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. Technically, Big Ben is the name given to the massive bell inside the clock tower, which weighs more than 13 tons (13,760 kg).
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.
The bottom 200 feet (61.0 m) of the tower’s structure consists of brickwork with sand colored Anston limestone cladding.
The remainder of the tower’s height is a framed spire of cast iron. The tower is founded on a 50 feet (15.2 m) square raft, made of 10 feet (3.0 m) thick concrete, at a depth of 13 feet (4.0 m) below ground level.
The four clock dials are 180 feet (54.9 m) above ground. 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 clock’s time is adjusted every year with an old British penny. If the clock is fast, a penny is added to the pendulum, and if the clock is slow, one is removed.
The Clock Tower is also known as Big Ben Tower, and is sometimes erroneously referred to as St. Stephen’s Tower. St Stephen’s Tower is actually found in the center of the west side of the Houses of Parliament, and acts as the public entrance.
It is not open to the general public or foreign visitors. Only UK residents are allowed to climb Big Ben and tours needs to be pre-arranged a tour through your MP or a Lord.
Due to changes in ground conditions since construction, the tower leans slightly to the north-west, by roughly 230 millimeters (9.1 in) over 55 m height, giving an inclination of approximately 1/240. This includes a planned maximum of 22 mm increased tilt due to tunneling for the Jubilee line extension.
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. So, whenever you happen to take a trip to London, make sure to visit Big Ben, the world’s largest clock.