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    Cook's observations, was: Problem with a sextant
    From: Alexandre Eremenko
    Date: 2006 Apr 25, 21:45 -0400

    Dear George,
    > It seems like he had a serious problem.
    > A degree and a half of longitude corresponds to about 3 arc-minutes of
    > divergence between
    > the two instruments. That's a lot.
    I am reading his journal trying to find out more about their observations.
    In some cases they record which sextant was used in other cases they
    I have no means to compare their observations with their actual
    positions (though for their observations from shore, this could
    be possible in principle, they stayed in the cities sometimes,
    even mention British Consulates:-)
    But I can judge about their random errors by analysing sigmas
    derived from long series taken on the same place. These sigmas differ
    substantially. So far I worked out only few series but already have some
    preliminary observations.
    1. Sigmas in series of 5-10 Lunar distances vary from approx 0'.5
    to 0'.8
    3. All 4 sextants have very similar performance (Dollond and Ramsden
    of Wales, and two Ramsdens of Bayly).
    4. The strange thing is that "one foot astronomical quadrant"
    by Bird, a stationary instrument, as I understand, hase the
    same performance as the hand-held sextants.
    5. The index correction of their sextants vary from day to day
    sometimes by 0'.5 and more.
    With these preliminary observations I may conclude that
    my SNO-T is not worse than the best instruments of 1770-s.
    In my series of Lunars sigmas are usually smaller,
    and SNO-T holds its IC constant for long periods of time.
    > A possible explanation might be collimation error.
    I doubt it. Wales was an experienced observer,
    collimation error is easily checked and easily corrected.
    And he says he did everything he could...
    > It would be a service if someone would survey the almanacs of the
    > lunar-distance era, and tabulate the day-by-day errors in those predictions.
    I agree. This seems to be easy (using Frank's calculator, for example)
    but very time consuming.
    > student to correlate modern predictions with the contemporary ones,
    > even stirring from his keyboard. Anyone interested in such a project?
    Unfortunately, I don't know where to obtain this student:-(
    Mathematics students would not be interested
    (this will not help them to advance their careers)
    and such science as "history of mathematics"
    (not speaking of history of astronomy or navigation)
    is not cultivated in this country, at least in the universities
    that I know:-(

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