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    Slocum's lunars :was; long lost lunars
    From: George Huxtable
    Date: 2003 Dec 12, 12:56 +0000

    I doubt if Frank Reed and I are going to agree much about whether Slocum
    took just one lunar on his circumnavigation, or whether he made it a common
    practice. Perhaps it may have been something between the two.
    Frank argues that Slocum's position, South of Rio, that was agreed with a
    ship was by dead-reckoning over the few days since leaving Rio, and not by
    lunar. I agree that it's a plausible explanation, and doesn't prove (or
    disprove) that a lunar was taken at that time.
    Frank appears to accept the lunar longitude between Juan Fernandez and
    I quoted the account, a few days out in the Arafura Sea, in which Slocum
    says, after mentioning some noon Sun latitudes-
    "But the greatest science was in reckoning the longitude. My tin clock and
    only timepiece had by this time lost its minute-hand, but after I boiled
    her she told the hours, and that was near enough on a long stretch."
    Frank dismisses this-
    "He's talking about dead reckoning. If you want to know how far you've
    travelled in four hours, you need to know what four hours is. The minute
    doesn't matter much when you're doing five knots."
    I really don't see how Frank infers that Slocum's statement relates to dead
    1. Slocum used the word "reckoning" for both dead-reckoning and for lunar
    longitude, as in his account in the Pacific, off Nukuhiva, when he says
    "The verified longitude when abreast was somewhere between the two
    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?
    3. I'm sure Frank and I would agree that that tin clock wasn't being used
    for any form of "longitude by chronometer".
    4. If it was just a matter of dead-reckoning from a log, why would Slocum
    refer to it as "the greatest science"?
    We have to remember that Slocum was writing a journal for the ordinary
    reader, not a log for the interest of Nav-l listmembers. Having described
    taking lunars once, in the Pacific, we shouldn't expect him to refer to
    each lunar observation thereafter in his text. He must have taken hundreds
    of noon latitudes in the voyage, but only occasionally did he refer to
    doing so in his account. It is indeed a pity that his log no longer exists.
    Slocum devoted more space to the places he arrived at, than to the passages
    So we can't infer, from a shortage of references to lunars, that (except
    for that once) he didn't take them. Nor, I accept, can we infer that he was
    taking them all the time. The truth may lie somewhere in-between. But it's
    a clear claim by Frank that I argue with, a claim that Slocum used lunar
    distances only once, in the Pacific. Sparsity of evidence for is not the
    same as evidence against.
    We know, from his son Victor's account, that he made a practice of checking
    his chronometers against lunars, during his long career as master of a
    merchant vessel, perhaps one of the last ship's captains to do so. So he
    was very familiar with the required skills, though may have got a bit
    Sorry to have misplaced a comment made by Slocum, from his Pacific passage
    where he made it, to the Indian Ocean (as Frank pointed out).
    Frank added->And you wrote:
    >"In the hands of skilful observers and patient computers the Lunar Method is
    >reliable within a quarter of a degree longitude, which would be the distance
    >of a high landfall..."
    That was me quoting the words of Slocum's Son Victor, not my own words. I
    wouldn't really disagree, though for observations at sea I suspect it was a
    bit optimistic.
    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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