Big Ben starts keeping time

Background. The Great Clock of Westminster is housed in the Clock Tower, now known as the Elizabeth Tower, at the north end of the Palace of Westminster in London. The tower was designed by Augustus Pugin and Sir Charles Barry in the Perpendicular Gothic style. The clock mechanism was designed by Edmund Beckett Denison and George Airy, the Astronomer Royal, and constructed by Edward John Dent and Frederick Dent.

Construction. The clock mechanism was built by Edward John Dent to designs by Edmund Beckett Denison. Denison invented a double three-legged gravity escapement, which provided better separation between the pendulum and clock mechanism, mitigating weather effects. The tower was completed in 1859, and the clock entered service in that year, striking the hour to within a second of the time.

The Great Bell. The main bell, officially known as the Great Bell but popularly called Big Ben, is the largest bell in the tower. It was recast on 10 April 1858 at the Whitechapel Bell Foundry as a 13.5-ton bell. This new bell first chimed on 11 July 1859, but cracked under the hammer in September of that year.