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    Re: Measuring Dip in the 18th Century
    From: Alexandre Eremenko
    Date: 2014 Jan 1, 17:00 -0500

    Brad and Gary,
    
    > 4) that he used Copernicus' mighty work as a reference, a mere 54 years
    > after its publication (!!)
    
    I just checked Copernicus: he says "we with some other our contemporaries
    found that the inclination of the ecliptic is 23d 29' "
    (Then he discusses Ptolemy's number 23d 51' 20", and concludes that
    this angle decreased since the time of Ptolemy, contrary to Ptolemy's
    assumption that it is constant).
    The 1' difference between Copernicus and Wrignt confirms that Wright
    did his own observation instead of copying this number from Copernicus.
    
    The accuracy of his number is the evidence that he took care about the dip
    and other things that could contribute more than 1').
    
    Copernicus (like Ptolemy) does not really describe his instrument
    or the details of his observations. Instead he writes in general
    how the instrument can be made etc. These descriptions raise doubts
    that they (Ptolemy and Copernicus) really performed the observations
    themselves:-)
    
    Alex.
    
    
    > There are some points which must be deduced from the text
    >
    > A) the quadrant uses the horizon for the reference.  Other than specifying
    > London, Wright does not tell us what body of water is used.
    > B) Wright does not tell us a dip table was used.  We can assume that it
    > was, because unless the HoE was 0, then the observation would have been in
    > error by that amount.
    > C) Wright does not inform us as to whether the observation was ship or
    > land
    > based.  There are problems with either one.  If land based, then the TIDES
    > affect the measurement, unless one can guarantee the same tide height for
    > minima/maxima observations 6 months apart.  If water based, the pendulum
    > referenced as establishing vertical would be challenging at sea.
    >
    > One additional point can be made.  The assertion that a quadrant is only
    > good to 10 arc minutes can be readily disposed of.
    >
    > Brad
    >  On Jan 1, 2014 11:42 AM, "Alexandre Eremenko" 
    > wrote:
    >
    >> ------------------------------
    >>
    >>
    >> Gary,
    >>
    >> > I have also attached the June page showing Wright's
    >> > determination of the Sun's maximum declination as 23� 30'
    >> > north while the
    >> > modern value is 23� 26.3' a difference of only 3.7'.
    >>
    >> Did you take into account that obliquity of the ecliptic
    >> decreases at the rate about 0'.7 per century?
    >> More precisely, 46".8 per century.
    >> This implies that Wright wrote it correctly.
    >>
    >> I have not read the book yet:-)
    >> but I assume that he was using some astronomical tables available at
    >> that
    >> time, or did he determine all astronomical constants himself??
    >>
    >> Alex.
    >>
    >>
    >>  I have also included
    >> > Wright's explanation of how he determined the Sun's declination.
    >> >
    >> > http://en.wikipedia.org/wiki/Gregorian_calendar
    >> >
    >> > gl
    >> >
    >> > gl
    >> >
    >> > Attached File: http://fer3.com/arc/img/126089.march declination table
    >> from
    >> > wrights book.jpg
    >> >
    >> > Attached File: http://fer3.com/arc/img/126089.june declination from
    >> > wrights book.jpg
    >> >
    >> > Attached File: http://fer3.com/arc/img/126089.explanation of
    >> declination
    >> > determine by wright_page_1.jpg
    >> >
    >> > Attached File: http://fer3.com/arc/img/126089.explanation of
    >> declination
    >> > determine by wright_page_2.jpg
    >> >
    >> >
    >> > View and reply to this message: http://fer3.com/arc/m2.aspx?i=126089
    >> >
    >> >
    >> >
    >> >
    >>
    >>
    >> View and reply to this message: http://fer3.com/arc/m2.aspx?i=126097
    >>
    >
    >
    > View and reply to this message: http://fer3.com/arc/m2.aspx?i=126100
    >
    >
    >
    >
    
    

       
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