Building the Great Clock's mechanism

Charles Barry was a fine architect but he was not a specialist clockmaker. He sought advice from a friend, Benjamin Lewis Vulliamy, after adding a prominent clock tower to his design for rebuilding Parliament after the 1834 fire.

Vulliamy was the Queen's Clockmaker. He began designing a clock for Barry's tower. Other respected clockmakers, like Edward John Dent, wanted to be involved and disputes broke out. In 1846 a competition was held to decide who should build the clock.

The Astronomer Royal, Sir George Airy, was appointed referee and set out high standards for the clock to meet. These included:

  • the first stroke of each hour to be accurate to within one second
  • the clock's performance to be telegraphed twice a day to Greenwich Observatory

Seven years delay

Airy's demanding standards led to delays which lasted seven years. During this time Airy appointed Edmund Beckett Denison to support him in his decision. Denison was a barrister and also a gifted amateur clockmaker.

In February 1852, Dent was appointed to build the clock to Denison's own design.

The next delay occurred when it was discovered space inside the tower was too small for the planned clock design. Modifications costing £100 had to be made.

Dent died in 1853 and his stepson, Frederick, completed the clock in 1854. It cost £2500 to make.

There was another delay because the Clock Tower wasn't finished on schedule. Until installation in 1859, the clock was kept at Dent's factory. Denison made many refinements including inventing the 'Double Three-legged Gravity Escapement'. This was a revolutionary mechanism, ensuring the clock's accuracy by making sure its pendulum was unaffected by external factors, such as wind pressure on the clock's hands.

Denison's invention has since been used in clocks all over the world. It is also known as the 'Grimthorpe Escapement' as Denison was made Baron Grimthorpe in 1886.

The clock was installed in the Clock Tower in April 1859. At first, it wouldn't work as the cast-iron minute hands were too heavy. Once they were replaced by lighter copper hands, it successfully began keeping time on 31 May 1859. It was not long before the chimes of the Great Bell, also known as Big Ben, joined in.

Find out more about Big Ben and the Elizabeth Tower


You can access biographies of

Charles Barry
Edward John Dent
George Airy
Edmund Beckett Denison

from the Oxford Dictionary of National Biography for free, online, using your local library card number (includes nine out of ten public libraries in the UK) or from within academic library and other subscribing networks.