Big Ben is the nickname for the great bell of the clock at the north end of the Palace of Westminster in London, and often extended to refer to the clock and the clock tower. The tower is now officially called the Elizabeth Tower, after being renamed in 2012 (from "Clock Tower") to celebrate the Diamond Jubilee of Elizabeth II. The tower holds the largest four-faced chiming clock in the world and is the third-tallest free-standing clock tower. The tower was completed in 1858 and had its 150th anniversary on 31 May 2009, during which celebratory events took place.[5][6] The tower has become one of the most prominent symbols of both London and England and is often in the establishing shot of films set in the city.
The clock's movement is famous for its reliability. The designers were the lawyer and amateur horologist Edmund Beckett Denison, and George Airy, the Astronomer Royal. Construction was entrusted to clockmaker Edward John Dent; after his death in 1853 his stepson Frederick Dent completed the work, in 1854. As the tower was not complete until 1859, Denison had time to experiment: Instead of using the deadbeat escapement and remontoire as originally designed, Denison invented the double three-legged gravity escapement. This escapement provides the best separation between pendulum
and clock mechanism. The pendulum is installed within an enclosed
windproof box sunk beneath the clockroom. It is 13 feet (4.0 m) long,
weighs 660 pounds (300 kg) and beats every 2 seconds. The clockwork
mechanism in a room below weighs 5 tons. On top of the pendulum is a
small stack of old penny coins; these are to adjust the time of the clock. Adding a coin has the effect of minutely lifting the position of the pendulum's centre of mass,
reducing the effective length of the pendulum rod and hence increasing
the rate at which the pendulum swings. Adding or removing a penny will
change the clock's speed by 0.4 seconds per day.[
On 10 May 1941, a German bombing raid damaged two of the clock's
dials and sections of the tower's stepped roof and destroyed the House of Commons chamber. Architect Sir Giles Gilbert Scott
designed a new five-floor block. Two floors are occupied by the current
chamber, which was used for the first time on 26 October 1950. Despite
the heavy bombing the clock ran accurately and chimed throughout the Blitz.
The clock tower tilts as a result of the excavation of tunnels near Westminster. The tower has tilted an additional 0.9 mm each year since 2003, and the tilt can now be seen by the naked eye.
Malfunctions, breakdowns, and other interruptions in operation
- 1916: for two years during World War I, the bells were silenced and the clock face darkened at night to prevent attack by German Zeppelins.
- 1 September 1939: although the bells continued to ring, the clock faces were darkened at night through World War II to prevent guiding Blitz pilots.
- 1949: The clock slowed by four and a half minutes after a flock of starlings perched on the minute hand.
- New Year's Eve 1962: The clock slowed due to heavy snow and ice on the long hands, causing the pendulum to detach from the clockwork, as it is designed to do in such circumstances, to avoid serious damage elsewhere in the mechanism – the pendulum continuing to swing freely. Thus it chimed in the new year 10 minutes late.
- 5 August 1976: First and only major breakdown. The air brake speed regulator of the chiming mechanism broke after more than 100 years of torsional fatigue, causing the fully wound 4-ton weight to spin the winding drum out of the movement, causing a large amount of damage. The Great Clock was shut down for a total of 26 days over nine months – it was reactivated on 9 May 1977; this was its longest break in operation since its construction. During this time BBC Radio 4 had to make do with the pips. Although there were minor stoppages from 1977 to 2002 when the maintenance of the clock was carried out by the old firm of clockmakers Thwaites & Reed, these were often repaired within the permitted two hour downtime and not recorded as stoppages. Prior to 1970 maintenance was carried out by the original firm of Dents and since 2002 by Parliamentary staff.
- 27 May 2005: the clock stopped at 10:07 p.m. local time, possibly because of hot weather; temperatures in London had reached an unseasonable 31.8 °C (90 °F). It resumed, but stopped again at 10:20 p.m. local time and remained still for about 90 minutes before resuming.
- 29 October 2005: the mechanism was stopped for about 33 hours so the clock and its chimes could be worked on. It was the lengthiest maintenance shutdown in 22 years.
- 7:00 a.m. 5 June 2006: The clock tower's "Quarter Bells" were taken out of commission for four weeks as a bearing holding one of the quarter bells was damaged from years of wear and needed to be removed for repairs. During this period, BBC Radio 4 broadcast recordings of British bird song followed by the pips in place of the usual chimes.
- 11 August 2007: Start of 6-week stoppage for maintenance. Bearings in the clock's going train and the "great bell" striker were replaced, for the first time since installation. During the maintenance works, the clock was not driven by the original mechanism, but by an electric motor. Once again, BBC Radio 4 had to make do with the pips during this time.
- 17 April 2013: The bells were silenced as a mark of "profound dignity and deep respect" during the funeral of Margaret Thatcher.
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