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Dear D.H. Sadler



From wherever you may read this mail: Felicitation for your table
"CORRECTIONS TO BE APPLIED TO OBSERVED ALTITUDE, Refraction" which you,
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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