time. It is in perfect harmony with the openworked bridge of the constant force mechanism, which is also made of 18-carat yellow gold. The timepiece’s curved case middle helps to reduce its profile. The front features a thin bezel set with a slightly domed sapphire crystal with an anti-reflective coating on both sides. On the reverse, it has an open case back in yellow gold with an identical sapphire crystal, revealing the manual winding manufacture calibre with the reference A&S5219. Water-resistant up to a pressure of 3 bar (30 metres or 100 feet), the watch is worn on an alligator leather strap fastened around the wrist with a classic pin buckle in 18-carat yellow gold bearing the Arnold & Son monogram.

A constant force mechanism

To guarantee the isochronism of the regulating group over 100 hours of operation, the movement’s designers incorporated a patented constant force mechanism between the going train and the tourbillon. Visible on the dial side, its purpose is to smooth out the energy delivered by the barrels so as to prevent excessive or insufficient torque from affecting the oscillations of the balance in the tourbillon carriage. This constant force mechanism is held in place by an 18-carat yellow gold bridge and rotates over the course of one minute. In the Constant Force Tourbillon 11, it replaces the fusee-and-chain configuration used by John Arnold in his chronometers. As well as supplying a constant force, the system chosen for this timepiece also allows for a ‘dead-beat seconds’ indication, in which the direct-drive hand does not advance seamlessly, but instead makes successive jumps of exactly one second – much like the direct-drive seconds of marine chronometers, which also made very similar jumps (detent chronometers generally beat every half-second). In the configuration chosen for the Constant Force Tourbillon 11 watch, the seconds are not indicated by a conventional hand, but instead by the tip of a flame-blued anchor used as a structural bridge for the constant force mechanism.

A calibre worthy of the master of chronometers

The A&S5219 movement was specially developed by the Manufacture’s engineers and watchmakers to the specifications of the Constant Force Tourbillon 11 watch. To remain as faithful to the original movement as possible, this calibre is hand-wound. But while inspired by the past, it remains thoroughly contemporary. It is equipped with two identical barrels mounted in series, giving a 100-hour power reserve. These barrels alternate in driving the mechanism, the second being activated when the torque of the first falls below optimum output