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
Liverpool ObservatoryWaterloo Dock
John Hartnup the Director 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.
It is thought that not more than three of these clocks were made. It kept sidereal time, that is, time according to the stars rather than the sun. The clock is driven by weights in the usual manner and has a normal pendulum. However, a peculiar feature is that the clock movement terminates in a frictionally driven wheel carrying an arm, which comes to rest on a pallet. In this position the driving wheel continues to run freely and does not affect the driven wheel, as this has part of its circumference cut away. The pendulum releases the pallet and the arm of the driven wheel falls under gravity, breaking the electrical circuit used to operate a chronograph. The movement is then taken up again by the driving wheel, and so on. One special feature is the great rapidity with which the electrical circuit is broken and re-made. Another is that the impulses to the pendulum are less frequent - once in two seconds - than with normal clocks. Yet another unusual feature is that the pendulum is not used to operate electrical contacts. The rotating pendulum at the top of the clock stores energy in order to make the contacts. In 1856 the Magnetic Telegraph Company laid down wires from the Observatory clock to the clock in the Exchange Buildings.
The sidereal clock
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