The time of day

From where I’m sitting, I can see several clocks — on my desk, mantelpiece, computer, phone and watch, but I never truly appreciated them until I read LONGITUDE by Dava Sobel (and enjoyed the film, starring Jeremy Irons and Dumble Michael Gambon). Back in the 1700s, no sooner had sailors ventured out of sight of land than they lost all way of knowing their longitude (east-west position). Hence countless ships ran onto rocks and unexpected shores, or drifted past island havens into barren seas.

In 1714, the English Parliament offered a then-massive financial reward (£20,000) for a reliable and practical way of measuring longitude.

The scientists of the time believed the answer lay in astronomy; centuries had already been devoted to mapping the stars and in the mid 1700s this was still being investigated, not least by the fifth Astronomer Royal, The Reverend Dr Nevil Maskelyne. However, lunar measurements required hours of calculations and even at best, the measurements were out by miles.

John Harrison sought a mechanical solution instead: the marine chronometer — which meant building an unfailingly accurate clock that could withstand the movement of a rolling ship and the extremes of temperature from tropics to northern climes. It took decades, resulting in a series of trips across the Atlantic to test out his various chronometers, and battling negative feedback from Nevil Maskelyne (who seemed to have no qualms about conflicts of interest) along the way.

Four chronometers stand in the Royal Observatory today, three protoypes ticking away, and the fourth, the final one, lies still (due to its delicacy).

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H1: Harrison’s first marine chronometer.

The early chronometers stand over a foot tall, gimballed and armed with bimetallic strips, they account for nautical rolls and pitches and changes in temperature, adjusted here and there over the years with as much intricacy as a skeleton and its ligaments. But while they held the time well, they were expensive and impractical to make on a commercial scale. It was only the production of a much smaller model, barely bigger than a pocket watch, that would be commercially viable enough for Harrison (now an old man after a lifetime’s work) to receive his prize.

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H4: Harrison’s last chronometer was a more practical size, and considered commercially viable.

While Harrison laboured over his clocks, Nevil Maskelyne worked on star maps, charting positions and setting up algorithms and charts to reduce the extensive calculations as much as possible, yet still running up against the limitations of solar angles.

His book is still available, The British Mariner’s Guide. Containing, Complete and Easy Instructions for the Discovery of the Longitude at Sea and Land.

These men dedicated their lives to bringing us the accurate timepieces we enjoy today.

Fling your veg: