Next message: Peter Fogg: "Re: CLEANING SEXTANTS"
George H wrote:
"So, it seems to me, in the 70 years or so between Mendoza's publication and
Merrifield's, lunar-distance navigation had taken a serious step backwards.
Such is progress!"
Well, perhaps it's not completely surprising. We're seeing degeneration in
action. By 1884 lunars were essentially finished. It might seem strange that
something like Merrifield's method could even find an audience. Why wouldn't it
have been immediately ridiculed for the reasons you cite? I think the simple
answer is that no one was paying much attention any longer. Lecky was not alone
in thinking lunars as dead as Julius Caesar. The handful of old conservatives
who occasionally shot lunars at that late date presumably used methods that
they knew and loved and would not necessarily have noticed this Merrifield
method. Young students forced to do lunars to pass an exam would have studied for
said exam, learned the method recommended by the textbook, and promptly erased
the memory when the exam was over. Junk can get into print when no one is
reading the articles...
Also, I mentioned a logbook from 1809/10. The navigator on that voyage shot
lunars on a regular basis (usually for two or three days every two weeks right
around first quarter and last quarter) and cleared them by Witchell's method
but he *never* calculated the Q correction (the Norie table XXXV correction).
When I have time I would like to see if it would have done him any good to add
it, but I doubt it. First, the correction is negligibly small if you limit
yourself to elongations near 90 degrees, and it seems to have been rather common
to do just that in this period. But maybe more importantly, in this era when
dead reckoning was paramount and global charts were poor, I have the impression
that the longitude was always assumed to be relevant only to the nearest
degree. It wasn't in their mindset to believe that lunars could provide them with
a true longitude as accurate as a latitude. That shift in attitude did not
arrive until chronometers became common.
George, are you able to access this web site and view the pages:
http://visualiseur.bnf.fr/Visualiseur?Destination=Gallica&O=NUMM-55891 ?
If so, next question: do you read French? If you can answer yes to both
questions, then go to page 96 and enjoy. It's Mendoza y Rios writing about the
general methods of series solutions to the problem of clearing lunars. The whole
paper beginning at page 43 is interesting, but the material that's immediately
relevant starts fifty pages later.
I'm guessing right now that the French is no problem, but the web site may
present difficulties. If so, I have a couple of ideas.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
