Why does Big Ben bong on the radio before it does in real life?

The debate over whether Big Ben should bong to mark Brexit isn’t the first time the famous bell has caused consternation. Listeners to a BBC radio news bulletin in 1949 were horrified when the chimes failed to sound. They had to wait until a later bulletin for an explanation: the clock was running four minutes slow because a swarm of starlings had gathered on the minute hand.

In fact, right from the start there were problems with the Great Bell. (That’s its official name — ‘Big Ben’ is a nickname honouring, depending on who you believe, either Sir Benjamin Hall, who oversaw its installation, or Benjamin Caunt, a heavyweight boxer.) The original bell, cast in Stockton-on-Tees, cracked during tests in New Palace Yard. A replacement was made at the Whitechapel Bell Foundry, and carried to Westminster through cheering crowds on a trolley drawn by 16 horses. It began striking on 11 July 1859, but within two months it too had developed a crack. A lighter hammer was installed (even this one weighs a fifth of a ton), and the bell was turned slightly so the strike occurred in a different place. The crack is there to this day.

Big Ben’s note is an E (though changes in official concert pitch since the 19th century make it closer to a modern F). Four smaller bells play the tune just before the hour is struck. One of these (the B note) is needed twice in quick succession, meaning the hammer doesn’t have time to reset, so there’s another hammer on the opposite side. The tune has words: ‘All through this hour, Lord be my Guide. And by thy power, no foot shall slide.’

Do book yourself in for a tour of the Elizabeth Tower when they restart after the current renovation works are completed. You get to stand just a few feet from Big Ben as it rings out, so make sure you do the tour that finishes at midday — more bong for your buck, or rather for your no buck, as the tours are free. You can also see the microphone that carries the sound to the BBC for its live transmissions (though of course at the moment it is using a recording).

The fact that Auntie broadcasts the bongs live was of crucial importance in a 1967 episode of Captain Scarlet. In ‘Big Ben Strikes Again’, the puppet hero had to find a location where someone had reported hearing the clock strike 13. His colleague Captain Blue realised that this let them compute the distance from parliament — the delayed sound waves from the bell must have been striking exactly in sync with the bongs as heard on the radio. So the 13th bong was simply a ‘real’ repeat of the 12th one already heard over the airwaves.

The discrepancy arises because radio waves travel at the speed of light rather than the speed of sound (186,000 miles per second versus 760 miles per hour). So you should also, when live transmissions resume, perform the delightful experiment of standing at the bottom of the Elizabeth Tower (on the pavement opposite Westminster Tube), listening to the bongs on Radio 4 (analogue rather than digital — the latter is slightly delayed). You hear Big Ben on the radio before you hear it for real. Sounds impossible, but I’ve tried it, and I promise you it’s true.