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    Re: Refraction
    From: Marcel Tschudin
    Date: 2005 Aug 19, 19:24 +0300

    Dear D.H. Sadler
    From wherever you may read this mail: Felicitation for your table
    together with your colleagues, compiled and published 1952 in the Journal of
    the Royal Institute of Navigation; this table became really a contribution
    of enduring value. I just wanted to let you know that what you published
    more than half a century ago is still being published in regular intervals
    by the National Imagerie and Mapping Agency in their Sight Reduction Tables
    for Air Navigation, Pub. No. 249 and, from what I was told, also in the Air
    Almanac. Your table was by the way the only publication I was able to find,
    when I was searching these days of the year 2005 for published refraction
    values for negative altitudes.
    May be you know that we have come here in to the age of computers. But
    believe it or not, this could not change anything to what you derived by
    hard manual work. From what I notice, not a single figure has been changed
    in the meantime. Could it be, that these days, where everybody has a
    computer, one concluded, that it would not being worth updating your table
    since everybody would now be able to calculate these values and, as a
    result, your table was just left there for historical reasons? Or, was your
    table left in these handbooks for all those enthusiastic hobby-sailors, who
    still like to navigate with sextant and tables? Yes, you might not know that
    navigation became now less a profession and more a hobby. Technique has so
    much advanced, that with the help of some satellites circulating around our
    planet and with some fancy electronic equipment anyone can be now a
    professional navigator, finding even out whether he/she is in the bedroom or
    in the living room (just in the case he/she would not know it).
    Your table is in my view more than just a historical relict. I find it a
    useful collection of benchmark values. Benchmarks are very helpful to all
    those who try to calculate something in order to have a reference for their
    results. Since with the help of computers it is now possible to do more
    refined calculations, I would like to ask you for your kind permission, for
    having your table updated by using the newest calculation procedures and
    also using the newest atmospheric models. As you know, there want be drastic
    changes, only some refinements of the results which you and your colleagues
    already obtained. Those new derived data would then however correspond to
    the calculation capabilities and the knowledge of this time at the beginning
    of the third millennium.
    Thank you for your attention. Awaiting your reply, I remain
    Yours sincerely
    Marcel E. Tschudin

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