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    Re: New resource re ships' logs
    From: George Huxtable
    Date: 2010 Apr 6, 00:10 +0100

    Frank wrote, about the source of old ships logs and journals recently made
    available in the CORRAL website-
    "Hey, that's wornderful! Finally some primary source data from 19th century
    British vessels. "
    Much data has been available, via various libraries or the National Archive
    at Kew, but not online. I have recently investigated such data from early
    Cook logs and from Arctic whaling voyages, but none of these are in the
    CORRAL database. This is the first time, that I know of, that such a
    collection of digitised data has become available online. I hope there will
    be more..
    He asked- " Have you discovered any interesting navigational data in these
    logbooks yet?"
    No; as soon as I saw what was available, I thought to share the information
    with Navlist. Nor will I be able to do much investigation within it just
    now; it will have to wait a while. It's there for anyone that would like to
    burrow in.
    In the meantime, let me share something that has been puzzling me a bit,
    about observations from another Cook voyage.
    We noted, a while back, that the astronomical observations from Cook's
    third voyage (Bayly, Cook, and King) had been kindly made available on-line
    by the Canadians at-
    And if you go to page 43, that's a page showing lunar distance observations
    taken at Ulietea, in 1777. I took a look at this page in the hope that it
    would throw a bit of light on the observations taken at the same spot in
    the second voyage in 1773, because we had only a single page of transcript
    from that second voyage. It didn't throw much light, in the end.
    Note how the Sun column is shown as an altitude, but for some reason the
    Moon is shown as a ZD; presumably Zenith Distance. Why should this be?
    Well, it strikes me that this may be a use of the sextant fitted with
    backsight. If the Moon can only be seen over the island, so would call for
    an estimation of dip-short, can it be that instead, the Moon altitude is
    being measured up from the opposite horizon? Does that explain the use of
    ZD? Can anyone suggest another reason for logging ZD for one body, and
    altitude for another?
    Now to the bit that's been puzzling me. It relates entirely to the first
    four observations, on 7 Nov (nautical date). A set of lunars was taken by
    Cook and King simultaneously with different instruments, then another set,
    with the instruments swapped over, a few minutes later; a good, scientific,
    procedure. But the observations are very discordant, by over 4 arc-min,
    even though the index errors differ by only 35". And it's the two observers
    that are 4' apart, not the two sextants. And in the time interval, of over
    4 minutes, there's been no change in lunar distance. And the differences in
    deduced longitude don't reflect the differences in lunar distance. What's
    going on? It looks as if there were serious transcription errors. In which
    case, we have to be careful about accepting such tables of numbers at face
    value. Am I missing something?
    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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