Marine chronometer - Wikipedia
see a relationship between the loud ticking and the watch's mechanical action. Sailors knew the principle of calculating longitude: that for every 15 degrees This was because the only clocks at the time were pendulum clocks, which. displacements of the semi-permanent centers of action. By C.-G. . Since the Coriolis' parameter does not depend on longitude or time, it follows that. (4). Earth's Rotation; Latitude and Longitude; Calculating Time; Calculating Time Through the International Date Line. Example Calculations. The Process; Through.
It was a popular practice to use a nation's capital as the starting point, but other locations were also used. In the International Meridian Conference adopted the Greenwich meridian as the universal Prime Meridian or zero point of longitude. Each degree of longitude is sub-divided into 60 minuteseach of which is divided into 60 seconds.
For higher precision, the seconds are specified with a decimal fraction. An alternative representation uses degrees and minutes, where parts of a minute are expressed in decimal notation with a fraction, thus: Degrees may also be expressed as a decimal fraction: Confusingly, the convention of negative for East is also sometimes seen.
The preferred convention—that East is positive—is consistent with a right-handed Cartesian coordinate systemwith the North Pole up. A specific longitude may then be combined with a specific latitude usually positive in the northern hemisphere to give a precise position on the Earth's surface. There is no other physical principle determining longitude directly but with time.3 Longitude and time differences
Longitude at a point may be determined by calculating the time difference between that at its location and Coordinated Universal Time UTC. In order to perform this calculation, however, a person needs to have a chronometer watch set to UTC and needs to determine local time by solar or astronomical observation.
The details are more complex than described here: Singularity and discontinuity of longitude[ edit ] Note that the longitude is singular at the Poles and calculations that are sufficiently accurate for other positions may be inaccurate at or near the Poles. An example is a calculation of east displacement by subtracting two longitudes, which gives the wrong answer if the two positions are on either side of this meridian.
To avoid these complexities, consider replacing latitude and longitude with another horizontal position representation in calculation.
Plate movement and longitude[ edit ] The Earth's tectonic plates move relative to one another in different directions at speeds on the order of 50 to mm per year. For example, the longitudinal difference between a point on the Equator in Uganda, on the African Plateand a point on the Equator in Ecuador, on the South American Plateis increasing by about 0.
These tectonic movements likewise affect latitude. If a global reference frame such as WGS84for example is used, the longitude of a place on the surface will change from year to year. To minimize this change, when dealing just with points on a single plate, a different reference frame can be used, whose coordinates are fixed to a particular plate, such as " NAD83 " for North America or " ETRS89 " for Europe.
To find their longitudehowever, 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 satelliteswas usually not possible at sea due to the ship's motion. The lunar distances methodinitially proposed by Johannes Werner inwas 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 The purpose of a chronometer is to measure accurately the time of a known fixed location, for example Greenwich Mean Time GMT.
This is particularly important for navigation. Knowing GMT at local noon allows a navigator to use the time difference between the ship's position and the Greenwich Meridian to determine the ship's longitude. In modern practice, a nautical almanac and trigonometric sight-reduction tables permit navigators to measure the SunMoonvisible planetsor any of 57 selected stars for navigation at any time that the horizon is visible. The creation of a timepiece which would work reliably at sea was difficult.
Until the 20th century, the best timekeepers were pendulum clocksbut both the rolling of a ship at sea and the up to 0. First marine chronometers[ edit ] Christiaan Huygensfollowing his invention of the pendulum clock inmade the first attempt at a marine chronometer in in Franceunder the sponsorship of Jean-Baptiste Colbert.
He obtained a patent for his invention from Colbert, but his clock remained imprecise at sea. During 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 what is known as Hooke's Law.
This was followed by a further theoretical description of a chronometer in works published by English scientist William Derham in 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. 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.
John Harrisona Yorkshire carpenter, submitted a project inand in completed a clock based on a pair of counter-oscillating weighted beams connected by springs whose motion was not influenced by gravity or the motion of a ship. His first two sea timepieces H1 and H2 completed in used this system, but he realised that they had a fundamental sensitivity to centrifugal forcewhich meant that they could never be accurate enough at sea.
Construction of his third machine, designated H3, in included novel circular balances and the invention of the bi-metallic strip and caged roller bearingsinventions which are still widely used.
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However, H3's circular balances still proved too inaccurate and he eventually abandoned the large machines. His design used a fast-beating balance wheel controlled by a temperature-compensated spiral spring.
These features remained in use until stable electronic oscillators allowed very accurate portable timepieces to be made at affordable cost. John Harrison 's H1 marine chronometer of Drawings of Harrison's H4 chronometer ofpublished in The principles of Mr Harrison's time-keeper, The modern chronometer[ edit ] In France,Pierre Le Roy invented the detent escapement characteristic of modern chronometers.
Ferdinand Berthoud in France, as well as Thomas Mudge in Britain also successfully produced marine timekeepers. The greatest strides toward practicality came at the hands of Thomas Earnshaw and John Arnoldwho in developed and patented simplified, detached, "spring detent" escapements  moved the temperature compensation to the balance, and improved the design and manufacturing of balance springs.
This combination of innovations served as the basis of marine chronometers until the electronic era.
Ferdinand Berthoud chronometer no. The new technology was initially so expensive that not all ships carried chronometers, as illustrated by the fateful last journey of the East Indiaman Arnistonshipwrecked with the loss of lives. Every day, ships would anchor briefly in the River Thames at Greenwich, waiting for the ball at the observatory to drop at precisely 1pm. In addition to setting their time before departing on a voyage, ship chronometers were also routinely checked for accuracy while at sea by carrying out lunar  or solar observations.
Mariners would use the chronometer to set a so-called hack watchwhich would be carried on deck to make the astronomical observations.
Though much less accurate and expensive than the chronometer, the hack watch would be satisfactory for a short period of time after setting it i. Although industrial production methods began revolutionizing watchmaking in the middle of the 19th century, chronometer manufacture remained craft-based much longer. Despite Hamilton's success, chronometers made in the old way never disappeared from the marketplace during the era of mechanical timekeepers.
Thomas Mercer Chronometers still makes chronometers to the present day. Without their accuracy and the accuracy of the feats of navigation that marine chronometers enabled, it is arguable that the ascendancy of the Royal Navyand by extension that of the British Empirewould not have occurred; the formation of the empire by wars and conquests of colonies abroad took place in a period in which British vessels had reliable navigation due to the chronometer, while their Portuguese, Dutch, and French opponents did not.
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Mechanical chronometers[ edit ] A chronometer mechanism diagrammed text is in German. Note fusee to transform varying spring tension to a constant force The crucial problem was to find a resonator that remained unaffected by the changing conditions met by a ship at sea.