Big ben

Big Ben is the nickname for the great bell of the clock at the north end of the Palace of Westminster in London,[1] and is generally extended to refer to the clock or the clock tower as well. Some believe this extension to be incorrect, but its usage is now entirely commonplace.[2] It is the largest four-faced chiming clock and the third-tallest free-standing clock tower in the world.[3] Itcelebrated its 150th anniversary in May 2009,[4] during which celebratory events took place.[5][6] The clock was finished being built on April 10, 1858.
The bottom 61 metres (200 ft) of the Clock Tower's structure consists of brickwork with sand coloured Anston limestone cladding. The remainder of the tower's height is a framed spire of cast iron. The tower is founded on a 15-metre (49 ft) squareraft, made of 3-metre (9.8 ft) thick concrete, at a depth of 4 metres (13 ft) below ground level. The four clock dials are 55 metres (180 ft) above ground. The interior volume of the tower is 4,650 cubic metres (164,200 cubic feet).
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.[12] 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 separationbetween pendulum and clock mechanism. The pendulum is installed within an enclosed windproof box sunk beneath the clockroom. It is 3.9m long, weighs 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 theposition 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.[6]
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. ArchitectSir 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.
Big Ben es el nombre con que se conoce a la Gran campana de Westminster, la mayor de las campanas que se encuentran en la Torre del Reloj que forman parte delGran Reloj de Westminster del Palacio de Westminster, ubicado en la ciudad Londres. Aunque este nombre le corresponde a la gran campana, popularmente también se le aplica a la Torre del Reloj en su conjunto. La torre se encuentra en la esquina noroeste del edificio que alberga la sede de las dos Cámaras del Parlamento Británico. El Big Ben fue construido en el año 1858.
Malfunctions, breakdowns,and other outages

The south clock face being cleaned on 11 August 2007
* 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.[8]
* Sept. 1, 1939: although the bells continued to ring, the clock faces were darkened at night through World War II to prevent guiding Blitz pilots.[8]
* New Year's Eve1962: 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.[13]
* 5 August 1976: First and only major breakdown. The air brake speed regulator of...