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    Re: Slocum's lunars
    From: Jan Kalivoda
    Date: 2003 Dec 13, 12:46 +0100

    I has three objections to Frank's conclusions:
    The explanation of the expression "the greatest science" as a guess of the
    longitude from crossing the border of two distinct currents off the coast
    (or a guess of the effects of the stream and the wind effects for DR in
    general) seems to be exaggerated by Frank. It is undoubtely the great
    navigational skill and "art", but a sort of science? Maybe, Slocum had
    understood this word in this sense, but I doubt.
    The existence of  constant latitude legs in Slocum's narration isn't a proof
    that lunars weren't taken. Yes, Moore and Bowditch use lunars for running
    from A to B direct way in their examples "The voyage from Portsmouth/Boston
    to Madeira", but this wasn't the general method for using them. Lunars were
    unreliable to the extent of a half degree of longitude at sea at least,
    therefore they were rather used on "constant latitude legs" to verify the
    longitude obtained by DR, if used at all. (Frank's interesting reference to
    logbooks proves it.) There was a discussion about that matter in
    the list this year. I haven't the link now, but use ship's name "Arniston"
    for finding it, if you like. That ship was lost near the Cape of Good Hope
    in early 1800's, because the master hadn't a chronometer and neglected
    lunars on the constant latitude leg.
    Slocum's mention about the error in logarithmic tables cannot be explained
    as a hint at his own error, which he sought to hide by pretext of erroneous
    tables. Such tricks are common for beginners that failed the resolve the
    task, but Slocum wasn't a beginner and he resolved his task of these unique
    clearly attested lunars very precisely after all near Nukuhiva (if he isn't
    a liar in your eyes). Some months ago, I supposed for explaining this place
    of Slocum's story that Slocum used some "approximate" method for reducing
    lunars, as there were errors in various tables of this type. Their value
    could be called "logarithm" by Slocum, too, as old navigators used this term
    not only for true decadic logarithms of pure trigonometric functions, the
    only necessary logarithms in "strict" methods, but also for logarithms of
    many auxiliary and sometimes complex values given in special tables. One
    look into old explanations for users of these tables can prove it.
    Jan Kalivoda

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