London Greenwich - Shepherd Clock on meridian line

Postcard

 

• Picture / Image:  Shepherd Clock - 24 hour public clock at the Royal Greenwich Observatory installed in 1852
• Publisher:  National Maritime Museum, 2005
• Postally used:  no
• Stamp:  n/a
• Postmark(s):  n/a
• Sent to:  n/a
• Notes & Key words: 

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Text from the free encyclopedia WIKIPEDIA may appear below to give a little background information:

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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.

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:

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.

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.