The World's Oldest Working Clock

When they weren't drinking mead, toiling in the fields or dying from the bubonic plague, the people of 14th century England were going to church. A lot. That's why the oldest working clock in Europe, and quite possibly the world, can be found in an English cathedral, and was built as a means to (loudly) remind the locals that one of the day's seven or eight church services were about to start. More than 600 years later, that very same clock is faithfully "ticking" away, its large, iron cogs slowly rotating as a small shaft clinks into a metal cog every four seconds.

The clock, which is located in Salisbury Cathedral in southern England, was commissioned by Bishop Erghum and dates from about 1386. There was apparently a mechanical clock already working in Milan, Italy, by 1335, but the Salisbury clock is the oldest of its kind known to still be working.

With its massive iron wheels and long ropes reaching halfway up the cathedral walls, it looks more like an industrial-age engine than the clocks we know today. But it did the trick, chiming a bell on the hour, for 24 hours a day. The word "clock" comes from the same root as glocke, the German word for bell, since the earliest clocks were meant to be listened to, not "watched." The clocks of medieval times were probably grossly inaccurate, but that didn't really matter.

"In those days people didn't need to know if it was four minutes to 11," said Dudley Heather, head of guides at Salisbury Cathedral. "They just needed to know when it was time to go to church, or perhaps to eat." Mechanical clocks like the one in Salisbury Cathedral came to fundamentally change the way time was measured. Before it, only astronomers divided a day into 24 hours, while everyone else gave the periods of day and night 12 "temporal hours," the length of which varied throughout the year.

The clocks of ancient times relied on some sort of repetitive process: the rising and setting of the sun for sundials, and water dripping from a hole at the bottom of a stone vessel with water clocks, which were used as far back as 1500 B.C.

But the Salisbury clock was an example of how clock makers had shifted from the continuous flow of things like water and sand, to measuring small increments of time. It works via a system of weights and pulleys. Two long ropes are wound up a couple of spools, or barrels, and each is then threaded through a pulley about 20 feet above the clock. At the bottom end of each rope is a weight, originally made from lead, now stone. Each rope is fully wound back around the barrels every morning, pulling the weights to the top. As the day wears on, they slowly sink back down to the floor.

Key to everything is the "verge and foliot," a clever mechanism right inside the clock that maintains the weights' slow descent and the keeping of time. It is essentially two small weights on either side of a small, horizontal beam that is suspended by a thread, called the foliot. The weighted beam is pushed back and forth while a vertical rod in the middle of the beam, the verge, then catches against the "teeth" of a rotating wheel every four seconds, with a sonorous "clink." While one of the barrels drives the verge and foliot, the other, rarely used today, controls the hourly striking of the bell.

The invention of the verge and foliot was critical in the development of time keeping. It was the first mechanism that used repetition to keep the time, and paved the way for pendulum clocks. Previously, people had relied on the flow of water, as with water clocks, and it's probable that the three makers of the Salisbury clock used either a water clock or sundial to calibrate their device.

Centuries after its creation, the Salisbury clock was replaced by a more modern device that chimed quarterly, and it was tucked away into the cathedral's bell tower. When in 1930 a curious horologist noticed its dusty old iron framework, he immediately suspected its historical importance.

Today the clock has been refurbished to its former glory, with only a few small parts replaced in the 1950s by Derbyshire clock makers. To save it from any extra wear and tear, it no longer chimes, save for the odd demonstration to clock enthusiasts a few times a year.

While Salisbury Cathedral doesn't know how much Bishop Erghum paid for his clock, it was probably quite a lot. Clocks in these days were made from iron or brass, which were expensive metals, and these sorts of clocks took months, perhaps even years, to build. The whole community was expected to chip in for the town clock since it would help everyone organize their daily routines.

The Bishop, no doubt eager to get the newest technology for the Cathedral, probably had to pass a basket or two around to get enough donations from his parishioners. If they had grumbled about it at the time, the locals would almost certainly have been impressed when the clock was finally in full, working order, faithfully chiming out the hours. And they would have been simply amazed if they could have known that their Cathedral clock would still be up and running centuries later.

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