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    Re: Problem with a sextant
    From: Alexandre Eremenko
    Date: 2006 Apr 25, 12:19 -0400

    Yes, he gives a complete list of his equipment:
    A Hadley's Sextant, made by Dollond,
    Another made by Ramsden.
    They are described on page xxii
    (just downloaded from that site we are discussing
    last weeks).
    The Ramsden one is 15 inch radius made
    of "one solid plate of hammered brass"
    1/9 inch thick (I can only imagine how heavy it was:-)
    Wales calls it "the best instrument I ever handled".
    The Dollond one is also of metal and was a bit lighter.
    So probably he had better instruments than I have:-)
    So I am very curious in his real observation errors.
    As I cannot pinpoint the places where he observed,
    I can only judge about his random, non-systematic
    errors, which can be seen from his sigmas and spans.
    Fortunately he gives very long series of observations
    from land and from anchor stops, together with
    observations of another observer, William Bayly, who
    used two (metal) Ramsden sextants.
    On Tue, 25 Apr 2006, Ken Muldrew wrote:
    > Does he say what kinds of sextants (quadrants) he is using? If one was
    > made of wood and the other metal, then changes in humidity would change
    > the dimensions of the wooden instrument. Alternatively, two sextants made
    > from different metals would expand and contract differently with
    > temperature. These would be small changes, but they might be enough to
    > show up when making arc measurements to a part in 10,000 or better.
    > Ken Muldrew.

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