Editing John Harrison (section)

== Longitude watches ==
<!-- [[H6]] links to this section -->[[File:H4 low 250.jpg|thumb|220px|Harrison's "sea watch" No. 1 (H4), with winding crank]]
After steadfastly pursuing various methods during thirty years of experimentation, Harrison found to his surprise that some of the watches made by Graham's successor [[Thomas Mudge (horologist)|Thomas Mudge]] kept time just as accurately as his huge sea clocks.{{Citation needed|date=January 2013}} It is possible that Mudge was able to do this after the early 1740s thanks to the availability of the new "Huntsman" or [[Crucible steel|"Crucible" steel]] first produced by [[Benjamin Huntsman]] sometime in the early 1740s, which enabled harder [[pinion]]s but more importantly a tougher and more highly polished cylinder escapement to be produced.<ref>{{cite book | last = Wayman| first = Michael L. | title = The Ferrous Metallurgy of Early Clocks and Watches | publisher=British Museum | year = 2000 }}</ref>
Harrison then realized that a mere watch after all could be made accurate enough for the task and was a far more practical proposition for use as a marine timekeeper. He proceeded to redesign the concept of the watch as a timekeeping device, basing his design on sound scientific principles.

==="Jefferys" watch===
He had already in the early 1750s designed a precision watch for his own use, which was made for him by the watchmaker [[John Jefferys (clockmaker)|John Jefferys]] {{circa}} 1752–1753. This watch incorporated a novel frictional rest escapement and was not only the first to have a compensation for temperature variations but also contained the first miniature ''[[going train]] [[Fusee (horology)|fusee]]'' of Harrison's design which enabled the watch to continue running whilst being wound. These features led to the very successful performance of the "Jefferys" watch, which Harrison incorporated into the design of two new timekeepers which he proposed to build. These were in the form of a large watch and another of a smaller size but similar pattern. However, only the larger No. 1 watch (or "H4" as it is sometimes called) appears to have been finished (see the reference to "H4" below). Aided by some of London's finest workmen, he proceeded to design and make the world's first successful marine timekeeper that allowed a navigator to accurately assess his ship's position in [[longitude]]. Importantly, Harrison showed everyone that it could be done by using a watch to calculate longitude.<ref>{{cite web | title = Harrison's Marine timekeeper (H4) | publisher=[[National Maritime Museum]] | url = http://collections.rmg.co.uk/collections/objects/79142.html | access-date = 25 February 2008}}</ref> This was to be Harrison's masterpiece – an instrument of beauty, resembling an oversized [[pocket watch]] from the period. It is engraved with Harrison's signature, marked Number 1 and dated AD 1759.

=== H4 ===
[[File:Harrison H4 clockwork 1.jpg|thumb|upright=1.3|right|The clockwork in Harrison's H4 watch]][[file:Harrison H4 clock in The principles of Mr Harrison's time-keeper 1767.jpg|thumb|Drawings of Harrison's H4 chronometer of 1761, published in ''The principles of Mr Harrison's time-keeper'', 1767.<ref>''[https://books.google.com/books?id=aB8OAAAAQAAJ The principles of Mr Harrison's time-keeper]''</ref>]]
Harrison's first "sea watch" (now known as H4) is housed in silver pair cases some {{convert|5.2|in|cm}} in diameter. The clock's [[Movement (clockwork)|movement]] is highly complex for the period, resembling a larger version of the then-current conventional movement. A coiled steel spring inside a brass mainspring barrel provides 30 hours of power. That is covered by the fusee barrel which pulls a chain wrapped around the conically shaped pulley known as the fusee. The fusee is topped by the winding square (requiring separate key). The great wheel attached to the base of this fusee transmits power to the rest of the movement. The fusee contains the [[maintaining power]], a mechanism for keeping the H4 going while being wound. From Gould:<ref name="gould" /> {{Blockquote|The escapement is a modification of the "verge" fitted to... the common watches of Harrison's day. But the modifications are extensive. The pallets are very small, and have their faces set parallel, instead of at the usual angle of 95° or so. Moreover, instead of being steel, they are of diamond, and their backs are shaped to cycloidal curves... The action of this escapement is quite different from that of the verge, which it appears to resemble. In that escapement, the teeth of the crown wheel act only upon the faces of the pallets. But in this, as will be seen from the points of the teeth rest, for a considerable portion of the supplementary arc—from 90° to 145° (limit of banking) past the dead point—upon the ''backs'' of the pallets, and tend to assist the balance towards the extreme of its swing and to retard its return. This escapement is obviously a great improvement upon the verge, as the train has far less power over the motions of the balance. The latter is no longer checked in its swing by a force equal to that which originally impelled it, but by the balance spring, assisted only by the friction between the tooth and the back of the pallet.}}

In comparison, the verge's escapement has a recoil with a limited balance arc and is sensitive to variations in driving torque. According to a review by H. M. Frodsham of the movement in 1878, H4's escapement had "a good deal of 'set' and not so much recoil, and as a result the impulse came very near to a double chronometer action".<ref>Harrison M. Frodsham, 'Some Materials for a Resume of Remontoires', ''Horological Journal'', Vol. 20 (1877-78), p120-122</ref>

The D-shaped pallets of Harrison's escapement are both made of [[diamond]], approximately 2&nbsp;mm long with the curved side radius of 0.6&nbsp;mm, a considerable feat of manufacture at the time.<ref>{{Cite web|url=https://watchesbysjx.com/2019/09/john-harrison-marine-chronometer-h4-diamond-pallets.html|title=In-Depth: The Microscopic Magic of H4, Harrison's First Sea Watch. A heart of diamond.|last=Lake|first=Tim|website=WatchesbySJX|access-date=2 September 2019}}</ref> For technical reasons the balance was made much larger than in a conventional watch of the period, {{convert|2.2|in}} in diameter weighing {{convert|28+5/8|gr||adj=pre|Troy}} and the vibrations controlled by a flat spiral steel spring of three turns with a long straight tail. The spring is tapered, being thicker at the stud end and tapering toward the collet at the centre. The movement also has centre seconds motion with a sweep seconds hand.

The Third Wheel is equipped with internal teeth and has an elaborate bridge similar to the pierced and engraved bridge for the period. It runs at 5 beats (ticks) per second, and is equipped with a tiny {{frac|7|1|2}} second [[remontoire]]. A balance-brake, activated by the position of the fusee, stops the watch half an hour before it is completely run down, in order that the remontoire does not run down also. Temperature compensation is in the form of a 'compensation curb' (or 'Thermometer Kirb' as Harrison called it). This takes the form of a bimetallic strip mounted on the regulating slide, and carrying the curb pins at the free end. During its initial testing, Harrison dispensed with this regulation using the slide, but left its indicating dial or figure piece in place. This first watch took six years to construct, following which the Board of Longitude determined to trial it on a voyage from Portsmouth to Kingston, [[Jamaica]]. For this purpose it was placed aboard the 50-gun {{HMS|Deptford|1732|6}}, which set sail from Portsmouth on 18 November 1761.<ref name="Clowes">{{cite book|last=Clowes|first=William Laird|title=The Royal Navy: A History From the Earliest Times to the Present|volume=3|publisher=Sampson, Low, Marston and Company|year=1898|location=London|oclc=645627800}}</ref>{{rp|13–14}} Harrison, by then 68 years old, sent it on this transatlantic trial in the care of his son, [[William Harrison (instrument maker)|William]]. The watch was tested before departure by Robertson, Master of the Academy at Portsmouth, who reported that on 6 November 1761 at noon it was 3 seconds slow, having lost 24 seconds in 9 days on mean solar time. The daily rate of the watch was therefore fixed as losing {{frac|24|9}} seconds per day.<ref name="Rees">Rees's Clocks Watches and Chronometers, 1819–20, David & Charles reprint 1970</ref>

When ''Deptford'' reached its destination, after correction for the initial error of 3 seconds and accumulated loss of 3 minutes 36.5 seconds at the daily rate over the 81 days and 5 hours of the voyage,<ref name="Rees" /> the watch was found to be 5 seconds slow compared to the known longitude of Kingston, corresponding to an error in longitude of 1.25 minutes, or approximately one nautical mile.<ref name=gould>{{cite book | url=http://fer3.com/arc/imgx/marinechronomete00gouluoft_b.pdf | author=Gould, Rupert T. | author-link = Rupert Gould | title=The Marine Chronometer. Its History and Development | location=London | publisher=J. D. Potter | year=1923 | isbn=0-907462-05-7}}</ref>{{rp|56}} William Harrison returned aboard the 14-gun {{HMS|Merlin|1757|6}}, reaching England on 26 March 1762 to report the successful outcome of the experiment.<ref name=Clowes /> Harrison senior thereupon waited for the £20,000 prize, but the Board were persuaded that the accuracy could have been just luck and demanded another trial. The Board were also not convinced that a timekeeper which took six years to construct met the test of practicality required by the [[Longitude Act 1714|Longitude Act]]. The Harrisons were outraged and demanded their prize, a matter that eventually worked its way to [[Parliament of the United Kingdom|Parliament]], which offered £5,000 for the design. The Harrisons refused but were eventually obliged to make another trip to [[Bridgetown]] on the island of [[Barbados]] to settle the matter.

At the time of this second trial, another method for measuring longitude was ready for testing: the [[Method of Lunar Distances]]. The Moon moves fast enough, some thirteen degrees a day, to easily measure the movement from day to day. By comparing the angle between the Moon and the Sun for the day one left for Britain, the "proper position" (how it would appear in [[Greenwich]], England, at that specific time) of the Moon could be calculated. By comparing this with the angle of the Moon over the horizon, the longitude could be calculated. During Harrison's second trial of his 'sea watch' (H4), [[Nevil Maskelyne]] was asked to accompany [[HMS Tartar (1756)|HMS ''Tartar'']] and test the Lunar Distances system. Once again the watch proved extremely accurate, keeping time to within 39 seconds, corresponding to an error in the longitude of Bridgetown of less than {{convert|10|mi|km}}.<ref name="gould" />{{rp|60}} Maskelyne's measures were also fairly good, at {{convert|30|mi|km}}, but required considerable work and calculation in order to use. At a meeting of the Board in 1765 the results were presented, but they again attributed the accuracy of the measurements to luck. Once again the matter reached Parliament, which offered £10,000 in advance and the other half once he turned over the design to other watchmakers to duplicate.<ref>In 1767, the Board of Longitude published a detailed description of Harrison's H4 watch:  {{cite book |last1=The Commissioners of Longitude |title=The Principles of Mr. Harrison's Time-Keeper, with Plates of the Same |date=1767 |publisher=W. Richardson and S. Clark |location=London, England |url=https://archive.org/details/principlesmrhar00unkngoog/page/n6}}</ref> In the meantime Harrison's watch would have to be turned over to the Astronomer Royal for long-term on-land testing.[[File:Harrison's Chronometer H5.JPG|thumb|upright=1.3|Harrison's Chronometer H5, (Collection of the [[Worshipful Company of Clockmakers]]), in the [[Science Museum, London]]]]

Unfortunately, Nevil Maskelyne had been appointed [[Astronomer Royal]] on his return from Barbados, and was therefore also placed on the Board of Longitude. He returned a report of the watch that was negative, claiming that its "going rate" (the amount of time it gained or lost per day) was due to inaccuracies cancelling themselves out, and refused to allow it to be factored out when measuring longitude. Consequently, this first Marine Watch of Harrison's failed the needs of the Board despite the fact that it had succeeded in two previous trials.
Harrison began working on his second 'sea watch' (H5) while testing was conducted on the first, which Harrison felt was being held hostage by the Board. After three years he had had enough; Harrison felt "extremely ill used by the gentlemen who I might have expected better treatment from"<ref>{{Cite journal |last=Burkholder |first=Ruth |year=1983 |title=Solving the Problem of Longitude |url=https://www.captaincooksociety.com/cooks-life/people/cooks-officers-and-crew-and-contemporaries/john-harrison-solving-the-problem-of-longitude |journal=Cook's Log |publisher=Captain Cook Society |volume=6 |issue=4 |pages=222–224}}</ref> and decided to enlist the aid of King [[George III of Great Britain|George III]]. He obtained an audience with the King, who was extremely annoyed with the Board. King George tested the watch No. 2 (H5) himself at the palace and after ten weeks of daily observations between May and July in 1772, found it to be accurate to within one third of one second per day. King George then advised Harrison to petition Parliament for the full prize after threatening to appear in person to dress them down. Finally in 1773, when he was 80 years old, Harrison received a monetary award in the amount of £8,750 from Parliament for his achievements, but he never received the official award (which was never awarded to anyone). He was to live for just three more years.

In total, Harrison received £23,065 for his work on chronometers. He received £4,315 in increments from the Board of Longitude for his work, £10,000 as an interim payment for H4 in 1765 and £8,750 from Parliament in 1773.<ref>{{cite book | last = Varzeliotis| first = A.N. Thomas | title = Time Under Sail: The Very Human Story of the Marine Chronometer | publisher=Alcyone Books | year = 1998 | isbn = 0-921081-10-3}}</ref> This gave him a reasonable income for most of his life (equivalent to roughly £450,000 per year in 2007, though all his costs, such as materials and subcontracting work to other horologists, had to come out of this). He became the equivalent of a multi-millionaire (in today's terms) in the final decade of his life. Captain [[James Cook]] used [[Larcum Kendall#K1|K1]], a copy of H4, on his second and third voyages, having used the [[lunar distance method]] on his first voyage.<ref>Captain James Cook, Richard Hough, Holder and Stroughton 1994.pp 192–193 {{ISBN|0-340-58598-6}}</ref> K1 was made by [[Larcum Kendall]], who had been apprenticed to [[John Jefferys (clockmaker)|John Jefferys]]. Cook's log is full of praise for the watch and the charts of the southern Pacific Ocean he made with its use were remarkably accurate.  [[Larcum Kendall#K2|K2]] was loaned to Lieutenant [[William Bligh]], commander of [[HMS Bounty|HMS ''Bounty'']], but it was retained by [[Fletcher Christian]] following the infamous [[Mutiny on the Bounty|mutiny]]. It was not recovered from [[Pitcairn Island]] until 1808, when it was given to Captain [[Mayhew Folger]], and then passed through several hands before reaching the [[National Maritime Museum]] in London.

Initially, the cost of these chronometers was quite high (roughly 30% of a ship's cost). However, over time, the costs dropped to between £25 and £100 (half a year's to two years' salary for a skilled worker) in the early 19th century.<ref name="landes">{{cite book| last = Landes| first = David S.| title = Revolution in Time| publisher = Belknap Press of Harvard University Press| year = 1983| location = Cambridge, Massachusetts| url = https://archive.org/details/revolutionintime00land_1| isbn = 0-674-76800-0}}</ref><ref>{{cite book | last = Mercer| first = Vaudrey | title = John Arnold & Son, Chronometer Makers, 1762–1843 | publisher=The Antiquarian Horological Society | year = 1972 }}</ref> Many historians point to relatively low production volumes over time as evidence that the chronometers were not widely used. However, Landes<ref name="landes" /> points out that the chronometers lasted for decades and did not need to be replaced frequently–indeed the number of makers of marine chronometers reduced over time due to the ease in supplying the demand even as the merchant marine expanded.<ref name="king">{{cite book | last = King| first = Dean| title = A Sea of Words | publisher=Henry Holt and Co. | year = 2000 | location = New York| isbn = 978-0-8050-6615-9}} This book has a table showing that at the peak just prior to the [[War of 1812]], Britain's [[Royal Navy]] had almost 1,000 ships. By 1840, this number had reduced to only 200. Even though the navy only officially equipped their vessels with chronometers after 1825, this shows that the number of chronometers required by the navy was shrinking in the early 19th century.</ref><ref name="Mörzer Bruyns">{{cite encyclopedia | last=Mörzer Bruyns | first=Willem F. J. | editor1-last = Anderson | editor1-first = R. G. W. |editor2-last = Bennett | editor2-first = J. A. | editor3-last = Ryan | editor3-first = W. F. | encyclopedia= Making Instruments Count: Essays on Historical Scientific Instruments Presented to Gerard L'Estrange Turner | title = The Astronomical Clocks of Andreas Hohwü: A Checklist | year= 1993 | publisher= Varorium | location = Aldershot | isbn = 0-86078-394-4 | pages = 454–470}} Mörzer Bruyns identifies a recession starting around 1857 that depressed shipping and the need for chronometers.</ref> Also, many merchant mariners would make do with a deck chronometer at half the price. These were not as accurate as the boxed marine chronometer but were adequate for many. While the Lunar Distances method would complement and rival the marine chronometer initially, the chronometer would overtake it in the 19th century. The more accurate Harrison timekeeping device led to the much-needed precise calculation of [[longitude]], making the device a fundamental key to the modern age. After Harrison, the marine timekeeper was reinvented yet again by [[John Arnold (watchmaker)|John Arnold]], who, while basing his design on Harrison's most important principles, at the same time simplified it enough for him to produce equally accurate but far less costly marine chronometers in quantity from around 1783. Nonetheless, for many years even towards the end of the 18th century, chronometers were expensive rarities, as their adoption and use proceeded slowly due to the high expense of precision manufacturing. The expiry of Arnold's patents at the end of the 1790s enabled many other watchmakers including [[Thomas Earnshaw]] to produce chronometers in greater quantities at less cost even than those of Arnold.

By the early 19th century, navigation at sea without one was considered unwise to unthinkable. Using a chronometer to aid navigation simply saved lives and ships – the insurance industry, self-interest, and common sense did the rest in making the device a universal tool of maritime trade.