Northumbrian Gunner: Edinburgh - One O Clock Gun Exhibition Edinburh Castle

The chronometer was the primary mechanism for measuring longitude and relied on ships instruments being set accurately. The problem of measuring longitude was solved by John Harrison who developed clocks and watches to measure time accurately on board ship, and was successfully trailed by Captain James Cook in 1776.

To set their chronometers, ships captains would need to leave their ships and set the time by refrence to master clocks maintained for that purpose in ports.The One O Clock time signal was instituted to allow ships captains to set their chronometers without leaving their ships.One O clock was selected as the time for the signal as it allowed readings to be taken at mid day.

The first time signal was instituted at Portsmouth in 1829 and consisted of a ball dropped from a mast. In 1833, a time ball was set up at the Greenwich Observatory. The East India Company decided to set time balls up along their trade routes, leading to the mechanism being adopted around the world. A further development was the introduction of guns being fired to signal the time.

The time ball in Edinburgh was set up on the Nelson Memorial on Carlton Hill in 1853. An electric signal from the adjacent observatory triggered the ball being dropped. Unfortunately the signal was difficult to spot in foggy weather. In 1858 it was therefore proposed that a gun be fired on Carlton Hill to signal one o clock. There was concern the gun firing would disturb the instruments, so it was decided to fire the gun from Edinburgh Castle. A 4,000 feet (1,220 metres) wire connected the time ball on Cartlon Hill to the gun on the Half Moon Battery.

The first firing occurred 7th June 1861.

One O Clock Gun fired from Half Moon Battery

Although the gun would fire at precisely One O Clock, the sound would take a number of seconds to travel, consequently to set time accurately it would be necessary to know the exact time the noise of the firing was heard. This lead to the publishing of Sound Maps for Edinburgh.

In 1863 the observatory was connected to time guns in Newcastle and South Shields.

The first One O Clock Gun was a 12 pounder muzzle loader, which was replaced by a 18 pounder muzzle loader in September 1861. In 1913 a 32 pounder Dwarf Gun was used, which would be replaced in July 1923 by an 18 pounder QF Gun. In 1952 a 25 pounder became the One O Clock Gun.