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First electric GMT clock

The dial set into the wall outside the gate to the Royal Observatory, Greenwich in south-east London isn't really a clock at all, in the normal sense. It is just one of five slave dials reliant on timing signals, or electrical impulses, received from the Master clock inside. Another slave on the same Master clock system is located at London Bridge rail station.

It was the first clock dial to publicly display Greenwich Mean Time and was constructed by Charles Shepherd of 53 Leadenhall Street, London in August 1852 on the instructions of the Astronomer Royal, George Airy.

Airy had seen the system demonstrated at the Great Exhibition in Hyde Park the previous year. Despite labelling himself as the patentee, Shepherd was in constant battle with Alexander Bain, a Scot, who claimed an earlier patent.

The 920mm dial is split into 24 hours instead of 12 so the hour hand rotates once a day. 24 hour dials aren't uncommon but here the hour hand points to the bottom rather than the top at midday, and that is unusual.

The minute and seconds hands still rotate the conventional once each hour/minute respectively. Note that it also follows clock traditions of using IIII for the Roman number 4 although the reason is less convincing here (IIII is traditionally used on clocks in place of the more 'correct' IV to help give a dial some balance against the VIII opposite - but note an important exception: Big Ben).

For the next forty years the Shepherd master clock time was sent by telegraph to London, Edinburgh, Glasgow, Dublin, Belfast and many other cities.

By 1866, time signals were sent from the clock to Harvard University in Cambridge, Massachusetts via the new transatlantic submarine cable. In terms of the distribution of accurate time into everyday life, it is therefore one of the most important clocks ever made and worthy of its inclusion in this series of short articles.

It also operates the red 'time' ball on the roof of the Observatory at Flamsteed House which rises every day at 12.55pm, taking three minutes to reach the top where it stops, falling at exactly 1pm to enable passing ships to set their clocks. Whilst noon might have been thought of as a more appropriate time, it is said that astronomers were too busy with their telescopes at midday.

In this age of satellite navigation, the tradition is now continued mainly for the benefit of tourists.

Greenwich of course became the 'home' of time in the UK when King Charles II established the first zero Meridian by ordering the construction of an observatory in 1675 in the Royal Park. Other countries followed.

As recently as 1850 people were still following local time, which varied across Britain by half an hour East to West, so travellers frequently had to adjust their watches when they arrived at their destination. The development of the railway created a need to 'standardise' time across the country and GMT was finally adopted in 1880 for the UK.

But the existence of countless more zero meridians around the world made international navigation and chart-making ever more complicated so on 1 October 1884 delegates met at the International Meridian conference in Washington to agree on a world's zero meridian. They inevitably chose Greenwich because pioneering navigators such as James Cook already had charts centred on Greenwich and the British made charts and Nautical almanac were the leaders of their type.

The 24 local time zones were developed from that.

Click here to read more about the final clock in this series of articles, BIG BEN.


  • The clock (actually a slave dial) at Shepherd Gate, Greenwich
  • Master clock at Greenwich
  • The red ball at Flamstead House, Greenwich
  • The Zero Meridian line at Greenwich
  • Exploting the Greenwich Meridian