The Shepherd Gate Clock was installed at the gates to the Observatory, and was the first clock ever to show Greenwich Mean Time (GMT) directly to the public.
The first thing you notice about the Gate clock is that it has 24 hours on its face rather than the usual 12. That means at 12 noon the hour hand is pointing straight down rather than straight up.
But this clock is not just an Observatory novelty.
The Shepherd Gate Clock is known as a 'slave' clock, because it depends on another clock inside the main Observatory building for its accuracy: the Shepherd Master Clock.
While the Shepherd Gate Clock is the one most visitors see, the Master Clock is the true technological breakthrough.
Its time was sent via telegraph wires to London, Edinburgh, Glasgow, Dublin, Belfast and many other cities. By 1866, time signals were even sent from this clock to Harvard University in Massachusetts via the new transatlantic submarine cable.
In terms of the distribution of accurate time into everyday life, this is one of the most important clocks ever made.
Why is it called the 'Shepherd' clock?
In 1851 at the famous Great Exhibition held in Hyde Park, London, one of the world's first ever 'master-and-slave' clock systems was installed by Charles Shepherd of Leadenhall Street.
It consisted of a central 'master clock' sending regular electrical impulses to a number of connected 'slave' dials.
George Airy, the seventh Astronomer Royal, saw the potential advantages of such a system and ordered one to be made for the Royal Observatory in Greenwich.
The Shepherd system was supplied to Greenwich Observatory the following year and remained the basis of Britain’s time-distribution system for the next 70 years. Both the Shepherd Gate Clock and the Shepherd Master Clock are named after their inventor.
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