Editing Longitude (section)

===The Chronometer===
[[File:Harrison H4 clockwork 1.jpg|thumb|upright=1.2|The clockwork in [[John Harrison]]'s [[Marine_chronometer#First examples|H4 marine chronometer]] on display at the [[Royal Observatory, Greenwich]]]]
In response to the problems of navigation, a number of European maritime powers offered prizes for a method to determine longitude at sea. The best-known of these is the [[Longitude Act]] passed by the British parliament in 1714.<ref name="Siegel">{{cite journal |last1=Siegel |first1=Jonathan R. |title=Law and Longitude |journal=Tulane Law Review |date=2009 |volume=84 |pages=1–66}}</ref>{{rp|8}} It offered two levels of rewards, for solutions within 1° and 0.5°. Rewards were given for two solutions: lunar distances, made practicable by the tables of [[Tobias Mayer]]<ref name="Forbes2006">{{cite journal |last1=Forbes |first1=Eric Gray |title=Tobias Mayer's lunar tables|journal=Annals of Science |volume=22 |issue=2 |year=2006 |pages=105–116 |issn=0003-3790|doi=10.1080/00033796600203075}}</ref> developed into an [[nautical almanac]] by the [[Astronomer Royal]] [[Nevil Maskelyne]]; and for the [[chronometers]] developed by the Yorkshire carpenter and clock-maker [[John Harrison]]. Harrison built five chronometers over more than three decades. This work was supported and rewarded with thousands of pounds from the Board of Longitude,<ref>{{Cite web|date=2012-03-07|title=There was no such thing as the Longitude Prize|url=https://www.rmg.co.uk/discover/behind-the-scenes/blog/there-was-no-such-thing-longitude-prize|access-date=2021-01-27|website=Royal Museums Greenwich|language=en|archive-date=2023-01-22|archive-url=https://web.archive.org/web/20230122155948/https://www.rmg.co.uk/stories/blog/there-was-no-such-thing-longitude-prize|url-status=live}}</ref> but he fought to receive money up to the top reward of £20,000, finally receiving an additional payment in 1773 after the intervention of Parliament.{{r|"Siegel"|p=26}} It was some while before either method became widely used in navigation. In the early years, chronometers were very expensive, and the calculations required for lunar distances were still complex and time-consuming. Lunar distances came into general use after 1790.<ref name="Wess2015">{{cite book|title=Navigational Enterprises in Europe and its Empires, 1730-1850 |editor1-last=Dunn |editor1-first=Richard |editor2-last=Higgitt |editor2-first=Rebekah |last1=Wess|first1=Jane|chapter=Navigation and Mathematics: A Match Made in the Heavens?|year=2015|pages=201–222|publisher=Palgrave Macmillan UK |location=London |doi=10.1057/9781137520647_11|isbn=978-1-349-56744-7 }}</ref> Chronometers had the advantages that both the observations and the calculations were simpler, and as they became cheaper in the early 19th century they started to replace lunars, which were seldom used after 1850.<ref name="Littlehales">{{cite journal |last1=Littlehales |first1=G.W. |title=The Decline of the Lunar Distance for the Determination of the Time and Longitude at |journal=Bulletin of the American Geographical Society |date=1909 |volume=41 |issue=2 |pages=83–86 |doi=10.2307/200792 |jstor=200792 |url=https://archive.org/details/jstor-200792}}</ref>

The first working [[Telegraphy|telegraphs]] were established in Britain by [[Charles Wheatstone|Wheatstone]] and [[William Fothergill Cooke|Cooke]] in 1839, and in the US by [[Samuel Morse|Morse]] in 1844. It was quickly realised that the telegraph could be used to transmit a time signal for longitude determination.<ref name="Walker 1850">{{cite journal |last1=Walker |first1=Sears C |title=Report on the experience of the Coast Survey in regard to telegraph operations, for determination of longitude &c. |journal=American Journal of Science and Arts |date=1850 |volume=10 |issue=28 |pages=151–160 |url=https://archive.org/details/appendix-telegraphic-longitude-the-american-journal-of-science-and-arts }}</ref> The method was soon in practical use for longitude determination, especially in North America, and over longer and longer distances as the telegraph network expanded, including western Europe with the completion of transatlantic cables. The United States Coast Survey, renamed the [[United States Coast and Geodetic Survey]] in 1878, was particularly active in this development, and not just in the United States. The Survey established chains of mapped locations through Central and South America, and the West Indies, and as far as Japan and China in the years 1874–90. This contributed greatly to the accurate mapping of these areas.<ref name="Knox">{{cite journal |last1=Knox |first1=Robert W. |title=Precise Determination of Longitude in the United States |journal=Geographical Review |date=1957 |volume=47 |issue=4 |pages=555–563 |doi=10.2307/211865 |jstor=211865|bibcode=1957GeoRv..47..555K }}</ref><ref name="Green1883">{{cite book |last1=Green |first1=Francis Mathews |last2=Davis |first2=Charles Henry |last3=Norris |first3=John Alexander |title=Telegraphic Determination of Longitudes in Japan, China, and the East Indies: Embracing the Meridians of Yokohama, Nagasaki, Wladiwostok, Shanghai, Amoy, Hong-Kong, Manila, Cape St. James, Singapore, Batavia, and Madras, with the Latitude of the Several Stations |date=1883 |publisher=US Hydrographic Office |location=Washington |url=https://archive.org/details/in.ernet.dli.2015.177254}}</ref>

While mariners benefited from the accurate charts, they could not receive telegraph signals while under way, and so could not use the method for navigation. This changed when wireless telegraphy (radio) became available in the early 20th century.<ref name="Munro1902">{{cite journal |last1=Munro |first1=John |s2cid=4021629 |title=Time-Signals by Wireless Telegraphy |journal=Nature |volume=66 |issue=1713 |year=1902 |pages=416 |issn=0028-0836 |doi=10.1038/066416d0 |bibcode=1902Natur..66..416M |url=https://zenodo.org/record/2080631 |access-date=2020-09-26 |archive-date=2021-04-14 |archive-url=https://web.archive.org/web/20210414140852/https://zenodo.org/record/2080631 |url-status=live |doi-access=free }}</ref> Wireless time signals for the use of ships were transmitted from [[Halifax, Nova Scotia]], starting in 1907<ref name="Hutchnson">{{cite journal |last1=Hutchinson |first1=D.L. |title=Wireless Time Signals from the St. John Observatory of the Canadian Meteorological Service. |journal=Proceedings and Transactions of the Royal Society of Canada |date=1908 |volume=Ser. 3 Vol. 2 |pages=153–154 |url=https://archive.org/details/hutchinson-1908-proceedingstrans-32roya}}</ref> and from the [[Eiffel Tower]] in Paris from 1910.<ref name="Lockyer1913">{{cite journal|last1=Lockyer|first1=William J. S.|s2cid=3977506|title=International Time and Weather Radio-Telegraphic Signals |journal=Nature |volume=91 |issue=2263 |year=1913 |pages=33–36 |issn=0028-0836 |doi=10.1038/091033b0 |bibcode=1913Natur..91...33L |doi-access=free}}</ref> These signals allowed navigators to check and adjust their chronometers frequently.<ref name="Zimmerman">{{cite web |last1=Zimmerman |first1=Arthur E. |title=The first wireless time signals to ships at sea |url=https://www.antiquewireless.org/wp-content/uploads/50-the_first_wireless_time_signals_to_ships_at_sea.pdf |website=antiquewireless.org |publisher=Antique Wireless Association |access-date=9 July 2020 |archive-date=11 July 2020 |archive-url=https://web.archive.org/web/20200711122417/https://www.antiquewireless.org/wp-content/uploads/50-the_first_wireless_time_signals_to_ships_at_sea.pdf |url-status=live }}</ref>

[[Radio navigation]] systems came into general use after [[World War II]]. The systems all depended on transmissions from fixed navigational beacons. A ship-board receiver calculated the vessel's position from these transmissions.<ref name="Pierce">{{cite journal |last1=Pierce |first1=J.A. |s2cid=20739091 |title=An introduction to Loran |journal=Proceedings of the IRE |date=1946 |volume=34 |issue=5 |pages=216–234 |doi=10.1109/JRPROC.1946.234564}}</ref> They allowed accurate navigation when poor visibility prevented astronomical observations, and became the established method for commercial shipping until replaced by [[Global Positioning System|GPS]] in the early 1990s.