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    Re: Slocum's lunars
    From: George Huxtable
    Date: 2003 Dec 13, 01:49 +0000

    I am quite convinced, by the arguments of Frank Reed and others, that
    Slocom's observations South of Rio, that he shared with a steamship, had
    nothing to do with lunar observations.
    I am not convinced by his arguments that near Timor he was finding
    longitude entirely by dead reckoning.
    I said-
    >"2. He towed a rotating log, which would indeed give him information about
    >longitude; particularly on a mainly West-going passage, as this was. But
    >for that, there was no input AT ALL required from a clock. It wasn't a
    >speed-log, it was a distance-log. So why would Slocum refer to his clock,
    >if that log was where his longitude was derived from?"
    and Frank answered-
    >You still need some basic clock when you do DR navigation. At minimum, you'll
    >want to record your position at a regular time every day, let's say, 4pm, or
    >once every four hours when closer to shore. A beat-up old clock would serve
    >fine for this purpose as would a good sandglass.
    Well, presumably Slocum was taking a daily noon latitude whenever he could.
    We have recently been discussing that you can't get precise time from a
    noon observation. But it would certainly give Slocum a guess at noon that
    would be good enough to decide when to record the reading of his distance
    log. So I am not impressed with that argument,
    However, there's another factor that weighs against my contention and in
    favour of Frank's.
    Spray set off into the Arafura Sea on 24th June 1897, and Slocum noted-
    "It was my good fortune to enter the sea on the last quarter of the Moon,
    the advantage being that in the dark nights I witnessed the phosphorescent
    light effect at night in its greatest splendour." I have checked by my
    pocket calculator that New Moon wll have been on 29th June (a crosscheck
    would be useful, please) and Timor was in view from Spray on 2nd July.
    Slocum's text that I quoted from appeared to relate to the days prior to
    Timor. That crossing of the Arafura Sea would have been the worst possible
    time for observing lunars. Lunars would have been possible in the 2 or 3
    days of the passage, but that's not very helpful for predicting a landfall.
    It might have been possible to use a lunar on the last night before
    sighting Timor, but no earlier, I think.
    So I have to accept that the evidence for lunar observations in that part
    of the voyage is now somewhat flimsy.
    Finally, I said-
    >"It is indeed a pity that his log no longer exists."
    and Frank asked
    >Just to clarify, you're sure of that? This was one of the things I've been
    >trying to find out.
    It's no more than a presumption. If it still existed, that document would
    be famous now, and it would have been copied to death. As that hasn't
    happened, I presume it's been lost.
    I would like to be proved wrong on that one, too.
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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