The maritime masterpiece crafted in 1727 by the Yorkshire clockmaker John Harrison was accurate to within a minute a week and could help sailors calculate longitude and thus measure their distance from land.
Its intricate, wooden mechanism still works perfectly – but in what might be seen as a timely warning about pale imitations, a faithful copy designed to show Harrison’s workings to the world has stopped dead.
The two clocks are displayed next to each other near the entrance to Leeds City Museum, with the reproduction, which dates only from the 1970s, stripped of its face and cabinet.
Matthew Read, an expert in antique clocks, arrived yesterday to try to fathom why its works had ground to a halt.
“We’ll be investigating whether it’s dirty or if it needs some added lubrication,” he said.
Harrison’s original “longcase clock No 2” is credited with helping to solve the problem of accurate timekeeping on lengthy voyages. It led him to produce a mariners’ watch that could accurately maintain time at sea.
Valued at around £2m, it was bequeathed to the city of Leeds by a local resident, William Wyrill Sissons, in 1973, in a transaction whose paperwork is lost. No-one is sure whether he knew of its value or significance.
At around the same time as his largesse was recorded, an enthusiast was crafting a cog-for-cog reproduction of the clock, using the same self-lubricating African hardwood favoured by Harrison. It is on loan to Leeds from the National Maritime Museum at Greenwich.
“There’s a real, palpable sense of history when you look at these things,” said Mr Read, director of the Bowes Centre for Art, Craft and Design at Barnard Castle. “The original clock that Leeds owns is in incredibly good condition, and looking inside gives you a direct connection with the past.”
The 1727 clock, which the museum has wound down to prevent wear and tear, was designed in the wake of a disaster in which four cargo ships sailing from Gibraltar to England and commanded by the Admiral of the Fleet, Sir Cloudesley Shovell, ran aground in the Scilly Isles, having mistaken their position. The miscalculation cost 2,000 lives.
The government set up the Longitude Board, and offered £20,000 to anyone who could come up with a way of measuring a ship’s position at sea.
Harrison became obsessed with the challenge, and set about making a high-precision clock that would keep time despite changes in weather and the motion of the waves.
A Yorkshire joiner with little access to scientific equipment, he overcame the problems of heat and humidity that affected the accuracy of timekeeping by keeping clocks in different rooms of his cottage, building up the fire in one while leaving the other cold. The project took him 50 years to complete.
In 1772, Captain James Cook tested the device on his second and third voyages of discovery, reporting on his return that he had been won over by “our never-failing friend”.
Harrison was born at Foulby on the Nostell Priory Estate near Wakefield. The family moved to Barrow-on-Humber, and John followed his father into joinery.
But he was no ordinary craftsman. He became a self-taught scientist, mathematician and engineer with a particular passion for timepieces, which he made his life’s work.
He was awarded the Longitude Prize by King George III, a fan of technology and horology, who had the clocks tested in his own observatory.
Harrison was 80 when the accolade finally came, and died three years later.