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    Certificates and arc excentricity
    From: Alexandre Eremenko
    Date: 2007 Oct 24, 16:48 -0700

    In my recent message on the paper of White, I mentioned as
    "ridiculous" his reason for
    not applying the arc correction to his observations. This was so
    strange to me that I made
    a little investigation.
    
    Actually the determination of the arc correction was apparently a big
    problem in 1850-s.
    And the ordinary seamen did not know the arc correction of their
    sextants.
    Simms (of the famous Troghton and Simms) wrote several papers and a
    book
    where this is the main subject. This was in the late 1850-s.
    
    The arrangement tor measuring the arc correction was installed in the
    Kew observatory
    approximately in 1867 (not later). And perhaps from that date one
    could provide
    a sextant with a certificate. I don't know exactly when they started
    to issue certificates.
    
    White had a sextant (by Troughton) made "in the beginning of XIX
    century", so it
    did not have a certificate. He (White or someone else) actually
    determined the arc correction,
    and he knew it when he made his observations in 1889, but he thought
    that at that time
    an ordinary seaman would not know his arc correction.
    And he intentionally neglected it in his published observation.
    
    In England, you could probably bring your sextant to the Kew
    observatory and obtain a certificate
    for certain fee. Probably it was harder to do in Australia in 1889.
    
    Alex.
    
    P.S. Of course this does not remove the question how did it happen
    that he obtained the results
    within 10" of the truth if he neglected the arc correction of his
    sextant which was up to 20".
    
    
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