Constant Force Tourbillon 11

A celebration of watchmaking ingenuity

The 41.5 mm diameter Constant Force Tourbillon 11 watch in 18-carat yellow gold, released by Arnold & Son as a limited edition of 11, is driven by a hand-wound mechanical movement. Equipped with two barrels to give a 100-hour power reserve, this timepiece was entirely developed and built at the manufacture in La Chaux-de-Fonds. It is fitted with a constant force mechanism visible on the enamel dial and is regulated by a tourbillon that can be seen on the back. The architecture of this calibre is inspired by that of the timekeeping instrument driven by the first tourbillon created by Abraham-Louis Breguet in 1808, based on a chronometer movement designed by John Arnold. This first tourbillon regulator, now in the British Museum, was given to John Roger Arnold by the Paris-based watchmaker in honour of his scientific collaboration and friendship with his father. The Constant Force Tourbillon 11 timepiece, designed to mark the end of the 260th anniversary celebrations of John Arnold’s legacy, pays tribute to the watchmaker’s ingenuity and his close association with Abraham-Louis Breguet. 

The greatest watchmakers of the Age of Enlightenment often knew each other. Some of them exchanged views and appreciated each other despite language barriers and political obstacles. And this was the case with John Arnold and Abraham-Louis Breguet. These two watchmakers, undoubtedly the most productive of the second half of the 18th century, forged a friendship that nothing could shake, not even the throes of war between the two countries or the French Revolution. Aware of their respective talents, during Abraham-Louis Breguet’s frequent trips to London between 1789 and 1791, they shared their views and knowledge of the principles of timekeeping, furthering the science of timekeeping, which in their eyes definitely knew no frontiers. 

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.  

Meanwhile, Abraham-Louis Breguet, inspired by his conversations with his English friend on the principles of high chronometry, continued to work on developing the tourbillon during his exile in Switzerland from 1792. On his return to Paris in 1795, he wrote about the development of a rotating carriage in a letter. Then, two years after John Arnold’s death in 1799, he patented this mechanism under the name ‘tourbillon’ in Paris on 26 June 1801, i.e. 7 Messidor Year IX according to the French Republican calendar still in effect at the time.  

To honour the memory of his friend and remember the research they had carried out together, he based his first tourbillon regulator on the movement of John Arnold’s marine chronometer no. 11. He screwed an engraved silver plate onto the main bridge with the following dedication: “The first tourbillon regulator by Breguet incorporated in one of the first works of Arnold. Breguet's homage to the revered memory of Arnold. Presented to his son in the year 1808.” This timekeeping instrument, now in the British Museum, was given to John Roger Arnold, who succeeded his father as head of the workshop and London boutique.  

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 precious and captivating dial

For the Constant Force Tourbillon 11 timepiece, Arnold & Son chose a white Grand Feu enamel dial to recall the dials of the ship’s chronometers that John Arnold offered to English naval officers in his London boutique. This disc was individually produced by a specialist artisan on an 18-carat yellow gold base. White enamel is obtained by melting powdered materials in a kiln heated to just over 800°C. After firing the enamel several times to achieve the required thickness, the surface is lapped to make it smooth and even. Then, as long as the material has not cracked and there are no imperfections that would spoil the white colour, a translucent enamel is applied and the disc is fired one last time. This gives it depth and transparency, bringing out the full magic of the enamel, whose hue is permanent and is called ‘Grand Feu’ (great fire) because it is vitrified by melting. Openings are then made in this delicate and precious disc to accommodate the constant force mechanism and white opal subdial – a true signature of the House. Here, for the first time at Arnold & Son, this fine stone has been recessed to give it a stronger visual presence and an angle that enhances the readability of the black transfer Roman numerals. 

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. 

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 system intended to smooth out positional errors

Designed to celebrate the friendship between John Arnold and Abraham-Louis Breguet, the Constant Force Tourbillon 11 watch has a transparent anti-reflective sapphire crystal case back that showcases the architecture of the A&S5219 calibre, inspired by the back of the timekeeper kept in the British Museum. Here, the tourbillon carriage, which rotates once every minute, keeps the general design of the carriage used by John Arnold’s brilliant friend in the timepiece intended to commemorate their unbreakable friendship and embody the true scope of their joint research. The extremely refined tourbillon features a very thin, polished and rounded-off linear carriage bridge that reveals a variable inertia balance with inertia blocks inspired by the most sophisticated oscillators used in John Arnold’s chronometers. The House also chose to incorporate a T-shaped retaining spring inspired by the one used in the ‘pare-chute’ shock protection system developed by Abraham-Louis Breguet and which can be found on the tourbillon bridge of the original instrument. However, a Swiss lever escapement, which is more practical and less sensitive to shocks, was chosen over the detent escapement of the original timepiece.  

The finishes of the mainplate, bridge and tourbillon cock are virtually identical on both timepieces, while the grained and chamfered barrel bridge of the Constant Force Tourbillon 11 watch features hand-engraved inscriptions and the famous plate, which has a new text inspired by the original: “To the revered memory of John Arnold and Abraham-Louis Breguet. Friends in their time, legendary watchmakers always.” . These words underscore the historical and horological context of this Arnold & Son edition of 11 timepieces, where friendship and the art of timekeeping were the strongest driving forces.

Technical specifications

Functions

• hours, minutes, true-beat seconds

Movement

• Calibre: A&S5219 hand-wound mechanical movement, constant force, one-minute tourbillon
  
• Jewels: 35
  
• Diameter: 33 mm
  
• Thickness: 10.48 mm
  
• Power reserve: 100 hours
  
• Frequency: 3 Hz / 21,600 vph
• Finishes:
  mainplate: 3N golden finish, grained, polished angles
  barrel bridge: 3N golden finish, grained, polished angles, stretched edges, hand-engraved
  tourbillon bridge: golden finish, grained, polished angles, stretched edges, satin-finished Durnico steel retaining spring 
  screws: blued, chamfered, mirror-polished heads               
  tourbillon: mirror-polished carriage plate, satin-finished pallet bridge, mirror-polished stud-holder, rhodium-finished balance, polished and rounded-off carriage bridge
  constant force bridge: 18-carat yellow gold (3N), polished bevel, satin-finished flat surface, polished angles 
  constant force carriage lower bridge: flame-blued, mirror-polished, polished angles                 
  

Engraved plate

• To the revered memory of John Arnold and Abraham-Louis Breguet. Friends in their time, legendary watchmakers always.

Dial

• white Grand Feu enamel, 18-carat yellow gold (3N) base

Hour dial

• white opal, concave

Case

• Material: 18-carat yellow gold (3N)
  
• Diameter: 41.50 mm
  
• Depth: 13.70 mm
• Crystal: Domed sapphire with an anti-reflective coating on both sides
  
• Back: Sapphire crystal, anti-reflective coating on both sides
  
• Water-resistance: 30 metres / 3 ATM
  

Strap

• Material: midnight blue alligator leather with black alligator leather lining
  
• Buckle: pin buckle, 18-carat yellow gold (3N)

Reference                           

• 1FCBJ.E01A.C246J

Limited edition                    

• 11 pieces    

Astronomy, Chronometry and World Time

Arnold & Son's three founding principles

Throughout human history, measuring time has always referred to the stars. It was by observing certain stars and understanding their cycle that the first calendars were established with impressive accuracy. It took several millennia before this precision was enclosed in a timepiece like the ones designed by John Arnold. 

The golden age of maritime explorations and discoveries ushered this precision into a new technical ideal – determining longitude at sea. Its immediate corollary was the identification of local time, which changed constantly as the observer moved along an east-west axis. Astronomy, chronometry and what we now call world time are thus inextricably linked within one and the same question, to which John Arnold and his son devoted their lives, their art and their genius. 

This is how these three dimensions – astronomy, chronometry and world time – have come to be embodied in the House's contemporary timepieces.  Echoes of John Arnold's inventions and preoccupations, these pillars represent the foundations on which the Arnold & Son collections are based.

Chronometry: Be accurate

Rate accuracy, which is known as chronometry, is the key requirement of Arnold & Son's contemporary watchmaking. It is the standard of excellence for its collections, the first condition to be met and constantly checked, whether it is at the forefront or in the background of a watch designed by Arnold & Son. It is the most discreet of a movement's characteristics. 

When building an Arnold & Son collection, all the thinking is focused on this chronometry. The manufacture calibres are based on advanced technical fundamentals that are not necessarily the best known. One of them is the choice of small, lightweight balances capable of rapidly returning to their isochronous rate after the latter has been disturbed by inevitable everyday shocks. Another is the routine use of large barrels or even two series-coupled barrels to store the energy required for the movement to function.  They consequently provide Arnold & Son's manual winding calibres with above-average power reserves of 90 hours and more. A third is the particular attention paid to manufacturing the gear trains, roller-burnishing the pinions and polishing the gear teeth, as well as the precision of the machining and therefore the relative positions of the moving parts, a key concept in rate accuracy.

The tourbillon (or the fact of putting the regulating organ in rotation on its axis to best adjust the effects of gravity on the balance and its hairspring) was patented after John Arnold's death, but it was undoubtedly at the heart of his chronometric research and discussions with his friend Abraham-Louis Breguet, who incidentally assembled his first tourbillon on a John Arnold pocket watch in homage to this great watchmaker. Nowadays, the tourbillon has become a must in Arnold & Son collections.

While the tourbillon was not a complication in John Arnold's time, constant force underpinned the design of his marine chronometers. The regularity of the rate of the sprung balance relies on the consistency of the energy that it receives. However, this naturally fluctuates due to the circular and spiral nature of the mainspring contained in the barrel. To achieve a perfectly smooth torque, in other words a constant force, Arnold & Son uses a one-second constant-force mechanism. Housed just before the escapement, it stores up a small but always equal amount of energy in a secondary spring, the remontoire. Thus, every second, the sprung balance receives very precisely the same force to power its oscillations. These become more even, thereby creating the conditions for a high-precision rate.

Arnold & Son also works with another of John Arnold's historical chronometry indicators: deadbeat seconds, a mechanism that was indispensable to navigators at the time for calculating longitude. This mechanism advances one step each second, rather than six or eight smaller jumps in sync with the frequency of the balance. Instead of the term deadbeat seconds, Arnold & Son prefers a name whose very sound means accuracy: “true beat second”. Its jump is a signature of John Arnold's marine chronometers and a complication that is still alive and well in the House's collections.

Astronomy: Under the sky

The Pole Star, Southern Cross, astrolabes and sextant: measuring time has relied on the recurrence of astronomical phenomena in order to find long, reliable points of reference there that can be used under any conditions. The fruit of the human ingenuity, patience and dedication of countless observers and astronomers from every culture, these markers of cyclical time are foundational for Arnold & Son watchmaking.

Astronomical complications are a signature of Arnold & Son collections, with the moon as the heavenly body of choice, main subject and major inspiration. The distinctive feature of the Brand's moon phase timepieces is that they feature “astronomical” display precision as a matter of course. This term corresponds to an accumulated one-day deviation in the moon phase display every 122 years. Since setting this complication requires great finesse, the Arnold & Son moons generally have a double display with a secondary indicator on the case back next to the movement. This extremely rare display bears witness to Arnold & Son's involvement in all types of development and reflects its favoured themes, which are as much chronometric as astronomical.

Over and above their precision, Arnold & Son's moon phases attract all the light, either with a large moon opening up over half the dial, or with a 12-mm three-dimensional rotating moon, making it the largest of all moons. Whether in two or three dimensions, the moon is always treated as a small work of artistic craftsmanship, composed of materials that are rare in watchmaking such as marble or Paraíba tourmaline, or delicate such as mother-of-pearl, meteorite or aventurine glass. The Arnold & Son moon also shines at night, often with a subtle addition of luminescent material. 

World Time: Here, elsewhere, everywhere

With ocean navigation, humankind divided up the world and invented longitudes, which were calculated by comparing the local time, observed using the sun, and the time at a starting point, kept by an extremely reliable timepiece. John Arnold was one of the leading suppliers of chronometers to the British Navy. He was the one who successfully improved the reliability and simplified the production of these indispensable marine chronometers, so much so that he became a benchmark among great explorers such as James Cook and later Dr David Livingstone. The indication of several time zones is therefore integral to Arnold & Son's watchmaking identity.

As this navigation was itself inseparable from cartography, for this world time complication Arnold & Son has chosen to depict a three-dimensional terrestrial hemisphere, making it possible to tell what time it is at any point.

In parallel to this graphic vision, Arnold & Son has developed a second approach to the time elsewhere in the world: with a double tourbillon featuring two distinct rotating regulating organs, making it possible to follow time zones offset by 15, 30 or 45 minutes compared to a full hour – a freedom in terms of setting that remains extremely rare. 

Once again, and because this double display is based on a profoundly chronometric complication, Arnold & Son’s fundamental principles are interwoven. One never advances alone; there are always two – if not three – together. This is how a pillar's strength is measured: it relies on the next one, creating the conditions for a solidity that stands the test of time.