Westminster’s chiming clock


Tucked away at the north-eastern end of London’s Houses of Parliament is that ultimate British icon — Westminster’s Great Clock Tower. The name of “Big Ben” for the tower is a misnomer. That is the moniker of the principal Great Bell within the Tower.

The tower started life as part of Charles Barry’s Victorian Gothic design for a new Palace of Westminster in the 1830s. The clock itself was ready by 1854 but the Tower was not completed until 1858, with the clock — and its chimes — becoming operational on September 7, 1859.

The 96.3 m tower is set upon a 15 x 15m, 3m thick, concrete raft, poured 7m below ground level. The first 61m of the Tower consists of brickwork clad with stone. The remainder is a framed spire of cast iron. Due to ground movements the Tower now leans about 220mm from the vertical up at the clock face.

The clock faces are set 55m up and are the design of Augustus Pugin. Each dial is set in a 7m diameter iron framework, and contains 312 pieces of opaline glass. The hour hand is 2.7m long and the minute hand 4.3m.

The surrounds are heavily gilded as is the inscription across the base of each face: DOMINE SALVAM FAC REGINAM NOSTRAM VICTORIAM PRIMAM (May the Lord keep safe our Queen Victoria the First).

The clock’s precision is a tribute to the genius of its designer, lawyer and amateur horologist Edmund Denison, later Lord Grimthorpe.
He invented the double three-legged gravity escapement used for this clock. This mechanism effectively separates clock mechanism from the pendulum that is enclosed in a wind-proof box beneath the clock room.

As such, it is isolated from the weather — and pigeons — and is, hence, able to keep remarkably accurate time, although a particularly heavy snow fall on December 31, 1962, caused it to slow and chime-in the New Year 10 minutes late.

The clock’s pendulum is traditionally tuned by adding or subtracting old-style pennies to a stack borne on the pendulum. The addition or removal of a single penny changes the clock’s speed by 2/5ths of a second per day.

Big Ben was the informal name given to a 14.5 tonne hour bell cast in April 1856. However, it cracked when struck while awaiting installation and was recast as the present 13.76 tonne, 2.2m high, 2.9m diameter bell. This main bell strikes A and hangs alongside four quarter-hour bells that play G sharp, F sharp, E and B, in a 20 chime sequence.


• Westminster’s Great Clock is the world’s largest four-faced chiming clock, but is exceeded in size by Milwaukee’s non-chiming Allen-Bradley Clock Tower.
• The chimes of Big Ben broadcast on the BBC are transmitted live via a microphone permanently installed in the tower, a practice that began in 1923.

• On August 11, 2007, the bells were silenced to allow a full month’s overhaul and the clock was driven by an electric motor, with the BBC having to make do with time pips.
• The clock suffered its only major breakdown in 1976 when the chiming mechanism broke due to metal fatigue.

• German bombing in WWII damaged two of the clock faces and the tower’s steepled roof, but the clock continued to keep excellent time.
• The clock stopped in April 1997 and May 2005, but in October 2005 it was deliberately decommissioned for 30 hours to allow the chimes to be serviced.

• The Westminster clock face in the opening titles of ITV News is computer-generated.
• A terrorist manual found in the home of Abu Hamza al-Masri in 2005 marked Big Ben for demolition, along with the Statue of Liberty and the Eiffel Tower.

Science is fun!

A person standing at the base of the clock tower hears Big Ben chime approximately 1/6th of a second after the bell is struck.
In contrast, a person listening to the BBC’s World Service in, say, the United States would hear the same bell chime live via the microphone placed in the tower well before the person on the ground.

If the BBC listener was to immediately re-transmit the chime back to the ground-based observer via, say, a satellite telephone, the bell chime would still be heard on the phone before the direct sound reached the ground observer.

The direct sound takes 0.16 seconds to reach the ground but a radio signal can get to New York and back in less than 0.04 seconds given that the speed of light (= radio waves) is considerably greater than the speed of sound.

The Clock Tower has starred in:

• The Thirty Nine Steps
• V for Vendetta when it explodes

• Peter Pan
• 101 Dalmatians

• Independence Day 
• Mars Attacks!

• The War of the Worlds
• The Simpsons

• Inspector Gadget
• Doctor Who — many times, including being
   destroyed at least once

• The Prisoner
• Captain Scarlet
• And, of course, in Thunderball  Ernst Blofeld instructs MI6 to have Big Ben ring seven times a six o’clock to show agreement with SPECTRE’s terms.

Try it using your cell phone the next time you are in London!