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    'Sextant' by David Barrie
    From: Michael Bradley
    Date: 2014 Jul 13, 04:16 -0700

    An interesting, lively, well written, and  apparently well researched read this one, written from a West European point of view. It includes chapters on the experiences and adventures of Cook, Bligh, Anson, Bougainville, La Perouse, Finders, Worsley and the likes. The classical astronomers and almanac compilers who followed Copernicus are mentioned. There is a slightly grudging short piece on Sumner. Polynesian methods are described briefly, but with credible detail. Most chapters start with a short written passage of the author's personal reminiscences from sailing non stop across the North Atlantic in a wooden yacht, three up, learning astro on the way.

    The book fills out some of the answers to the Lunar/Chronometer crossover question: there are several mentions describing the the use of a large averaged set of lunars to firstly establish a surveying base point, and secondly to calibrate the chronometers used by the small surveying boats used for the detailed surveys thereabouts.

    One particular passage mentions that Worsley took from Elephant Island, for the famous James Caird open boat escape to South Georgia, the very last working chronometer from the stock of 24 working chronometers that had been put on board Endurance when she set out on her final voyage. It mentions also that Shackleton had taken a chronometer technician with him on Endurance to keep the initial stock of 24 chronometers in the best possible condition. These would have been 20th century chronometers, although they were enjoying 'a hard winter'. The design, maintenance, and particularly lubrication of mechanical chronometers for extreme conditions must have been ( perhaps still is ) something of a black art. Use a thin oil, and it falls out of the bearing parts in high temperatures on passage from the northern hemisphere towards Antarctica: use a thicker oil and the movement struggles in the cold once you get there.

    ISBN 978-0-00-751656-8

    Michael B

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