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    Re: refraction
    From: Alexandre Eremenko
    Date: 2007 Jan 4, 22:52 -0500

    On Thu, 4 Jan 2007, Guy Schwartz wrote:
    > How were the refraction adjustments
    > initially calculated for the atmosphere?
    > What was the methodology used?
    > I don't think it was as easy as the stick in the
    > water method?
    The principle is easy.
    Positions of stars (and motion of Sun)
    were known since long ago.
    With higher and higher precision gradually.
    Taking their apparent altitudes and comparing with
    computed altitudes you can find refraction.
    I don't know precise historical details, but I am sure
    that Ptolemy was well aware of refraction.
    The theory explaining refraction is of much later origin
    probably of XVII century. Once you derive a formula
    on a theoretical basis, you need only few precise
    observations to determine numerical coefficients in this
    formula and to test the theory. The modern tables
    are computed using this formula.
    (I compared the formula with the Almanac, it matches:-)
    I wanted to finish this message with the words
    "But I do not know the precise history of events"
    but then I typed on Google:
    atmospheric refraction history
    and the first site which popped up was:
    with the paper
    Atmospheric refraction: a history
    by Waldemar H. Lehn and Siebren van der Werf.
    The full text is downloadable in PDF (for me)
    but I am not sure that it is downloadable for everyone.
    If not, tell me and I will e-mail you the paper.
    Rare luck! Usually Google returns 175,000,000
    sites with total irrelevant junk when I search:-)
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