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    Re: refraction
    From: Guy Schwartz
    Date: 2007 Jan 4, 21:49 -0800

    Thank you. When I went to the link it costs $15.00 to download the if you
    are a member and $22.00 if you are not. I'll take your word for it and
    thanks to Lu too.
    I've said it before and I'll say it again, this group is such a valuable
    PS. if you have the article and would like to share it I would like to read
    ----- Original Message -----
    From: "Alexandre E Eremenko" 
    Sent: Thursday, January 04, 2007 7:52 PM
    Subject: [NavList 1979] Re: refraction
    > 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:
    > http://www.opticsinfobase.org/abstract.cfm?id=85182
    > 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:-)
    > Alex.
    > >
    > --
    > No virus found in this incoming message.
    > Checked by AVG Free Edition.
    > Version: 7.5.432 / Virus Database: 268.16.5/616 - Release Date: 1/4/2007
    > 1:34 PM
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