struck in a different place. Big Ben has chimed with a slightly different tone ever since, and is still in use today with the crack unrepaired. Big Ben was the largest bell in the British Isles until "Great Paul", a 16.75-ton (17 tonne) bell currently hung in St Paul's Cathedral, was cast in 1881. In August 2007, the bell's striker was replaced for the first time since installation. Nickname The origin of the nickname Big Ben is the subject of some debate. The nickname was applied first to the Great Bell; it may have been named after Sir Benjamin Hall, who oversaw the installation of the Great Bell, or after English heavyweight boxing champion Benjamin Caunt. Now Big Ben is often used, by extension, to refer to the clock, the tower and the bell collectively, although the nickname is not universally accepted as referring to the clock and tower. Some authors of works about the tower, clock and bell sidestep the issue by using the words Big Ben first in the title, then going on to clarify that the subject of the book is the clock and tower as well as the bell. Chimes Along with the Great Bell, the belfry houses four quarter bells which play the Westminster Quarters on the quarter hours. The four quarter bells sound G, F, E, and B. They were cast by John Warner & Sons at their Crescent Foundry in 1857 (G, F and B) and 1858 (E). The Foundry was in Jewin Crescent, in what is now known as The Barbican, in the City of London. The bells are sounded by hammers pulled by cables coming from the link room—a low-ceiling space between the clock room and the belfry—where they are triggered by cables coming from the chime train. The quarter bells play a once-repeating, 20-note sequence of rounds and four changes in the key of E major: 1–4 at quarter past, 5–12 at half past, 13–20 and 1–4 at quarter to, and 5–20 on the hour (which sounds 25 seconds before the main bell tolls the hour). Because the low bell (B) is struck twice in quick succession, there is not enough time to pull a hammer back, and it is supplied with two wrench hammers on opposite sides of the bell. The tune is that of the Cambridge Chimes, first used for the chimes of Great St Mary's church, Cambridge,