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    Re: Instumental error?
    From: Alexandre Eremenko
    Date: 2005 Apr 20, 14:45 -0500

    Fred,
    I apologize to you and to the list:
    I mistyped the web address.
    The corrected address is:
    http://adsabs.harvard.edu/cgi-bin/
    nph-bib_query?bibcode=1888AN....118Q.383S&db_key=AST
    (Again, remove carriage return!)
    In general, this archiv contains about 30 XIX century
    papers with keywords "sextant", "errors", "eccentricity" etc.
    I am glad it is free.
    
    The author speaks of a meridian circle rather than a theodolite.
    Somehow on the first reading I had a wrong impression
    that the trick can be done with an ordinary theodolite.
    But when I started to explain this to the list, I encountered
    difficulties, so I looked at the paper again, and noticed that a hudge
    objective lens is required.
    
    The ordinary methods involving theodolite are probably
    the "outdoor methods". I mean you put some vertical sticks
    on a large distance from your position, and measure the horizontal
    angles with your sextant and then with theodolite.
    The large distance is required because you cannot assure
    that both measurements are exactly from the same position.
    For example, if you need 0.1' precision, and are
    able to keep the position to 1 inch (I doubt is is easy to
    do better than that,
    even with sophisticated tripods), the sticks should
    be at the distance of 3400 feet which is hard, of course.
    
    Any indoor method I can imagine would use one or several reflecting
    surfaces, but the problem of crating parallel rays is hard.
    
    
    Alex.
    
    
    

       
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