Big Ben and the Great Clock of Westminster
Strictly speaking, Big Ben is a bell of about 13.7 tonnes. The clock below it and the tower around it have stories just as dramatic.
Bell, clock or tower?
People point at the tower in Westminster and call it Big Ben, but the name properly belongs to the largest bell inside it. The machine that drives the dials is officially the Great Clock, and the tower itself was long known as the Clock Tower or St. Stephen's Tower.
In 2012 it was renamed Elizabeth Tower to mark Queen Elizabeth II's Diamond Jubilee. Parliament's fact sheet gives its height as over 96 meters, with 334 steps up to the belfry.
The bell's nickname is usually said to honor Sir Benjamin Hall, the commissioner of works at the time. Parliament calls him the probable source, and Britannica says only that some historians hold this view, so it remains a likely story rather than a proven one.
A clock that had to be right to the second
The old Palace of Westminster burned down in 1834, and the rebuilt palace needed a clock tower. The architect, Charles Barry, turned to clock experts for advice, and the commission became a long tug-of-war among them.
The Astronomer Royal, George Airy, set a demanding target: the first stroke of each hour should be accurate to within one second. At the time, Parliament notes, local time could vary by about 15 minutes from one part of Britain to another.
A competition was held in 1846. Edmund Beckett Denison, a lawyer and gifted amateur horologist, drew up the winning designs, which were judged ready in February 1852. The chronometer maker Edward John Dent was hired to build the clock. Dent died before it was finished, and Frederick Dent, described by the Linda Hall Library as his adopted son, took over.
Parliament says the mechanism took two years to build and dates its completion to 1854, at a cost of 2,500 pounds. The tower was not ready for it until 1859, when the clock was finally installed.
Even the start date is disputed. Parliament says the clock began keeping time on 31 May 1859, while the Linda Hall Library gives an inauguration date of 1 May 1859. To prove its accuracy, it was checked against time signals sent by telegraph from the Royal Observatory at Greenwich.
See also: when the UK clocks change on OnlineClock.app.
Denison's escapement and the famous pennies
The real breakthrough was in the escapement, the part that lets the gear train advance in steady steps. Denison invented the double three-legged gravity escapement in 1854. It both regulates the pendulum and keeps it swinging, and it was a late change: Denison swapped it in, almost at the last minute, for the design he and Airy had agreed.
The design was soon widely copied in tower clocks. Denison did not bother to patent it.
Fine-tuning is famously low-tech. A stack of old pennies sits on the pendulum. According to Parliament, adding one penny makes the clock gain about two-fifths of a second over 24 hours. The pendulum is 4.4 meters long and weighs 310 kilograms.
Everything about the machine is heavy. Parliament gives the pendulum bob alone as 203 kilograms, the three driving weights as nearly 2.5 tonnes together, and the clock mechanism as about 5 tonnes. Denison later became the first Baron Grimthorpe, in 1886, which is why his invention is also called the Grimthorpe escapement.
The bell that cracked twice
The first Great Bell was cast in August 1856 at John Warner's foundry near Stockton-on-Tees. During testing in 1857 it developed a crack 1.2 meters long. The founder and the clock's designer argued over who was to blame, and the bell was broken up.
A replacement was cast at the Whitechapel Bell Foundry by George Mears in 1858 and hauled to the tower by horses. The new bell first rang on 11 July 1859, and within months it cracked as well. Denison blamed the foundry, which sued him for libel, according to Britannica; the case was settled out of court.
Rather than recast the bell again, Airy proposed a fix. The bell was turned so the hammer struck a fresh spot, a lighter hammer was fitted, and the crack was cut to stop it spreading.
Sources differ on when the bell returned to service: Britannica says 1862, Parliament says 1863. Its weight is also given two ways. Parliament's fact sheet and Britannica say 13.7 tonnes, while another Parliament page gives 13.5 tonnes.
The Great Bell is 2.7 meters across and sounds an E. Four smaller quarter bells, each weighing 1 to 4 tonnes, ring the Westminster Chimes around it every 15 minutes.
See also: Westminster and other clock chimes on OnlineClock.app.
The dials and hands
Each of the four dials is 7 meters across, framed in cast iron and glazed with 312 separate pieces of opal glass. Their centers are 55 meters above the ground, which explains why everything has to be so big to look normal from the street.
The hour hands are gunmetal and 2.7 meters long. The minute hands are copper sheet and 4.2 meters long, and Parliament calculates that each minute hand travels about 190 kilometers a year.
Above the belfry, another 59 steps continue to the Ayrton Light, the lantern at the top of the tower that was added in 1885. The hammer that strikes the Great Bell weighs 200 kilograms.
The 2017-2022 restoration
On 21 August 2017 the bell fell mostly silent for a restoration that Britannica describes as a four-year project. It ran longer than that: Parliament's 2022 progress report expected the work to finish that October.
During the works the bell still sounded for special occasions such as New Year's Eve and Remembrance Sunday, while the clock mechanism was taken down for repair.
The Victorian mechanism was reinstalled in 2022 after what Parliament called the most intensive conservation in the clock's history, and the dials were due to get new energy-efficient LED lighting. The machine keeping time today is still, essentially, the one Denison and the Dents built.
Questions people ask
Is Big Ben the tower or the bell?
The bell. The tower is Elizabeth Tower, renamed in 2012, and the timekeeping machine is called the Great Clock.
How do they keep Big Ben on time?
By adding or removing old pennies on the pendulum. According to Parliament, one penny makes the clock gain about two-fifths of a second a day.
Why is the bell called Big Ben?
It is most often said to be named after Sir Benjamin Hall, the commissioner of works when it was installed, but this has never been conclusively proven.
When did the clock start?
Parliament gives 31 May 1859 as the day the clock began keeping time, though the Linda Hall Library says 1 May. The bell first rang on 11 July 1859.