A chronometer (Ancient Greek: , khronmetron, "time measurer") is an extraordinarily accurate mechanical timepiece, with an original focus on the needs of maritime navigation. In Switzerland, timepieces certified by the Contrle Officiel Suisse des Chronomtres (COSC) may be marked as Certified Chronometer or Officially Certified Chronometer. Outside Switzerland, equivalent bodies, such as the Japan Chronometer Inspection Institute, have in the past certified timepieces to similar standards, although use of the term has not always been strictly controlled.
The term chronometer was coined by Jeremy Thacker of Beverley, England in 1714, referring to his invention of a clock ensconced in a vacuum chamber.The term chronometer is also used to describe a marine chronometer used for celestial navigation and determination of longitude. The marine chronometer was invented by John Harrison in 1730. This was the first of a series of chronometers that enabled accurate marine navigation. From then on, an accurate chronometer was essential to open-ocean marine or air navigation out of sight of land. Early in the 20th century the advent of radiotelegraphy time signals supplemented the onboard marine chronometer for marine and air navigation, and various radio navigation systems were invented, developed, and implemented during and following the Second World War (e.g., Gee, Sonne (a.k.a. Consol), LORAN(-A and -C), Decca Navigator System and Omega Navigation System) that significantly reduced the need for positioning using an onboard marine chronometer. These culminated in the development and implementation of global satellite navigation systems (GSN-GPS) in the last quarter of the 20th century. The marine chronometer is no longer used as the primary means for navigation at sea, although it is still required as a backup, since radio systems and their associated electronics can fail for a variety of reasons.
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Once mechanical timepiece movements developed sufficient precision to allow for accurate marine navigation, there eventually developed what became known as "chronometer competitions" at astronomical observatories located in Europe. The Neuchtel Observatory, Geneva Observatory, Besancon Observatory, and Kew Observatory are prominent examples of observatories that certified the accuracy of mechanical timepieces. The observatory testing regime typically lasted for 30 to 50 days and contained accuracy standards that were far more stringent and difficult than modern standards such as those set by COSC. When a movement passed the observatory, it became certified as an observatory chronometer and received a Bulletin de Marche from the Observatory, stipulating the performance of the movement. Because only very few movements were ever given the attention and manufacturing level necessary to pass the Observatory standards, there are very few observatory chronometers in existence.
Most observatory chronometers had movements so specialized to accuracy that they could never withstand being used as wristwatches in normal usage. They were useful only for accuracy competitions, and so never were sold to the public for usage. However, in 1966 and 1967, Girard Perregaux manufactured approximately 670 wristwatches with the Calibre 32A movement, which became Observatory Chronometers certified by the Neuchatel Observatory, while in 1968, 1969 and 1970 Seiko had 226 wristwatches with its 4520 and 4580 Calibres certified. These observatory chronometers were then sold to the public for normal usage as wristwatches, and some examples may still be found today.
The observatory competitions ended with the advent of the quartz watch movement, in the late 1960s and early 1970s, which generally has superior accuracy at far lesser costs. In 2009, the Watch Museum of Le Locle renewed the tradition and launched a new chronometry contest based on ISO 3159 certification. In 2017 the Observatory Chronometer Database (OCD) [1] went online, which contains all mechanical timepieces ("chronometres-mecaniques") certified as observatory chronometers by the observatory in Neuchatel from 1945 to 1967, due to a successful participation in the competition which resulted in the issuance of a Bulletin de Marche. All database entries are submissions to the wristwatch category ("chronometres-bracelet") at the observatory competition.
The term chronometer is often wrongly used by the general public to refer to timekeeping instruments fitted with an additional mechanism that may be set in motion by pushbuttons to enable measurement of the duration of an event. Such an instrument, typically called a stopwatch, is in fact a chronograph or chronoscope. It may be chronometer certified, provided it meets the criteria set for the standard.
A mechanical chronometer is a spring-driven escapement timekeeper, like a watch, but its parts are more massively built. Changes in the elasticity of the balance spring caused by variations in temperature are compensated for by devices built into it.[2]
Chronometers often included other innovations to increase their efficiency and precision. Hard stones such as diamond, ruby, and sapphire were often used as jewel bearings to decrease friction and wear of the pivots and escapement. Chronometer makers also took advantage of the physical properties of rare metals such as gold, platinum, and palladium.
Quartz and atomic timepieces have made mechanical chronometers obsolete for time standards used scientifically and/or industrially. Most watchmakers do still produce them. However, they are mostly considered status symbols promoted by luxury watchmakers as a symbol of fine craftmanship and aesthetics.
A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. It is used to determine longitude by comparing Greenwich Mean Time (GMT), and the time at the current location found from observations of celestial bodies. When first developed in the 18th century, it was a major technical achievement, as accurate knowledge of the time over a long sea voyage was vital for effective navigation, lacking electronic or communications aids. The first true chronometer was the life work of one man, John Harrison, spanning 31 years of persistent experimentation and testing that revolutionized naval (and later aerial) navigation.
The term chronometer was coined from the Greek words (chronos) (meaning time) and meter (meaning measure). The 1713 book Physico-Theology by the English cleric and scientist William Derham includes one of the earliest theoretical descriptions of a marine chronometer.[1] It has recently become more commonly used to describe watches tested and certified to meet certain precision standards.
To determine a position on the Earth's surface, it is necessary and sufficient to know the latitude, longitude, and altitude. Altitude considerations can naturally be ignored for vessels operating at sea level. Until the mid-1750s, accurate navigation at sea out of sight of land was an unsolved problem due to the difficulty in calculating longitude. Navigators could determine their latitude by measuring the sun's angle at noon (i.e., when it reached its highest point in the sky, or culmination) or, in the Northern Hemisphere, by measuring the angle of Polaris (the North Star) from the horizon (usually during twilight). To find their longitude, however, they needed a time standard that would work aboard a ship. Observation of regular celestial motions, such as Galileo's method based on observing Jupiter's natural satellites, was usually not possible at sea due to the ship's motion. The lunar distances method, initially proposed by Johannes Werner in 1514, was developed in parallel with the marine chronometer. The Dutch scientist Gemma Frisius was the first to propose the use of a chronometer to determine longitude in 1530.
The creation of a timepiece which would work reliably at sea was difficult. Until the 20th century, the best timekeepers were pendulum clocks, but both the rolling of a ship at sea and the up to 0.2% variations in the gravity of Earth made a simple gravity-based pendulum useless both in theory and in practice.
Christiaan Huygens, following his invention of the pendulum clock in 1656, made the first attempt at a marine chronometer in 1673 in France, under the sponsorship of Jean-Baptiste Colbert.[5][6] In 1675, Huygens, who was receiving a pension from Louis XIV, invented a chronometer that employed a balance wheel and a spiral spring for regulation, instead of a pendulum, opening the way to marine chronometers and modern pocket watches and wristwatches. He obtained a patent for his invention from Colbert, but his clock remained imprecise at sea.[7] Huygens' attempt in 1675 to obtain an English patent from Charles II stimulated Robert Hooke, who claimed to have conceived of a spring-driven clock years earlier, to attempt to produce one and patent it. During 1675 Huygens and Hooke each delivered two such devices to Charles, but none worked well and neither Huygens nor Hooke received an English patent. It was during this work that Hooke formulated Hooke's law.[8]
The first published use of the term chronometer was in 1684 in Arcanum Navarchicum, a theoretical work by Kiel professor Matthias Wasmuth. This was followed by a further theoretical description of a chronometer in works published by English scientist William Derham in 1713. Derham's principal work, Physico-theology, or a demonstration of the being and attributes of God from his works of creation, also proposed the use of vacuum sealing to ensure greater accuracy in the operation of clocks.[9] Attempts to construct a working marine chronometer were begun by Jeremy Thacker in England in 1714, and by Henry Sully in France two years later. Sully published his work in 1726 with Une Horloge invente et execute par M. Sulli, but neither his nor Thacker's models were able to resist the rolling of the seas and keep precise time while in shipboard conditions.[10] 152ee80cbc
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