Greenwich

Charles II founded the Royal Observatory by royal warrant in 1675, so that the tables of the Moon and stars could be made exact enough to find a ship’s longitude at sea.^1, 2, 6

The dates are recorded closely: on 4 March 1675 the King named John Flamsteed his astronomical observator, on 22 June he ordered a small observatory at Greenwich, on 10 August Flamsteed laid the foundation stone, and on 10 July 1676 he moved in. Christopher Wren designed the building, with Robert Hooke assisting.^1, 6, 7

The new Observatory drew on London’s clockmakers from the start: Thomas Tompion made its clocks in 1676, and Jonas Moore, who paid for instruments himself, gave two of them for the Octagon Room.^6, 9, 10

The connection lasted: George Graham, Tompion’s successor in Fleet Street, built Halley’s mural quadrant at Greenwich and the zenith sector Bradley used.^11, 12

Royal Museums Greenwich dates the Admiralty’s takeover of the Observatory, and its role as the Royal Navy’s chronometer testing centre, to 1821, with John Pond as Superintendent of Chronometers; Wikipedia’s history of the Observatory gives 1818 for the move from the Board of Ordnance to the Admiralty.^1, 2, 6

The Admiralty bought chronometers on the results of yearly trials at Greenwich. Jenny Bulstrode and Andrew Meek date these premium trials from 1822 and say they ended in 1836, when Airy succeeded Pond; Wikipedia’s account of the marine chronometer puts the start of the Greenwich competition in 1820.^13, 14

A chronometer could win its career at Greenwich: Thomas Porthouse’s No. 233, on trial from 1823 to 1825, was bought by the Navy at once and served for 112 years.¹⁵

Airy made the trials harder. Bulstrode and Meek record that soon after succeeding Pond he asked the Hydrographer, Francis Beaufort, whether chronometers could be tried at extremes of temperature, then tested them out of doors, in the chronometer room and before a fire. Wikipedia dates Airy’s trials from 1840 to 1914.^13, 14

In 1833 Pond put a time ball on the roof of Flamsteed House. Each day it rises halfway at 12.55, reaches the top at 12.58 and drops at 1 pm exactly, a signal for mariners on the Thames and anyone else watching.^{1, 16, 17}

In 1852 an electric system by Charles Shepherd of Leadenhall Street, who had shown a master clock driving several dials at the Great Exhibition, linked the Observatory’s clock to a 24-hour dial at the gate, a clock at London Bridge station, the time ball and a ball on the Strand, and sent signals along the railways out of London.^1, 4

From January 1851 Airy’s transit circle defined the Greenwich meridian; Royal Museums Greenwich says it made about 600,000 observations in more than a century of use.^6, 20

From May 1766 Maskelyne kept Harrison’s H4 at the Observatory for ten months of trial; it did not perform well, and the quarrel over the longitude prize deepened.^21, 22

London’s chronometer makers sent their work to Greenwich to be rated: Edward John Dent’s glass-spring chronometers were rated there from 1833, and Thomas Mercer, who set up in Clerkenwell in 1858, sent chronometers to the Greenwich trials.^13, 23

Greenwich time travelled by rail: the Railway Clearing House recommended it for all stations in September 1847, and by 1855 time signals from Greenwich could be sent along railway lines across Britain.^4, 24

In October 1884 an International Meridian Conference in Washington, called by President Chester A. Arthur, resolved to propose to governments the meridian through the transit instrument at Greenwich as the initial meridian for longitude.^3, 25

The case for Greenwich was practical. Sandford Fleming, a British delegate, put before the conference figures showing Greenwich used by 65 per cent of the world’s ships and 72 per cent of its tonnage; Royal Museums Greenwich says nearly two-thirds of ships already used charts based on it.^3, 20

Greenwich time became the law of Great Britain by the Statutes (Definition of Time) Act of 2 August 1880.^1, 24

The 1884 conference also proposed a universal day, a mean solar day beginning at mean midnight on the Greenwich meridian, which was not to interfere with local or standard time. Royal Museums Greenwich says it recommended a world system of time zones based on Greenwich Mean Time; the conference’s Final Act contains no resolution on zones.^3, 20

The astronomers then left Greenwich, though the dates differ: Royal Museums Greenwich’s history of the site has departments moving to Herstmonceux Castle in Sussex from 1948, its research guide gives 1958, and Wikipedia says the move begun in 1948 was completed in 1957. The Royal Greenwich Observatory moved to Cambridge in 1990 and closed in 1998.^1, 2, 6

The buildings became a museum: the National Maritime Museum opened beside them on 27 April 1937, Royal Museums Greenwich dates the Observatory site’s transfer to it to 1953, and Flamsteed House opened to the public in 1960.^1, 27

Rupert Gould restored Harrison’s four timekeepers between 1923 and 1939, and the Royal Observatory is where they are usually shown.^28, 29

Since 1997 the Observatory has been part of the Maritime Greenwich World Heritage Site. The zero of longitude itself has moved on: Royal Museums Greenwich notes that the International Reference Meridian of today’s satellite systems lies 102.5 metres east of Airy’s line.^20, 31