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Encyclopedia > Shepherd gate clock
Shepherd Gate Clock at Royal Greenwich Observatory
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Shepherd Gate Clock at Royal Greenwich Observatory

The Shepherd Gate Clock is the clock mounted on the wall outside the gate of the Royal Greenwich Observatory building in Greenwich, London. The clock, an early example of an electric clock, was a slave mechanism controlled by electric pulses transmitted by a master clock inside the main building. The 'network' of master and slave clocks was constructed and installed by Charles Shepherd in 1852. The clock by the gate was probably the first to display Greenwich Mean Time to the public, and is unusual in using the 24 hour analog dial. Royal Observatory, Greenwich The original site of the Royal Greenwich Observatory (RGO), which was built as a workplace for the Astronomer Royal, was on a hill in Greenwich Park in Greenwich, London, overlooking the River Thames. ... Greenwich (pronounced grenn-itch , or by the locals) is a town, now part of the south eastern urban sprawl of London, on the south bank of the River Thames in the London Borough of Greenwich. ... London (pronounced ) is the capital city of England and the United Kingdom. ... An electric clock is a clock that is powered by electrical current instead of powered by springs or weights. ... a cheap Vostok 24 hour watch reading 09:54 The clock at Ottery St Mary. ...

Contents

Origins

The original idea for the clock network came from the Astronomer Royal, George Airy. With the arrival of the railway network, a single time standard was needed to replace the various incompatible local times then in use across the country. Airy proposed that this standard time would be provided by the Royal Observatory. His idea was to use what he called 'galvanism' or electric signalling to transmit time pulses from Greenwich to slave clocks throughout the country, and perhaps to Europe and the colonies too. The new undersea cable recently installed between Dover to Calais in 1851 raised the possibility of sending time signals between England and France - this would allow longitude differences to be measured very accurately, for the first time. George Biddell Airy Sir George Biddell Airy (July 27, 1801 – January 2, 1892) was British Astronomer Royal from 1835 to 1881. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Location within France The Burghers of Calais, by Rodin, with Calais Hotel de Ville behind J.M.W. Turner: Calais Pier Calais (Dutch: ) is a town in northern France, located at 50°57N 1°52E. It is in the département of Pas-de-Calais, of which it is a...


Charles Shepherd

In 1849, Charles Shepherd, of 53 Leadenhall Street, London, had patented a system for controlling a network of master and slave clocks using electricity (or galvanism, as it was called). Shepherd, an engineer and son of a clockmaker, had installed the public clocks for the Great Exhibition which opened in May 1851. In October, Airy wrote to Charles Shepherd asking for proposals and estimates, including a request for the following clocks: The Great Exhibition: Paxtons Crystal Palace enclosed full-grown trees in Hyde Park. ...

One automatic clock. One clock with large dial to be seen by the Public, near the Observatory entrance, and three smaller clocks, all to be moved sympathetically with the automatic clock.

Airy also wanted the existing Greenwich time ball to be electrically operated, so that its descent at 13:00 was synchronized with the master clock inside the observatory. The timeball at Greenwich is shown in the top right of picture A time ball is a large metal or painted wooden ball, visible to shipping, that drops at a predetermined time to enable sailors to set their chronometers. ...


By August 1852, Shepherd had built and installed the network of clocks and cables in the observatory. Costs were considerably higher than the original estimates. Shepherd had estimated £40 for the master clock and time ball apparatus, and £9 for each sympathetic clock. The total costs included £70 for the master clock, and £75 for the wall clock by the gate.


Transmitting Greenwich time

By August 1852, Shepherd's clock system was 'up and running'. The master clock, at first called the Normal Clock or Master Clock, but later known as the Mean Solar Standard Clock, sent pulses every second to the sympathetic or slave clocks in the Chronometer Room, the Dwelling House (Flamsteed House), and to the Gate Clock. A pulse was also sent to the time ball at 13:00. The signals were also transmitted along cables from Greenwich to London Bridge. At London Bridge, a time signal was distributed at less frequent intervals to clocks and receivers throughout England.


Airy's report to the Observatory's Board of Visitors in 1853 explained the function of the Shepherd master clock:

This clock keeps in motion a sympathetic galvanic clock in the Chronometer room, which, therefore, is sensibly correct; and thus the chronometers are compared with a clock which requires no numerical correction. The same Normal Clock maintains in sympathetic movement the large clock at the entrance-gate, two other clocks in the Observatory, and a clock at the London Bridge Terminus of the South-Eastern Railway. It sends galvanic signals every day along all the principal railways diverging from London. It drops the Greenwich Ball and the Ball on the Offices of the Eastern Telegraph Company in the Strand. All these various effects are produced without sensible error of time; and I cannot but feel a satisfaction in thinking that the Royal Observatory is thus quietly contributing to the punctuality of business through a large portion of this busy country.

By 1866, time signals were being sent to Harvard University via transatlantic cable. Harvard University (incorporated as The President and Fellows of Harvard College) is a private university in Cambridge, Massachusetts. ...


The Gate Clock originally indicated astronomical time, in which the counting of the 24 hours of a day starts at noon every day rather than midnight. In the 20th century, the clock was changed to show Greenwich Mean Time, which it still does - it doesn't show daylight savings time. The clock is now controlled by a quartz mechanism inside the main building, and the master clocks are still on display, but not working. Daylight saving time (also called DST, or Summer Time) is the local time a region is designated for a portion of the year, usually an hour forward from its standard official time. ...


See also

Royal Greenwich Observatory Royal Observatory, Greenwich The original site of the Royal Greenwich Observatory (RGO), which was built as a workplace for the Astronomer Royal, was on a hill in Greenwich Park in Greenwich, London, overlooking the River Thames. ...


References

  • Howse, Derek Greenwich Time and the Longitude 1997, Oxford University Press

External links

  • National Maritime Museum
  • Shepherd clock screensaver a software emulation running as a MacOS X screensaver

 
 

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