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    Re: Refraction
    From: Robert Eno
    Date: 2005 Sep 3, 11:42 -0400

    No worries Marcel,
    I used the term "black magic" rather flippantly, however, my understanding
    is, nothwithstanding that there is a lot of "physics" behind the refraction
    formulae, that the behaviour of the layers of air which causes refraction in
    the first place, is so variable that the mathematical formulas can only give
    an approximation, albeit reasonable accurate, of what the refraction error
    will be.
    This reminds me of a few questions which I posed some time ago, but to which
    no one responded:
    What atmospheric and weather conditions would you consider to be ideal for
    taking sextant observations at sea? Why?
    What atmospheric and weather conditions would you consider to yield
    observations of questionable value? Why?
    I am excluding sea state here, but for argument's sake, let us assume that
    the seas are flat calm.
    Perhaps with this discussion about refraction, I will get some responses.
    ----- Original Message -----
    From: "Marcel E. Tschudin" 
    Sent: Thursday, August 04, 2005 10:38 AM
    Subject: Re: Refraction
    > Thank you Fred and Robert for all your support.
    > I found finally the "Table 6 - Refraction", previously Table 8... This
    > sould
    > help to derive some sort of table or function.
    > I do not quite agree with "black magic", it is actually very basic physics
    > which can be calculated by integration over air layers. May be some one
    > out
    > there has even a programmed source code to do this. I actually came across
    > a
    > Basic program, but it can not handle negative altitudes, where certain air
    > layers have to be passed twice. Furtheron, I am unfortunately not in a
    > position to adapt that Basic code to my needs.
    > So, as for the moment, I try to go on with this Table 6.
    > Marcel

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