May 31: On This Day in 1859 - London's Big Ben

May 31, 1859: London's Big Ben officially started keeping time on this day. Big Ben is the world's largest four-faced chiming clock and stands 314-feet high. Big Ben's chime is based on four notes from Handel's Messiah and rings every fifteen minutes. Although most people refer to the entire tower as the Big Ben Clock Tower, the name Big Ben actually refers to the bell housed within the tower. The bell itself weighs almost 14 tons, and takes its name from the man who first ordered the bell, Sir Benjamin Hall.

The clock faces are set in an iron frame 7metres (23ft) in diameter, supporting 312 pieces of opal glass. At the base of each clock face in gilt letters is the Latin inscription DOMINE SALVAM FAC REGINAM NOSTRAM VICTORIAM PRIMAM, which means O Lord, keep safe our Queen Victoria the First.

On August, 5, 1976, there was the first and only major breakdown. The speed regulator of the chiming mechanism finally broke after 100+ years of torsional fatigue, then the fully-wound 4 ton weights dumped their entire potential energy into the chiming mechanism in one go. It caused a great deal of damage; the Great Clock was shut down for a total of 26 days over nine months - it was reactivated on 9 May 1977; this was its longest break in operation since it was built.

On June 5, 2006, the clock tower's "Quarter Bells" were taken out of commission for four weeks because a bearing holding one of the quarter bells was damaged from years of wear and needed to be removed for repairs. And on August 11, 2007, it was stopped for 6-weeks of maintenance, so the bearings in the clock's drive train and the "great bell" striker were replaced for the first time since installation