Thomas Earnshaw
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Thomas Earnshaw (4 February 1749 – 1 March 1829) was an English
watchmaker A watchmaker is an artisan who makes and repairs watches. Since a majority of watches are now factory-made, most modern watchmakers only repair watches. However, originally they were master craftsmen who built watches, including all their par ...
who, following John Arnold's earlier work, further simplified the process of
marine chronometer 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 t ...
production, making them available to the general public. He is also known for his improvements to the transit
clock A clock or chronometer is a device that measures and displays time. The clock is one of the oldest Invention, human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, a ...
at the
Royal Greenwich Observatory The Royal Observatory, Greenwich (ROG; known as the Old Royal Observatory from 1957 to 1998, when the working Royal Greenwich Observatory, RGO, temporarily moved south from Greenwich to Herstmonceux) is an observatory situated on a hill in G ...
in London and his invention of a chronometer
escapement An escapement is a mechanical linkage in mechanical watches and clocks that gives impulses to the timekeeping element and periodically releases the gear train to move forward, advancing the clock's hands. The impulse action transfers energy to t ...
and a form of bimetallic compensation balance.Thomas Earnshaw
at ''Encyclopædia Britannica Online''.
In 1780, he devised a modification to the detached chronometer
escapement An escapement is a mechanical linkage in mechanical watches and clocks that gives impulses to the timekeeping element and periodically releases the gear train to move forward, advancing the clock's hands. The impulse action transfers energy to t ...
, the detent being mounted on a spring instead of on pivots. This spring detent escapement was patented by Thomas Wright (for whom he worked) in 1783. Whilst initially the design was crude and unsuccessful, with modifications it later became the standard form in marine chronometers,Details on Earnshaw's spring indent escapement
following the invention of the detent escapement by Pierre Le Roy in 1748. John Arnold also invented a similar escapement in 1782. In 1805, Earnshaw and Arnold were granted awards by the
Board of Longitude Board or Boards may refer to: Flat surface * Lumber, or other rigid material, milled or sawn flat ** Plank (wood) ** Cutting board ** Sounding board, of a musical instrument * Cardboard (paper product) * Paperboard * Fiberboard ** Hardboard ...
for their improvements to chronometers; Earnshaw received £2500 and John Arnold's son John Roger Arnold received £1672. The bimetallic compensation balance and the spring detent escapement in the forms designed by Earnshaw have been used essentially universally in
marine chronometer 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 t ...
s since then, and for this reason Earnshaw is generally regarded as one of the pioneers of chronometer development. Although he was principally a watchmaker, he did not shy away from building clocks. When asked by
Nevil Maskelyne Nevil Maskelyne (; 6 October 1732 – 9 February 1811) was the fifth British Astronomer Royal. He held the office from 1765 to 1811. He was the first person to scientifically measure the mass of the planet Earth. He created '' The Nautical Al ...
, he produced a clock for the Armagh Observatory. This clock incorporated Earnshaw's new design of escapement and had a number of novel features, including an airtight case (designed to reduce dust and draughts). It was highly praised by John Thomas Romney Robinson in the 19th century, who at that time believed it to be the most accurate clock in the world. In 1794, its purchase price was £100 and Earnshaw charged £100 to travel with it to Armagh and set it up in the new Observatory.Information o
Earnshaw's first clock
at the Armagh Observatory website.
The Observatory also purchased Earnshaw's second clockInformation o

at the Armagh Observatory website.
which was operated at sidereal rate with Edward Troughton's Equatorial Telescope.


Chronometers on notable voyages

In July, 1791, Captain
William Bligh William Bligh (9 September 1754 – 7 December 1817) was a Vice-admiral (Royal Navy), Royal Navy vice-admiral and colonial administrator who served as the governor of New South Wales from 1806 to 1808. He is best known for his role in the Muti ...
purchased on behalf of the Admiralty Earnshaw's chronometer no. 1503 at a price of for an expedition he was to command in to transport
breadfruit Breadfruit (''Artocarpus altilis'') is a species of flowering tree in the mulberry and jackfruit family ( Moraceae) believed to have been selectively bred in Polynesia from the breadnut ('' Artocarpus camansi''). Breadfruit was spread into ...
plants from
Tahiti Tahiti (; Tahitian language, Tahitian , ; ) is the largest island of the Windward Islands (Society Islands), Windward group of the Society Islands in French Polynesia, an overseas collectivity of France. It is located in the central part of t ...
to the
West Indies The West Indies is an island subregion of the Americas, surrounded by the Atlantic Ocean, North Atlantic Ocean and the Caribbean Sea, which comprises 13 independent island country, island countries and 19 dependent territory, dependencies in thr ...
. This was the second expedition that Bligh had undertaken with this mission. The first expedition was with HMS ''Bounty'' which had ended in the infamous
mutiny Mutiny is a revolt among a group of people (typically of a military or a crew) to oppose, change, or remove superiors or their orders. The term is commonly used for insubordination by members of the military against an officer or superior, ...
led by Fletcher Christian and from which Bligh returned to England only with the greatest of difficulties. The second expedition, however, was entirely successful. Around 1796 Earnshaw, who had temporarily lost interest in the Board of Longitude reward, was tempted back by the failure of Josiah Emery to win it. Earnshaw had a low opinion of Emery's chronometers and claimed that an already existing chronometer of his, no. 265, could outperform Emery's even though it had just returned from a voyage to the West Indies and had not been cleaned (dirty oil has an adverse effect on the going of a chronometer). Earnshaw was easily proved right in this and his chronometer had a good average rate over a 12-month trial. However, he failed to win any reward because the method of rating required that the rate of the piece in the first month be used as the baseline for the trial rather than the absolute timekeeping of the instrument. Ironically, this method had originally been proposed by Earnshaw's ally Maskelyne. In June 1801,
Matthew Flinders Captain (Royal Navy), Captain Matthew Flinders (16 March 1774 – 19 July 1814) was a British Royal Navy officer, navigator and cartographer who led the first littoral zone, inshore circumnavigate, circumnavigation of mainland Australia, then ...
' ship, HMS ''Investigator'', carried two boxed Timekeepers by Earnshaw E520 and E543, at a cost of 100 Guineas each. ''Investigator'' also carried two of Arnled's timekeepers on the first
circumnavigation Circumnavigation is the complete navigation around an entire island, continent, or astronomical object, astronomical body (e.g. a planet or natural satellite, moon). This article focuses on the circumnavigation of Earth. The first circumnaviga ...
and mapping of the coastline of
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
. The chronometer, E520, was mounted in a wooden box with gimbals to compensate for the motion of the ship. Flinders went to shore regularly to check the settings of the chronometers against the stars. The Earnshaw chronometer was the only one working at the end of the journey, causing Flinders to refer to it in his book '' A Voyage to Terra Australis'' as "this excellent timekeeper". Flinders was taken prisoner-of-war by the French in
Mauritius Mauritius, officially the Republic of Mauritius, is an island country in the Indian Ocean, about off the southeastern coast of East Africa, east of Madagascar. It includes the main island (also called Mauritius), as well as Rodrigues, Ag ...
. In 1805 Captain Aken, a fellow prisoner, was released and returned to England. Flinders gave him the chronometers to return to the
Greenwich Observatory The Royal Observatory, Greenwich (ROG; known as the Old Royal Observatory from 1957 to 1998, when the working Royal Greenwich Observatory, RGO, temporarily moved south from Greenwich to Herstmonceux) is an observatory situated on a hill in G ...
. By some unknown sequence of events, the Earnshaw 520 was sold to an Australian collector and in 1937 became the property of the Museum of Applied Arts and Sciences (
Powerhouse Museum The Powerhouse Museum, formerly known as the Museum of Applied Arts & Sciences (MAAS), is a collection of 4 museums in Sydney, owned by the Government of New South Wales. Powerhouse is a contemporary museum of applied arts and sciences, explori ...
) in
Sydney Sydney is the capital city of the States and territories of Australia, state of New South Wales and the List of cities in Australia by population, most populous city in Australia. Located on Australia's east coast, the metropolis surrounds Syd ...
. It was not until 1976 that it was identified as the chronometer of Flinders' historic journey. Between 1831 and 1836, chronometer no. 509 was carried on HMS ''Beagle'' on a voyage to circumnavigate the globe and establish, for the first time, a chain of points around the world of accurately-known longitude. The ship was commanded by Captain
Robert FitzRoy Vice-Admiral Robert FitzRoy (5 July 1805 – 30 April 1865) was an English officer of the Royal Navy, politician and scientist who served as the second governor of New Zealand between 1843 and 1845. He achieved lasting fame as the captain of ...
, a future Vice-Admiral and founder of the
Meteorological Office The Met Office, until November 2000 officially the Meteorological Office, is the United Kingdom's national weather and climate service. It is an executive agency and trading fund of the Department for Science, Innovation and Technology and ...
. This was only one of many chronometers carried by the ''Beagle'' since great accuracy was required for this task. This was also the voyage that carried
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...
who was afterwards inspired to write his book about the theory of
evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...
, ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life'')The book's full original title was ''On the Origin of Species by M ...
''. The chronometer is object 91 in the
BBC Radio 4 BBC Radio 4 is a British national radio station owned and operated by the BBC. The station replaced the BBC Home Service on 30 September 1967 and broadcasts a wide variety of spoken-word programmes from the BBC's headquarters at Broadcasti ...
series '' A History of the World in 100 Objects''."Ship's chronometer from HMS ''Beagle''"
"Ship's chronometer from HMS Beagle"
/ref>


References

{{DEFAULTSORT:Earnshaw, Thomas 1749 births 1829 deaths English watchmakers (people) People from Ashton-under-Lyne British scientific instrument makers