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09 April 2013

Dava Sobel: Longitude

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In this day-and-age we take global positioning for granted - I even have a GPS system on my smartphone. But for hundreds of years mariners sailed the globe without knowing exactly where they were. They could easily check their latitude through the sun and stars but had virtually no idea of where they were because they couldn't easily work out their longitude. Intrepid explorers like Vasco da Gama, Ferdinand Magellan, and Sir Francis Drake virtually sailed willy nilly about the globe following a known latitude, using dead reckoning and hoping that by good luck and judgement that they would arrive at their destination. Many missed their way and perished, others wandered way off course with the risk that the crew would die of scurvy.

Dava Sobel has written an easy-reading popular account of endeavours during the 18th Century to find an accurate and easy way to measure longitude in a marine environment. She sets out a general history of one of the greatest competitions in history when the Longitude Act of 1714 offered a major prize (equivalent to several million dollars now) for the first person to accurately solve the longitude problem.

Basically there were 2 competing methods, an accurate timepiece or finding position from observation of the heavens. The competition was full of challenge, amazing achievement and skulduggery and dirty deeds. Accurate time at sea was especially challenging with changing temperatures and intense movement of the ship. Using the heavens required detailed mathematics to convert the sightings with cloud cover giving only intermittent access to the heavens for guidance.

The story is really about the competition between a mechanical genius, John Harrison, who spent his lifetime constructing complex sea-clocks (chronometers)and his nemesis Nevil Maskelyne, a supporter of the observational approach, who did everything he could to prevent Harrison's clocks winning the competition.

The outcome was a world where mariners could plot their position with accuracy in any weather anywhere in the world. This fuelled world trade and population movements during the years of the first Industrial Revolution when Britain most definitely "ruled the waves".

I am a fan of easy reading history and I recommend this to anyone who wants to learn about the drama and skills behind one of greatest advances in technology in the 18th century. I kept my rating to 4 stars because I read it in Kindle version and missed the illustrations of Harrison's clocks that feature prominently in the print version. Thank goodness that Google's image search was able to show me the complexity and beauty of Harrison's work.


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