Editing John Harrison (section)

== Later history ==
[[File:Martin Burgess - Clock B at the Royal Observatory - Greenwich.jpg|thumb|Clock B at the [[Royal Observatory, Greenwich]]|left|271x271px]]
After [[World War I]], Harrison's timepieces were rediscovered at the [[Royal Greenwich Observatory]] by retired naval officer [[Rupert T. Gould|Lieutenant Commander Rupert T. Gould]].

The timepieces were in a highly decrepit state and Gould spent many years documenting, repairing and restoring them, without compensation for his efforts.<ref>{{cite book | last = Betts| first = Jonathan| title = Time restored: The Harrison Timekeepers and R.T. Gould, the man who knew (almost) everything| publisher=Oxford University Press | year = 2006 | location = Oxford| page = 464| isbn = 978-0-19-856802-5}}</ref> Gould was the first to designate the timepieces from H1 to H5, initially calling them No.1 to No.5. Unfortunately, Gould made modifications and repairs that would not pass today's standards of good museum [[Conservation-restoration|conservation practice]], although most Harrison scholars give Gould credit for having ensured that the historical artifacts survived as working mechanisms to the present time. Gould wrote ''The Marine Chronometer'', published in 1923, which covered the history of chronometers from the [[Middle Ages]] to the 1920s, and which included detailed descriptions of Harrison's work and the subsequent evolution of the chronometer. The book remains the authoritative work on the marine chronometer. Today the restored H1, H2, H3, and H4 timepieces can be seen on display in the Royal Observatory at Greenwich. H1, H2, and H3 still work: H4 is kept in a stopped state because, unlike the first three, it requires oil for lubrication and so will degrade as it runs. H5 is owned by the [[Worshipful Company of Clockmakers]] of London, and was previously on display at the [[Clockmakers' Museum]] in the [[Guildhall, London]], as part of the Company's collection; since 2015 the collection has been displayed in the [[Science Museum, London]].

In the final years of his life, John Harrison wrote about his research into [[musical tuning]] and manufacturing methods for [[Bell (instrument)|bells]]. His tuning system (a [[Meantone temperament|meantone]] system derived from [[pi]]), is described in his pamphlet ''A Description Concerning Such Mechanism&nbsp;... (CSM)''.<ref name="CSM">{{Cite book |title=A Description concerning such Mechanism as will afford a nice, or true Mensuration of Time; together with Some Account of the Attempts for the Discovery of the Longitude by the Moon; and also An Account of the Discovery of the Scale of Musick |url=http://www.hsn161.com/HSN/CSM.pdf |first=John |last=Harrison |author-link=John Harrison |place=London |year=1775}}</ref> The system challenged the traditional view that [[harmonics]] occur at integer [[frequency]] ratios and in consequence all music using this tuning produces [[Beat (acoustics)|low-frequency beating]]. In 2002, Harrison's last manuscript, ''A true and short, but full Account of the Foundation of Musick, or, as principally therein, of the Existence of the Natural Notes of Melody'', was rediscovered in the US [[Library of Congress]]. His theories on the mathematics of bell manufacturing (using "Radical Numbers") are yet to be clearly understood.<ref>{{cite web|url=http://www.lucytune.com/academic/manuscript_search.html |title=LucyTuning*LucyScaleDevelopments*LucyTuned Lullabies*Pi tuning*John Longitude Harrison |publisher=Lucytune.com |access-date=28 September 2012}}</ref>

One of the controversial claims of his last years was that of being able to build a land clock more accurate than any competing design. Specifically, he claimed to have designed a clock capable of keeping accurate time to within one second over a span of 100 days.<ref name=CSM />{{Rp|25–41}} At the time, such publications as ''The London Review of English and Foreign Literature'' ridiculed Harrison for what was considered an outlandish claim. Harrison drew a design but never built such a clock himself, but in 1970 [[Martin Burgess]], a Harrison expert and himself a clockmaker, studied the plans and endeavored to build the timepiece as drawn. He built two versions, dubbed Clock A and Clock B. Clock A became the Gurney Clock which was given<!--by Barclay's Bank, not Burgess, but this is getting too far off topic already--> to the city of [[Norwich]] in 1975, while Clock B lay unfinished in his workshop for decades until it was acquired in 2009 by [[Donald Saff]]. The completed Clock B was submitted to the [[National Maritime Museum]] in [[Greenwich, London|Greenwich]] for further study. It was found that Clock B could potentially meet Harrison's original claim, so the clock's design was carefully checked and adjusted. Finally, over a 100-day period from 6 January to 17 April 2015, Clock B was secured in a transparent case in the Royal Observatory and left to run untouched, apart from regular winding. Upon completion of the run, the clock was measured to have lost only 5/8 of a second, meaning Harrison's design was fundamentally sound. If we ignore the fact that this clock uses materials such as [[duraluminium]] and [[invar]] unavailable to Harrison, had it been built in 1762, the date of Harrison's testing of his H4, and run continuously since then without correction, it would now ({{CURRENTMONTHNAME}} {{CURRENTYEAR}}) be slow by just <!--Noon, 26 March 1762 is 75885.5 days = 6556507200 seconds prior to 1 January 1970.  5/8 second / 100 days = 72.338 ppb slow.-->{{#expr:trunc ((({{#time:U}}+6556507200)*72.338e-9 round 0)/60)}} minutes and {{#expr:(({{#time:U}}+6556507200)*72.338e-9 round 0) mod 60}} seconds. [[Guinness World Records]] has declared Martin Burgess' Clock B the "most accurate mechanical clock with a pendulum swinging in free air."<ref name="The Observer 19 April 2015">{{cite news |title=Clockmaker John Harrison vindicated 250 years after 'absurd' claims |url=https://www.theguardian.com/science/2015/apr/19/clockmaker-john-harrison-vindicated-250-years-absurd-claims |last=McKie |first=Robin |newspaper=[[The Observer]] |date=2015-04-18 |page=7 |access-date=2015-04-23}}</ref>