Clock[edit]
Dials[edit]
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Augustus Pugin drew inspiration from the clockmaker Benjamin Lewis Vulliamy when he designed the dials. Each is made of cast iron sections bolted together. The whole frame is 22.5 feet (6.9 m) in diameter making them the third largest in the UK. They each contain 324 pieces of opalescent glass.[33] Originally, the dials were backlit using gas lamps, at first only when Parliament was sitting, but they have routinely been illuminated from dusk until dawn since 1876. Electric bulbs were installed at the beginning of the 20th century.[34] The ornate surrounds of the dials are gilded. At the base of each dial is the Latin inscription DOMINE SALVAM FAC REGINAM NOSTRAM VICTORIAM PRIMAM, which means "O Lord, keep safe our Queen Victoria the First".[35] Unlike many Roman numeral clock dials, which show the "4" position as IIII, the Great Clock faces depict "4" as IV.[36] The clock's gun metal hour hands and copper minute hands are 8.75 feet (2.7 m) and 14 feet (4.3 m) long respectively.[37]
When completed, the frame and hands were Prussian blue, but were painted black in the 1930s to disguise the effects of air pollution. The original colour scheme was reinstated during the 2017–2021 conservation work. It was found that no fewer than six different colour schemes had been used over the past 160 years.[38] The Victorian glass was also removed and replaced with faithful reproductions made in Germany by glassmakers Glasfabrik Lamberts.[39]
Movement[edit]
The clock's movement is known 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.[40] As the tower was not completed until 1859, Denison had time to experiment: instead of using a deadbeat escapement and remontoire as originally designed, he invented a double three-legged gravity escapement, which provides the best separation between pendulum and clock mechanism, thus mitigating the effects of rain, wind and snow on the dials.[41] Dent never patented his design, and it quickly became the standard on all new high-quality tower clocks.[42]
On top of the pendulum is a small stack of pre-decimal 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.[43] It keeps time to within a few seconds per week.[44] It is hand wound (taking about 1.5 hours) three times a week. The Keeper of the Clock is responsible for looking after the movement in addition to overseeing every aspect of maintenance around the Palace. A team of horologists are on call 24 hours a day to attend to the clock in the event of an emergency.[45]
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. The clock ran accurately and chimed throughout the Blitz.[46]