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The College clock is housed in one of the oldest buildings in Trinity: King Edward’s Gate, otherwise known simply as the clock-tower. This gate originally formed a grand entrance to King’s Hall, a foundation which was dissolved in 1546 and joined with Michaelhouse to found the new College of the Holy and Undivided Trinity. As part of the building works initiated under the Mastership of Thomas Nevile, this gate was taken down stone-by-stone and rebuilt 100 feet or so north of its original location, thereby helping to create Great Court on its current expansive scale.
A clock, dial-plate, and bell seems first to have been added to the clock-tower in 1610 by one Thomas Tennant, a citizen of London. The bell is still in place, and in use, and bears the inscription:


(The Trinity resounds in unity. 1610.
Richard Holdfield [or Oldfield] made me.)

A new clock and dial-plate were put in place under the Mastership of Richard Bentley, in 1726–27. The original “1610” clock mechanism was given to the village of Orwell. It still runs today in the tower of the village church. Meanwhile in Trinity two new bells were provided for the chimes before the striking and the wooden bell-tower on top of the gate was modified from the original one constructed in 1610. This wooden tower was replaced by a replica in 1856–57.

In 1910 the old clock was replaced yet again by the mechanism which is still now in place. It was built by Smith of Derby to a design by Lord Grimthorpe very much along the lines of the mechanism used for the clock in the Palace of Westminster (“Big Ben”). The clock is governed by a temperature-compensated pendulum 2 metres in length driven by a three-legged gravity escapement. It is a remarkable instrument, capable of keeping time to better than one second in a month without any intervention.

Since it was replaced in the early eighteenth century, the Trinity clock has been notable for striking the hour twice, first on a low note (the ‘Trinity’ chime) and then on a much higher one (the ‘St John’s’ chime). This phenomenon was recorded by William Wordsworth in his poem ‘The Prelude’ (1850):

Near me hung Trinity’s loquacious clock,
Who never let the quarters, night or day,
Slip by him unproclaimed, and told the hours
Twice over with a male and female voice.

The running of the 1910 clock has been the the subject of an engineering project coordinated by a Fellow of Trinity, Dr Hugh Hunt, calibrating the clock’s movements against the National Physical Laboratory time signal and various variables, including the amplitude of the pendulum, humidity, air temperature, air pressure, and air density.

For more information and research regarding the clock, visit the Trinity College Clock project

You can also read a short piece in The Conversation by Hugh about the accuracy on the clock.

Monitoring Project - Escapement

The escapement is the key part of a clock that connects the train of gears to the pendulum. Working together, the pendulum and escapement define the accuracy of a clock’s timekeeping and it is Denison’s double three-legged gravity escapement which was finally fitted to the Great Clock that produced an exceptionally accurate clock. In simple terms, Denison’s escapement along with a compensation pendulum, produced a clock that kept time to within a few seconds a week. In horological terms Denison’s escapement was one of the most significant inventions of the 19th century. In a subtle way it supported the growing need for accurate public timekeeping as society relied more on railways for communication. From the 1860s onwards many thousands of turret clocks were made and installed in factories, churches, town halls, hospitals, prisons, workhouses etc. Many of these clocks had a gravity escapement; the economic boom fuelled the turret clockmaking industry and the clocks installed brought order and timekeeping and thus fuelled social and economic progress”.

“What Denison’s gravity escapement did was to always provide a constant impulse to the pendulum irrespective of weather conditions, so the pendulum arc remained the same hence timekeeping was constant. This was achieved by raising a small weighted arm that was then ‘lowered’ onto the pendulum to give it a push or impulse. Since the arm was a constant weight and always descended the same distance under the influence of gravity, the impulse given to the pendulum was constant. In fact two arms were used, one on each side of the pendulum”

It is remarkably accurate, known to be better than one second per month. In 2009 a system was installed to monitor the “going”. The work was done as part of a 4th year MEng project at the Engineering Department. A sensor on the pendulum detects the going of the clock, which is compared to the accurate time signal from a GPS receiver. For an entirely mechanical clock the accuracy is remarkable. Follow @clockkeeper on twitter.

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