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The Clock Tower is a turret clock structure at the north-eastern end of the Houses of Parliament building. It is colloquially known as Big Ben, however this name actually belongs to the clock's main bell. The tower was raised as a part of Charles Barry's design of a new palace, after the old Palace of Westminster was destroyed by fire on October 16, 1834.
The tower is designed in the Victorian Gothic style, and is 96.3m (316') high. The first 61m (200') of the structure is the clock tower, consisting of brickwork with stone cladding; the remainder is a framed spire of cast iron. The tower is founded on a 15m x 15m (49' x 49') raft, made of 3m (9') thick concrete, at a depth of 7m (23') below ground level. The tower has an estimated weight of 8,667 tonnes (9,553 tons). Due to ground conditions, the actually tower leans slightly to the north-west, by roughly 220mm (8.66").
The four clock faces are 55m (180') above ground. They were once large enough to allow the Clock Tower to be the largest four-faced clock in the world, but has since been outdone by the Allen-Bradley Clock Tower in Milwaukee, Wisconsin. The Great Clock of Westminster still holds the title of the "World's largest four-faced chiming clock", though. The hour hand is 9' long and the minute hand is 14' long. The clock faces and dials were designed by Augustus Pugin. The faces are set in an iron framework 7m (21') in diameter supporting 576 pieces of opal glass. The surround of the dials is heavily gilded. At the base of each clock face in gilt letters is the Latin inscription 'DOMINE SALVAM FAC REGINAM NOSTRAM VICTORIAM PRIMAM' meaning 'Lord save our Queen Victoria I'. The clock mechanism itself was completed by 1854, but the tower was not fully constructed until four years later in 1858. The clock became operational on September 7, 1859.
Big Ben, officially known as the Great Bell of Westminster, is the largest bell in the tower. Cast in 1856 in Stockton-on-Tees by George Meers, it cracked under the striking hammer while mounted in New Palace Yard. It was recast at Whitechapel Bell Foundry as the the 12.5 tonne (13.8 ton) bell which is in use today. Installed into the clock tower in 1908, another crack formed. To prevent further damage to the bell it was rotated and the main hammer was reduced in weight. The origin of the name 'Big Ben' has remained a popular mystery, leading to speculation it was named after heavyweight boxer Benjamin Caunt. A more populate alternate theory says it was named after Sir Benjamin Hall, who was the Parliamentary Commissioner of Works. The BBC first broadcast the "E" note chimes on December 31, 1923.
Along with the main bell, the belfry houses four quarter bells which play the Westminster Quarters on the quarter hours. The four quarter bells are G sharp, F sharp, E, and B. They play a 20 chime sequence, 1-4 at quarter past, 5-12 at half past, 13-20,1-4 at quarter to, and 5-20 on the hour. Because the low bell (B) is struck twice in quick succession, there is not enough time to pull a hammer back, and it is supplied with two hammers on opposite sides.
The clock is famous for its reliability, due in large part to the experimentation by designer, lawyer and amateur horologist Edmund Beckett Denison, later Lord Grimthorpe. As the clock mechanism, created to Denison's specification by clockmaker Edward John Dent, was completed before the tower itself, Denison ditched the original deadbeat escapement and remontoire, and invented the double three-legged gravity escapement. This provides the best separation between pendulum and clock mechanism. Together with an enclosed, wind-proof box sunk beneath the clockroom, the Great Clock's pendulum is well isolated from external factors like snow, ice and pigeons on the clock hands, and keeps remarkably accurate time.
Despite heavy bombing the clock ran accurately throughout the Blitz. It slowed down on New Year's Eve 1962 due to heavy snow, causing it to chime in the new year 10 minutes late. The clock had its first and only major breakdown in 1976 when the chiming mechanism broke due to metal fatigue, and was reactivated again on in 1977. In May 2005 it stalled ticking for two separate 90 minute stints.