Marine chronometers: the watchmaking that made finding longitude possible
For centuries, a navigator could determine latitude from observations of the Sun or the stars, but still could not tell with sufficient precision how far east or west the ship had travelled. Longitude required a second reference: time. The hour of a known meridian had to be carried on board and compared with local time obtained astronomically. The marine chronometer was born to fulfil that mission — and, for watchmaking, it represented one of the hardest technical problems ever set for a purely mechanical device.
This article approaches the subject mainly from the watchmaker's point of view: the evolution of escapements, the management of motive force, temperature compensation, the balance and balance spring, gimbal suspension, rate trials and the different forms the naval chronometer has taken. It ends with a technical reading of the GUB No. 7986 kept aboard the Portuguese sail training ship Sagres.
NOTE: A marine chronometer is not a chronograph. A chronograph measures independent intervals of time; a marine chronometer is a precision timekeeper, designed to preserve a time reference as regularly as possible for weeks or months, while exposed to temperature, humidity, vibration and the motion of the ship. It is at once a clock, a scientific instrument and a piece of navigational equipment.
1. Longitude: when four seconds can mean a nautical mile
The Earth turns through approximately 360 degrees in 24 hours. On average, therefore, a difference of one hour corresponds to 15 degrees of longitude, four minutes to one degree and four seconds of time to one minute of arc. At the equator, one minute of arc of longitude is roughly one nautical mile. This makes the severity of the problem immediately clear: a few seconds of accumulated error could turn into miles of uncertainty in position.
The chronometric method consists of comparing local time — obtained by astronomical observation — with the reference time kept by the chronometer. If local noon occurs when the chronometer shows, say, 14:00 at the reference meridian, the two-hour difference represents approximately 30 degrees of longitude. The real calculation requires astronomical and nautical corrections, but the principle is this: turning a difference in time into an angle.
At the beginning of the eighteenth century no clock was stable enough for this task on the open sea. A pendulum clock could be very accurate on land, but a pendulum reacts to the acceleration and tilt of a ship. A portable timepiece with a balance faced other problems: friction, mainsprings of uneven quality, temperature variations, changes in amplitude, escapement errors and differences in rate between positions. Longitude thus became a problem of astronomy applied to precision watchmaking.
Marine chronometer GUB No. 7986 aboard the sail training ship Sagres. Photograph by the author. © IPR
2. Before Harrison: Sully, Le Roy, Berthoud and a story more European than it seems
The popular narrative tends to turn John Harrison into a lone inventor who solved longitude single-handedly. Harrison was decisive, but the real chronology is far richer. From the late seventeenth century and throughout the eighteenth, English, French and Swiss watchmakers tried out solutions for keeping time at sea.
Some built machines that failed, others arrived at technically remarkable solutions that were hard to manufacture, and others produced ideas that would only later be absorbed into the classic chronometer.
The only image thought to show Sully, on the left Marine timekeeper by Henry Sully, Paris, 1724
Henry Sully (probably, on the left) and his chronometer, the Marine timekeeper by Henry Sully, Paris, 1724
Henry Sully, an Englishman settled in France, built sea clocks in the first decades of the eighteenth century and published important work on the subject. His instruments did not solve the problem for good, but they belong to the lineage that precedes Harrison. Royal Museums Greenwich itself places Sully among the first chapters in the evolution of marine timekeeping.
Portrait attributed to Pierre Le Roy (1717–1785)
Portrait attributed to Pierre Le Roy, a diagram of his detent escapement and a photograph of his chronometer
In France, Pierre Le Roy was a fundamental figure. Horological historians credit him with one of the first formulations of the detent escapement and, above all, with a very clear understanding that chronometric precision required separating functions: an oscillator as free as possible, a brief and controlled impulse, and compensation for the effects of temperature. Le Roy is a classic example of a name of enormous technical importance that remains far less known to the public than Harrison.
Ferdinand Berthoud
Portrait of Ferdinand Berthoud and photographs of his marine chronometer
Ferdinand Berthoud equally deserves a place in the front rank. He presented a design for a sea clock to the French Royal Academy of Sciences in 1760, produced several experimental instruments, followed the European debate about Harrison closely and, from 1768, saw his clocks No. 6 and No. 8 tested on a voyage of just over a year. In 1770 he received the title of Horloger-Mécanicien du Roi et de la Marine and an order for twenty longitude clocks. Berthoud was no late imitator: he was a systematic researcher who published on the theory, construction, testing and use of sea clocks.
The history of longitude is therefore an international one. The mechanical solution did not appear in an instant; it took shape through accumulated experience with escapements, compensation, springs, balances, materials, lubrication and testing methods. Harrison stands at the centre of the British narrative, but continental watchmaking developed solutions of great depth in parallel.
3. John Harrison: from H1 to H4 — four machines, four ways of thinking about the problem
Harrison began by tackling the problem as a maker of large clocks. H1, presented in 1735, is a monumental, almost architectural machine. Instead of a pendulum it uses two large interlinked balances, so that disturbances from the ship affect both in a compensating way. The whole adopts low-friction solutions and an obsessive concern with thermal stability and isochronism.
H2 refined some elements, but Harrison detected a fundamental problem in the behaviour of the system and decided not to submit it to the planned ocean trials.
H3 occupied Harrison for about nineteen years. It is technically fascinating because it contains ideas that go beyond navigation: bimetallic compensation elements and a roller-bearing system intended to reduce friction. Even so, the machine did not reach the constancy he wanted. The most important thing to understand is that the partial failure of H3 pushed Harrison in a different direction: instead of continuing to add sophistication to a large machine, he moved towards the architecture of the portable watch.
Around 1751–1753, John Jefferys built a watch to Harrison's specifications. The behaviour of that watch convinced Harrison that a relatively large balance, oscillating at high frequency and with a large amplitude, could resist the ship's disturbances better than the big systems of paired balances. From this came H4, begun in 1755 and completed in 1759.
H4 looks like an enormous pocket watch, but the resemblance is misleading. Its balance runs at five beats per second, very fast by the standards of the day, and with high energy. Harrison uses a deeply refined verge escapement, with diamond pallets, and a remontoire/constant-force system intended to isolate the regulator from variations in the transmission. Contrary to what many summaries suggest, H4 is not yet the classic detent chronometer that would dominate the nineteenth century; it is a very personal solution of Harrison's, enormously complex and hard to reproduce.
John Harrison, H4, 1759. Illustration based on a National Maritime Museum photograph. John Harrison, H4, 1759. Illustration based on a National Maritime Museum photograph. John Harrison, H4, 1759. Illustration based on a National Maritime Museum photograph.
John Harrison, H4, 1759. About 13 cm in diameter, with a high-frequency, large-amplitude balance, Harrison's fourth longitude timekeeper marked a radical change from the earlier large mechanisms. Illustration based on a photograph from the National Maritime Museum, Greenwich, inv. ZAA0037 (background altered).
The trial voyages of H4 proved that the mechanical route could work. The instrument met the most demanding limits set by the Longitude Act, although the award of the full prize was politically and institutionally troubled. Harrison was eventually rewarded by Parliament, but the real question left unresolved was another:
how to turn an almost unrepeatable masterpiece into an instrument that dozens or hundreds of ships could buy, maintain and use?
4. The next problem: working was not enough, it had to be manufacturable
Harrison demonstrated that it was possible. Larcum Kendall, John Arnold and Thomas Earnshaw helped to turn it into a reproducible technology. Kendall built K1 as a very faithful copy of H4. The instrument accompanied James Cook on his second voyage to the Pacific, between 1772 and 1775, and Cook recorded his approval of its accuracy. K1 was enormously important because it showed that the solution could leave Harrison's workshop and work in real service, even though the cost was still too high for general adoption.
John Arnold followed a different strategy: simplify. He developed lower-cost chronometers, worked intensively on compensation balances and helical balance springs, and improved the detent escapement. His No. 36, of 1778, is historically important and is associated with the consolidation of the term chronometer as applied to a portable precision timepiece. Arnold understood that the future lay not in copying H4 piece by piece, but in reducing the number of parts, making adjustment more rational and bringing production closer to a commercial scale.
Oil portrait of John Arnold with his family, painted by Robert Davy between 1783 and 1787 Marine chronometer by John Arnold & Son, London, c. 1795. Photo: Daderot / Wikimedia Commons, CC0
Left: John Arnold with his family, accompanied by his son John Roger Arnold and his wife, Margaret. Painting by Robert Davy, c. 1783–1787. Clockmakers’ Museum / Science Museum Group. Right: Marine chronometer by John Arnold & Son, London, c. 1795. Photograph: Daderot / Wikimedia Commons, CC0.
Thomas Earnshaw took that simplification further still. The priority dispute between Arnold and Earnshaw over the spring detent escapement has never entirely disappeared from the literature, but the practical consequence is unequivocal: the configuration associated with Earnshaw became the dominant standard for marine chronometers in the nineteenth and twentieth centuries. In 1804 the Board of Longitude went so far as to have models made of the systems of Earnshaw and John Roger Arnold in order to study the question. Both received rewards for their contribution to the advancement of marine timekeepers.
Thomas Earnshaw (1749–1829), portrait with a chronometer of the type he helped make standard Thomas Earnshaw (1749–1829), portrait with a chronometer of the type he helped make standard
Thomas Earnshaw (1749–1829). Portrait with a chronometer of the type he helped to establish as the standard of marine timekeeping. National Maritime Museum, Greenwich.
Thomas Mudge, Josiah Emery and other makers also developed chronometers and escapements of great interest. The actual history is less linear than a sequence ‘Harrison → modern chronometer’: several technical families competed, and the selection of the final standard resulted as much from performance as from cost, ease of adjustment, maintenance and production capacity.
5. Are there categories of marine chronometer? Yes — but no single universal classification
The word “chronometer” does not designate a specific physical form, but a timepiece designed and adjusted to achieve high precision and, above all, very stable running. In the maritime context, it is useful to separate several categories that overlap historically.
The first is the box chronometer: the classic instrument housed in a wooden box, with the movement in a metal container — the bowl — suspended in gimbals. This is the configuration we most readily associate with the marine chronometer today, and it is also the category to which the GUB of NRP Sagres belongs.
Second come pocket chronometers: high-precision pocket watches, sometimes fitted with a detent escapement and with chronometric solutions similar to those used in marine instruments. John Arnold played a particularly important part in developing this category. Not all of these watches served as the main reference on board, but they showed that the principles of precision timekeeping could be applied to much smaller, more portable instruments.
A third category of great practical importance is the deck watch. On many ships the main chronometer stayed protected in its place of installation, while a portable high-precision watch, previously compared or synchronised with it, was taken on deck during astronomical observations. This avoided moving the reference chronometer unnecessarily and reduced the risk of shock, change of position or disturbance to its rate.
Makers such as Ulysse Nardin, Longines, Hamilton and others produced high-quality deck watches for navies and hydrographic services.
Chronometers are also commonly classified by their duration — one-day, two-day, eight-day — although the name does not always correspond exactly to the total running time. Two-day chronometers became very common: a reserve of more than 48 hours allowed the instrument to be wound daily at the same hour, keeping it away from the extreme zones of the mainspring's force curve. There are also sidereal chronometers, intended to keep sidereal time for astronomical purposes, and observatory chronometers, whose classification derives mainly from their testing regime and scientific use.
Finally, we can distinguish mechanical, electromechanical and quartz chronometers. This technological classification becomes especially relevant in the twentieth century, when many navies kept mechanical chronometers for some time alongside electronic references before the final transition to quartz, radio and satellite.
6. The escapement: from Harrison to the detent
The escapement is the organ that turns the continuous energy of the going train into a sequence of impulses and, at the same time, allows the oscillator to set the pace of the timepiece. In a precision chronometer, the ideal is for the escapement to interfere with the balance as little as possible. The longer the balance is free, the less its period depends on the state of the power transmission, the lubrication or the geometry of the contact surfaces.
H4 is an important historical exception. Harrison used an extremely refined form of the verge escapement, normally regarded as archaic and with heavy recoil. With diamond pallets, a high frequency, carefully controlled amplitudes and a sophisticated constant-force system, he managed to draw extraordinary performance from this principle. This shows that in watchmaking it is not enough to identify the ‘type’ of escapement: the quality of the complete design and of the adjustment can change the result radically.
Marine chronometer in a wooden box, suspended in gimbals. On the right, a view of the movement inside the bowl, showing the precision mechanical architecture typical of these instruments.
The path that eventually won was the detent escapement. In the pivoted detent version, the detent turns on pivots. In the spring detent version, the elastic element itself replaces the pivots and reduces friction. The principle is that of a detached escapement: for almost the whole oscillation the balance is not in contact with the escapement. Only on one pass does the balance unlock the escape wheel and receive impulse; on the return swing the system lets it pass without a new impulse.
The advantages are enormous: little sliding friction, a brief impulse close to the tangent, little need for lubrication on the critical surfaces and freedom of the balance during most of the cycle. The drawback is delicacy. The detent escapement is sensitive to shocks, demands very fine tolerances and, in many configurations, is not self-starting. In an everyday pocket watch this would be a problem; in a protected chronometer, mounted in gimbals and handled by professionals, the trade-off made sense.
Chronometer by Thomas Earnshaw associated with HMS Beagle. The movement uses a fusee, Harrison's maintaining power, a spring-detent escapement, a compensated bimetallic balance and a free helical balance spring. Photograph: BabelStone / Wikimedia Commons, CC0.
7. Fusee, chain and maintaining power: how to deliver force without spoiling the rate
The mainspring does not deliver the same torque when fully wound as when it is nearing the end of its reserve. In an ordinary watch the escapement and regulator can tolerate part of this variation. In a marine chronometer, a change in the amplitude of the balance can cause a change in rate and, therefore, an error in longitude. The fusee and chain is an elegant mechanical solution for evening out the delivery of force.
The spring drives a chain — or, in some chronometers, a flexible metal band — wound between the barrel and a conical part called the fusee. When the spring is strong, the chain acts on a zone of small radius; as the spring weakens, it moves to a zone with a longer lever arm. The profile of the fusee is calculated to compensate for the torque curve of the spring. The ideal result is a much more constant force applied to the train.
Another problem then arises: during winding, if the transmission is interrupted, the chronometer momentarily stops receiving energy. Harrison therefore developed a device for maintaining power during winding, which keeps the train driven at least while the mainspring is being wound. This mechanism became a classic feature of many high-quality chronometers and shows clearly how every operation liable to disturb the rate was treated as a potential source of chronometric error.
Regular winding was equally important. It was customary to wind the chronometer at about the same time every day, keeping it within a more predictable working zone and avoiding unnecessary variations in the tension of the mainspring. The state-of-wind indicator — Up/Down or Auf/Ab — was therefore not a decorative complication but a functional element for controlling the instrument.
8. Balance and balance spring: where precision is won or lost
The regulating organ is the true clock within the clock. The balance oscillates; the escapement turns those oscillations into the regular advance of the train. In a classic chronometer the aim is a large balance, with high inertia, carefully poised and paired with a balance spring that develops as concentrically as possible. The helical balance spring, cylindrical in form, became a frequent solution because it allows a more symmetrical expansion and contraction than many flat springs of the period.
Many chronometers use a free-sprung balance, with no conventional index to alter the active length of the spring. Regulation is done through the inertia of the balance, by means of weights or compensation screws. This removes a point of disturbance on the spring and makes the system potentially more stable. Fine adjustment, however, demands enormous skill.
Temperature was for a long time the great enemy. The elastic modulus of the steel balance spring varies with temperature; at the same time, the components of the balance expand. The cut bimetallic balance exploits the difference in expansion between two metals: as the temperature rises, the arms curl and move mass closer to the axis, compensating for the spring's tendency to make the timepiece lose. Screws distributed around the rim let the watchmaker adjust the compensation carefully.
Even this solution is not perfect. A bimetallic balance can be correctly compensated at the extremes of a temperature range and still show an error at intermediate temperatures — the so-called middle-temperature error. In the nineteenth century auxiliary compensation systems appeared and, later, special alloys such as the Guillaume balance and balance springs of low thermal sensitivity.
The history of the chronometer is, to a large extent, the history of a successive struggle against ever smaller errors.
9. Isochronism, amplitude, poising and positional errors
An ideal regulator would have the same period regardless of amplitude. In reality, changes in amplitude alter the rate slightly. The aim of isochronism is to reduce that dependence. The design of the balance spring, the shape of the terminal curves, the relationship between balance and spring, the constancy of the force and the escapement all play a part in the result. That is why chronometry cannot be understood by looking at a single component in isolation.
Poising — the static and, ideally, dynamic balance of the balance wheel — is equally critical. If the centre of mass does not coincide with the axis, gravity introduces position-dependent errors. In a box chronometer, the gimbal suspension reduces the variety of positions of the movement, keeping it roughly horizontal, but it does not remove the need for precise poise. Deck watches and pocket chronometers, on the other hand, are adjusted for multiple positions because they spend far more time vertical or tilted.
Endshake, pivot geometry, the quality of the jewels and the viscosity of the lubricants also alter amplitude and rate. The chronometer is a system in which micrometres of difference, small contaminations or aged oil can become seconds per day. That is why maintaining a chronometer requires precision watchmaking methods and not merely ‘cleaning and oiling’.
10. Adjustment and trials: the value lies in a known rate, not in showing the exact time today
An essential principle of naval chronometry is often misunderstood: it is not indispensable for the chronometer to show exactly the right time at every moment; what is indispensable is to know its error and, above all, for its rate to be regular. If a chronometer gains 0.8 seconds a day in an extremely constant way, that deviation can be applied mathematically. A timepiece that is right today, loses three seconds tomorrow and gains two the day after is far less useful.
Observatories and hydrographic services developed systematic trials: rate at different temperatures, changes of position, variations in amplitude and prolonged periods of observation. The competitions and tests of the nineteenth and twentieth centuries were not mere commercial displays; they worked as laboratories in which the stability of an instrument was assessed under standardised conditions.
A chronometer's record sheet could log the difference from the standard every day. From that series the mean rate was obtained and variations were observed. For navigation, the officer applied the known error of the instrument to the time indicated.
This culture of measurement — measuring the error of the measuring device itself — is one of the most important ideas inherited from marine chronometry.
11. Gimbals and box: part of the mechanism, not mere furniture
The metal container that holds the movement is mounted in two rings with perpendicular axes — the gimbal suspension. When the ship rolls or pitches, gravity tends to keep the inner assembly roughly horizontal. This reduces positional errors and protects the geometric relationship between escapement and regulator. That is why the suspension must be understood as a functional part of the chronometric instrument.
The wooden box also has precise functions: to cushion shocks, keep out dust, protect the glass and the suspension and allow safe transport. Many have two-tier lids, viewing windows, a place for the key and plates with instructions. Some models include devices for locking the gimbals during transport. Carrying a chronometer unlocked, or setting it down without regard for the suspension, can produce stresses the system was not designed for.
The Sagres chronometer in its box. The gimbal suspension, the transport box and the configuration of a naval instrument are visible. Photograph by the author.
12. How a chronometer was used on board
Before departure, the chronometer was compared with a known time reference.
On board, it was kept running continuously and its hands were not normally touched every day to ‘set’ it. The error and the rate were recorded. When Greenwich time — or that of another reference meridian — was needed, the calculated correction was applied to what the instrument showed.
Determining longitude by chronometer also involved a sextant, observations of the Sun or stars, nautical almanacs and calculation. The chronometer did not ‘tell the position’; it supplied the indispensable time variable. The quality of the whole process depended as much on watchmaking as on the observation and mathematical discipline of the navigator.
Important ships often carried several chronometers. Comparing them made it possible to detect an abnormal change of rate in one instrument. Redundancy was essential because, on the ocean, a failure could not be solved by simply sending the device to the workshop. The deck watch, where there was one, was synchronised with the main chronometer and used to carry the time to the place of observation without moving the master instrument.
From the nineteenth century onwards, visual time signals in ports — such as time balls — and later the telegraph and radio made comparison and correction easier. Even so, the chronometer remained important as an autonomous reserve and as the link between astronomical observation and standard time.
13. Glashütte: when German chronometry goes to sea
During the nineteenth century Glashütte became a centre of precision watchmaking and began producing marine chronometers in 1886. The German tradition developed instruments for navies, observatories and merchant shipping, combining the international architecture of the classic chronometer with its own standards of production and testing.
After the Second World War, the Glashütte industry, located in East Germany, was reorganised. In 1951 several companies were merged into VEB Glashütter Uhrenbetriebe, GUB. Production of mechanical marine chronometers continued for decades. The Deutsches Uhrenmuseum Glashütte documents, for example, chronometer GUB No. 8888 as made in 1965 and states that the factory kept producing mechanical chronometers until 1978, alongside quartz chronometers from 1974.
GUB chronometers belong fully to the box-chronometer tradition: a large movement, a chronometer escapement, a compensated balance, a balance spring suited to chronometric service, seconds and state-of-wind indication, and gimbal suspension. The Glashütte school valued functional finishing and precision; in these instruments, decoration is secondary to stability and ease of maintenance.
14. The GUB No. 7986 of the sail training ship Sagres
In the photographs taken aboard the sail training ship Sagres one can clearly identify a GUB chronometer — Glashütter Uhrenbetriebe — with the number 7986 on the dial. The layout is classic: central hours and minutes, small seconds at 6 o'clock, Roman numerals and a power-reserve indicator at 12 o'clock. The inscriptions ‘AUF’ and ‘AB’ are the German indication of the state of wind.
Marine chronometer GUB No. 7986 of NRP Sagres, mounted in gimbals inside its wooden box. The main dial, the small seconds and the Auf/Ab state-of-wind indicator are visible. Photograph: IPR. © IPR
The assembly is mounted in a metal bowl suspended in gimbals inside a wooden box. Reading from above and the high legibility of the dial were designed for instrument service. By comparison with documented GUB numbers, No. 7986 plausibly places this example in the early 1960s. The German museum itself says it holds the commercial records of GUB chronometers and can provide archive information.
It is equally important not to extrapolate too much from the dial. To document this example technically and definitively, the instrument would have to be opened under controlled conditions and the movement photographed: escapement, balance, balance spring, fusée, train, maker's marks, internal numbers and any signs of repair. In an instrument that served for decades, parts may have been replaced and adjustments may not correspond exactly to the factory state.
The value of No. 7986 is twofold. It is a physical example of twentieth-century Glashütte chronometry and, at the same time, an object set within one of the great symbols of the Portuguese Navy. On a training ship the chronometer also has teaching value: it makes tangible the relationship between watchmaking, astronomy, navigation and shipboard discipline.
15. From the mechanical chronometer to quartz, radio and GPS
The twentieth century gradually changed the operational role of the mechanical chronometer. First, radio time signals made it possible to compare shipboard time with external standards without entering port. Then quartz oscillators offered far greater stability with much less maintenance. GUB is a good example of the transition: mechanical chronometers continued to be made until 1978, while quartz production began in 1974.
Satellite navigation systems eventually transformed the problem completely. GPS provides position and an extremely precise time reference at the same time. What for two centuries required a chronometer, sextant, almanac and calculation can now be obtained electronically in seconds. But this does not make the chronometer historically irrelevant; it makes what watchmakers achieved with nothing but springs, wheels, pivots, jewels, compensating metals and a mechanical oscillator all the more remarkable.
There is also a contemporary lesson about redundancy. Modern navigation depends on extraordinarily effective electronic systems, but maritime training continues to value independent methods. To know celestial navigation and to understand the marine chronometer is to understand how to build a chain of position-fixing that does not depend on a single technology.
16. Conservation and restoration: a historic chronometer is not just a clock to be set going
Conserving a historic chronometer calls for a different approach from repairing an everyday watch. The aim should not automatically be to achieve the best possible rate at the cost of replacing original components. Functional intervention must be distinguished from heritage preservation. A spring, a chain, a pivot, a detent or a balance spring can hold historical information as important as the dial.
Before dismantling, there should be complete photographic documentation. Watchmakers' marks, service scratches, serial numbers, plugged holes, non-original screws and any evidence of earlier interventions should be recorded. In chronometers that served in navies, these alterations can tell the operational history of the instrument. ‘Correcting’ them without documentation can erase information irreversibly.
Lubrication deserves particular care. Some chronometer escapements were designed precisely to work without oil on the critical surfaces. Applying lubricant where the design does not call for it can degrade the rate and create adhesion. Likewise, the adjustment of the detent, the depth of locking, the passage of the unlocking jewel and the relationship of the impulse pallet must be carried out by someone familiar with chronometer escapements, not just with the Swiss lever.
17. Why the marine chronometer is one of the great machines in the history of watchmaking
The marine chronometer forced watchmakers to turn abstract concepts — isochronism, elasticity, thermal expansion, friction, torque — into hand-worked metal. The result was not just a more accurate timepiece. It was a technology that changed navigation, cartography, trade, scientific exploration and naval power. Few fields show so directly the passage of watchmaking from mechanical art to precision science.
Harrison proved it was possible. Le Roy and Berthoud developed their own solutions and a rigorous theory. Kendall demonstrated viability in service. Arnold simplified and miniaturised. Earnshaw helped to establish the architecture that would dominate production for more than a century. Then came British, Swiss, American, German and other makers, taking the chronometer to an almost industrial maturity without abandoning the craft demands of fine adjustment.
The GUB No. 7986 of the sail training ship Sagres is a late piece of that long tradition. Its dial, gimbal suspension, power reserve and wooden-box assembly are the visible result of more than two hundred years of attempts to do something apparently simple: carry the right time across the ocean.
Bibliography and reference sources
Royal Museums Greenwich — collections and documentation on the H1, H2, H3 and H4 timekeepers, the history of the longitude problem, John Harrison, John Arnold, Thomas Earnshaw, Larcum Kendall's K1 and the chronometer records of the Royal Observatory, Greenwich.
German Watch Museum Glashütte (Deutsches Uhrenmuseum Glashütte) — collection of marine chronometers and historical documentation on the development, production and marketing of these instruments in Glashütte, including those made by VEB Glashütter Uhrenbetriebe (GUB).
Ferdinand Berthoud — historical documentation on sea clocks Nos. 1, 6 and 8, the French naval trials, Ferdinand Berthoud's publications and his work as Horloger-Mécanicien du Roi et de la Marine.
Jonathan Betts, Marine Chronometers at Greenwich: A Complete History of the Marine Timekeepers at the Royal Observatory from John Harrison to the Present Day.
Jonathan Betts, John Harrison and the Quest for Longitude.
Rupert T. Gould, The Marine Chronometer: Its History and Development.
Hans von Bertele, Marine- und Taschenchronometer.
Comments