On this day in 1861, the One O'clock Gun fired for the first time. In 1852, the time ball was erected on top of the Nelson Monument on Calton Hill. It was designed as an optical time signal for ships in the Firth of Forth. The drop of the ball allowed ship’s captains to synchronise their chronometers to ensure accurate navigation at sea. But the notorious haar – a cold sea fog that covers Edinburgh for days at a time – made this an unreliable means of time-keeping. The idea of an audible signal

Edinburgh Castle Cannon : The medieval Mons Meg a massive siege gun, and the modern one O’clock Gun, a 105mm field gun fired daily as a time signal. | Senen Fortin

On this day in 1861, after two previous failed attempts, the One o’clock Gun fired successfully. The One O’clock Gun is one of only a few surviving time signals, once a common feature of ports around the United Kingdom. Its sound was intended to replicate a visual time signal, given by a falling ‘time ball’ on the top of Nelson’s Column on Carlton Hill, which was installed in 1852 . The precise timing of the ball’s fall allowed ships’ captains to set their chronometers accurately. This enabled t