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A bridge in London's Docklands
Standing on prime meridian in Greenwich
websize photograph
Description of the photograph
Title: Shepherd gate 24-hour clock
Taken from:

At the Royal Greenwich Observatory, London, England.


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 analogue dial.

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.

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 and 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.

By 1866, time signals were being sent to Harvard University via transatlantic cable.

The Gate Clock originally indicated astronomical time, in which the counting of the 24 hours of each day starts at noon. The clock was changed in the 20th century to indicate Greenwich Mean Time, in which the counting of the 24 hours of each day starts at midnight. Currently, the Gate Clock continues to show Greenwich Mean Time, and it does not show daylight saving time. The clock is now controlled by a quartz mechanism inside the main building. The master clocks are still on display, but are not functional.

Keywords: wall, gate, brick, clock
Image data
Image sizes: 1024*1500px, 980kb
Origin: Scanned from analog paper print
Date/Time: 19970508-170000
Destination coordinates;WGS84 LONG -0.00151544809341°, LAT 51.477821472°, coordinates may be inaccurate!
Author: Alexandra Medwedeff
Photo copyright: This photograph is copyrighted (©) by André M. Winter and others. A free permissions for re-use may be given for non-commercial purposes. Commercial use requires a license. Contact André M. Winter for any kind of use. This extended copyright notice applies in all cases. Infringements always will be persecuted worldwide. Legal court: Innsbruck, Austria, E.U.
Text copyright: The description of this photograph (or parts of) is based on this article of the free Wikipedia encyclopedia and are covered by the GNU Free Documentation License (GFDL). Authors are named on the Wikipedia page.
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