Liverpool Observatory was built at Waterloo Dock, Liverpool in 1845 and one of its objectives was to establish Greenwich time and to indicate it each day to the citizens of the Port of Liverpool. Eventually many towns and cities developed their own time ball systems, but it was particularly important for maritime ports to have a precise time signal. Chronometers on board ship had to be exact in order for the ships position to be accurately known.
John Hartnup at the Liverpool Observatory determined sidereal time from the stars by means of the transit telescope situated in one of the domes on the Observatory roof. A sidereal clock at the Observatory kept sidereal time, and solar time was calculated from it. A time ball was fitted to the outside wall of the Observatory and was dropped each day at exactly one o'clock so that the citizens and mariners could check their timepieces. A time ball is a sphere, which slides up and down a vertical mast and can be abruptly dropped at an appointed hour. It was similar in all respects to that used at Greenwich and also at Portsmouth, which were also dropped at one o'clock.
In 1856 the Magnetic Telegraph Company laid down wires from the Observatory clock to the clock in the Exchange Buildings. This clock was a Henley's Electro-magnetic clock, which had a large dial, which was easily seen from Exchange Flags. The second hands of the Observatory and Henley's clocks moved simultaneously, being connected electrically. This service was not only for chronometer makers and owners, but also for the general public. In 1857 the Town Hall clock, approximately a mile from the Observatory was also connected to the Observatory. In 1860 the clock in Victoria Tower, which had six dials eight feet in diameter, was also connected to the system. A time ball was fitted to this clock and was visible from the river. Chronometer makers and mariners could be seen assembling around the both points in Liverpool to check their instruments as the time balls fell at exactly one o'clock. As a further service to mariners the staff of Liverpool Observatory also rated and checked ships' chronometers over various temperatures.
When the dock was redeveloped, a new Observatory was built on the top of Bidston Hill
in Wirral in 1866, some three miles across the River Mersey. Accurate time still needed to be indicated to the people of Liverpool, but, due to the distance of the new Observatory, it now had to be with the aid of an audible signal. The staff continued to observe the passage of the stars with the aid of the transit telescope, which was situated, in the eastern dome of the Observatory, thus determining time.
A cannon at Morpeth Dock, Birkenhead was fired remotely from Bidston Observatory at one o'clock each working day, triggered electrically by a specially adapted Robert Molyneux clock. On the dockside, the cannon, a relic of the Crimean wars, was loaded, and at 12.30pm each working day a member of staff tested the connection between the clock at the Observatory and the cannon. At one second to one o'clock the switch would be thrown at the Observatory, the firing being triggered by the next swing of the clock's pendulum. On clear days the flash could be spotted from across the Mersey.
This service was performed from 1867 until July 18th 1969, apart from a break during the Second World War. An extra firing heralded the start of the 20th century. An attempt was made to scrap the time signal in 1932, partly because it was no longer necessary, due to the advent of radio, but also because of the cost of maintenance of the gun, said to be approximately one hundred pounds a year. There was a public outcry at the prospect of the ending of this tradition, so the War Office provided a new cannon, a 32 pounder from Woolwich Arsenal, which arrived on April 26th 1933. The old cannon was on display in the grounds of Bidston Observatory for many years.
In 1946, after a wartime silence of six and a half years, this cannon was then replaced by a third gun, a six pounder naval anti-aircraft Hotchkiss gun, and on June 17th the old familiar sound once more reverberated across the River Mersey.
In 1969 Bidston Observatory became a component body of the Natural Environment Research Council, concentrating on oceanographic research, and it was decided to discontinue the tradition of firing the One O'clock Gun on the grounds of efficiency.
One of the earlier cannons is now at the Maritime Museum, Liverpool. The transit telescope is now in the Liverpool Museum. The clock used for the firing of the One O'Clock Gun remains on display at the Observatory (now known as the Proudman Oceanographic Laboratory).