Somewhere above the Palace of Westminster, a clockmaker occasionally climbs the 334 spiral steps of the Elizabeth Tower, opens the case of a swinging pendulum, and places an old pre-decimal penny on a small tray fixed to its shaft. That single coin will make the most famous clock in the world run about two-fifths of a second a day faster. Take a penny off and it slows by the same amount. The physics is elegant: the coin does not add meaningful weight so much as shift the pendulum's centre of mass fractionally upwards, shortening its effective length and quickening its beat. A Victorian mechanism the size of a small room is trimmed to modern accuracy with pocket change — and has been since 1859.
The clock exists because of a catastrophe. In October 1834 the medieval Palace of Westminster burned down, and the replacement designed by Charles Barry and Augustus Pugin included a great clock tower. The Astronomer Royal, George Airy, set the specification: the first strike of each hour was to be accurate to within one second, with the clock's performance telegraphed twice a day to Greenwich for checking. Respectable clockmakers protested that no large public clock, its hands dragged at by wind, rain and snow, could possibly meet such a standard. The man who proved them wrong was not a clockmaker at all but a barrister — Edmund Beckett Denison, a brilliant, combative amateur horologist later ennobled as Lord Grimthorpe. His double three-legged gravity escapement isolated the pendulum from whatever the weather was doing to the hands outside, delivering an identical tiny push with every swing. The design became standard in great tower clocks worldwide, and Denison pointedly never patented it. Built by the clockmaker Edward John Dent and finished by his stepson Frederick after his death, the Great Clock began keeping time on 31 May 1859.
A bell that broke twice
The bells were less obliging. The first Great Bell, cast in 1856 at Warner's foundry, cracked beyond repair in 1857 while being tested — Denison, characteristically sure of himself, had insisted on a heavier hammer than the founders advised. The replacement was cast in April 1858 by the Whitechapel Bell Foundry, the same house that had cast Philadelphia's Liberty Bell; at 13.7 tonnes it was hauled across Westminster Bridge on a carriage drawn by sixteen horses, cheered through the streets. It first sounded in July 1859 — and by September it too had cracked. Rather than recast it again, the engineers turned the bell a quarter of a turn so the hammer struck clear of the fissure, fitted a lighter hammer, and cut a small square notch to stop the crack spreading. That crack is still there, and it is why Big Ben's E-natural strike has its slightly imperfect, instantly recognisable voice.
Strictly, "Big Ben" is the bell alone — not the clock, and not the tower, a distinction quizmasters adore. The tower was officially the Clock Tower until 2012, when it was renamed the Elizabeth Tower for the Queen's Diamond Jubilee. Even the nickname's origin is disputed: the leading theory honours Sir Benjamin Hall, the imposingly large commissioner of works whose name is inscribed on the bell, while a rival tradition credits Benjamin Caunt, a celebrated heavyweight prize-fighter of the day. The record does not settle the question, which rather suits the bell's mythology.
Keeping time through everything
The Great Clock's reliability became part of the national self-image. The BBC first broadcast its chimes to the country at midnight on New Year's Eve 1923, and the "bongs" went on to open news bulletins through the darkest years of the century. In May 1941 a German air raid destroyed the Commons chamber below and scarred the tower's stonework, yet the clock neither stopped nor lost its rate. Beneath each of the four opal-glass dials runs a gilded Latin inscription — Domine salvam fac Reginam nostram Victoriam Primam: "O Lord, keep safe our Queen Victoria the First." Between 2017 and 2022 the tower underwent its largest-ever conservation: the mechanism was dismantled piece by piece for restoration, and the bell fell largely silent, sounding only for occasions such as New Year and Remembrance Sunday — a hush that itself made front pages.
Through all of it, the tuning method has never changed. The clock is still wound by hand three times a week; the keepers still check its rate against Airy's astonishing Victorian target; and when it drifts, nobody reaches for electronics. They reach for a penny. In an age that measures time by the vibrations of caesium atoms, Britain's national timekeeper is regulated with small change — which may be the most quietly confident piece of engineering in London.
Quiz nuggets
- Adding one old penny to the pendulum tray speeds the Great Clock by about two-fifths of a second per day.
- Big Ben is strictly the 13.7-tonne Great Bell; the tower, called the Clock Tower until 2012, is now the Elizabeth Tower.
- Barrister Edmund Beckett Denison's double three-legged gravity escapement met Astronomer Royal George Airy's one-second accuracy standard from 1859.
- The Whitechapel-cast bell cracked in 1859; it was turned a quarter of a turn and given a lighter hammer, and the crack gives its distinctive tone.
- The nickname's origin is disputed between Sir Benjamin Hall, commissioner of works, and the prize-fighter Benjamin Caunt.