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    Re: How Many Chronometers?
    From: George Huxtable
    Date: 2009 May 9, 10:05 +0100

    What a remarkable resource is Navlist! Within a few hours of expressing
    puzzlement about aspects of a paper on chronometers and lunar distance, in
    come two plausible explanations, from Henry Halboth and from Paul Hirose. If
    forced to choose between them, perhaps Paul's explanation, that observations
    were made from the near limb of the Moon to both East and West limbs of the
    Sun, fits the notation better, though I had not realised that it was a
    general practice. Thanks to both.
    But I remain puzzled about Toynbee's discussion of the implications of the
    differences between those observations. If Paul's explanation is correct,
    they relate to nothing more than different assessments of the apparent
    diameter of the Sun, but Toynbee seems to think there's more substance in it
    than that.
    Still, those numbers at the foot of the page about "maker's error" seem to
    elude all, and I wonder if there's a typo in it somewhere. We'll never know.
    Henry added-
    "We are also not advised as to whether or not the Captain had access to the
    newly calculated Lunar Tables which came out about the time of the published
    observations - I know only that the American Almanac first contained the new
    tables in 1855, but that does not necessarily mean that they might not have
    been available elsewhere before that date."
    I think that here Henry refers to Hansen's Lunar Tables, which were printed
    (financed by the British Government) in 1857, but weren't incorporated into
    the British almanacs until 1862. I understand that the American almanac was
    far more progressive than the British one around that time, and can quite
    believe that they had got on to the new tables first, by 1855. But either
    way, the improvements to Moon predictions that Hansen made, which were
    signifcant, would not have been available to Toynbee in 1853. By that date
    rather serious systematic errors had developed in the lunar predictions,
    which hadn't improved much since Maskelyne's days. They could have played a
    part in the errors seen by Toynbee.
    Henry also showed suspicions about the exclusion of some data, and I agree
    with him about that. It's always tempting for an observer to exclude data
    that doesn't fit his preconceptions, but it's a dangerous thing to do.
    Toynbee says, about these rejects, "...they were deemed but indifferent
    observations before working them", but I, too, am suspicious about such
    Henry might not be aware that to me, and perhaps to others, his message came
    across encoded rather oddly, though it was quite possible (though a bit
    disconcerting) to read its text. Each paragraph was preceded by a line such
    as this-
    and the complete message was in Unicode, and spilled over the ends of the
    displayed lines on my screen, requiring use of sideways-scroll to read each
    full line, until I reduced the character size. I don't know whether it
    relates to a problem at my end, or his, but inward emails from others don't
    behave that way, and neither did previous postings from him.
    Henry made some general points about precision of observations which are
    likely to lead to further discussion, as it's a popular topic with various
    strongly-held viewpoints. I have therefore separated it out and started a
    new thread.
    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.
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
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