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    Re: How Many Chronometers?
    From: George Huxtable
    Date: 2009 Sep 17, 11:11 +0100

    In [9766], Gary recorded a disagreement with my suggestion that one can do
    little to protect a sensitive object, such as a crystal oscillator, from
    environmental changes in ambient temperature, by such means as wrapping it
    in blankets. I claimed that this could have only a short-term effect, and
    that the ambient changes would always get through in the end.
    He wrote-
    "So I disagree with George to the extent that if the watches are kept in
    an insulated box, to limit the effect of diurnal changes in cabin
    temperatures, then the change in rate will only happen based on long
    term changes in ambient temperature, say on a cruise from the Caribbean
    to England. But, if the cabin is kept in a range of temperatures which
    are habitable for humans then the change of rates can be kept to a small
    I recall that as a child, British winters, in a house with only local
    heating, were made tolerable at night only by using a hot-water-bottle (such
    aids may be unknown and unnecessary in the USA). And I recall how rapidly
    such a bottle would lose its heat, though wrapped in blankets with me, so
    that before very long it was a pleasure to kick it out. I also recall the
    use of a vacuum "Thermos" flask to keep cups of tea hot, and their failure
    to do so for more than a very few hours. This in spite of the fact that some
    pints of water were involved, a substance which has the highest
    specific-heat of any, which means that it holds more heat, and keeps its
    temperature, longer than anything else. Gary's crystal oscillator in a
    blanket, without such heat-ballast, would not keep the outside temperature
    at bay for long, but with a bottle of water to keep it company, he might
    increase its thermal time-constant to a few hours; not for days, however.
    As for his "range of temperatures which are habitable for humans", there
    might well be different views on that from different societies in different
    eras. A week ago, I was looking over HMS Cavalier, a World war 2 destroyer
    built in 1944; the sort of ship that escorted Arctic convoys to Murmansk and
    Archangel in Northern Russia, Summer and Winter. She was refitted in 1957
    and retired in 1974. Yet still, she had a completely open bridge, without
    windows, and only a dodger to keep the weather off. And I was rather
    surprised to find, tucked away on that open bridge, sheltered from rain but
    from nothing else, electronic gear such as a radar display.
    How, I wonder, would modern American bridge-teams, sheltered from the world
    in their air-conditioned cocoons, without even an open bridge-wing to walk
    out on to, have fared under such conditions? Or in the environment accepted
    by some present-day small-craft sailors, the ones that venture away from
    tropical trade-wind sailing?
    The "bridge" got its name from an open lattice structure, that bridged the
    gap between the top of the paddle-covers, to provide an all-round view. From
    such a perch, steamers in their thousands were conducted across the North
    Atlantic, the year round.. In thick weather, a lookout was expected to be
    stationed at the fo'c'sle head; no shelter provided. These were considered
    to be habitable conditions then, but I doubt whether Gary would describe
    them so now.
    Polar explorers, by the way, would carry sledge chronometers: pocket
    watches, slung round their necks inside their furs, essential for guiding
    them back to base along the correct longitude. When Shackleton's Endurance
    went down in the Antartic ice in 1915, the ship's box-chronometers were
    abandoned with the ship, and from then on the expedition relied on four such
    pocket-chronometers. Only one of those remained in working order throughout
    that remarkable journey from Elephant Island to South Georgia, being
    essential for Worsley's feat of small-craft navigation.
    Together with Brad, I'm intrigued by the type of yoga that Gary adopts to
    enable him to read a chronometer that's duct-taped to his belly.
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    NavList message boards: www.fer3.com/arc
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