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From: Henry C. Halboth (no email)
Date: Sat Sep 11 2004 - 13:50:36 EDT
It is high time that a few of the comments/questions raised
concerning my posting regarding Arnold's Method of clearing
Lunar Distances be addressed. Sorry for the delay.
Preliminarily, thanks to all those who did respond. Your comments
were certainly insightful and conducive to the advancement of our
discussions. Many of the older methods of navigation are fading
into obscurity or are sometimes simply misrepresented - this forum
provides an informative arena for there correct preservation. If you
get it wrong, you are going to be stomped on, which often is not
the case with published material.
As regards Arnold's tables being somewhat restrictive by reason
of constraints in altitude correction, please note the use criterion
to be the bodies apparent altitude or the correction thereto; how either
is calculated is not mandated and may be at the user's option -
whatever refinement in the way of temperature and latitude
corrections for refraction and parallax may certainly be applied
at discretion. One cavalier treatment, not previously mentioned, is that
Arnold advocates a standardized observed altitude correction to obtain
the apparent altitude; under a Rule III, he advocates, across the board
...
"To the moon's observed altitude, add 12', if the lower limb be taken,
but if the upper limb be taken, subtract 20'. to the observed altitude of
the sun's lower limb add 12', and from the star's observed altitude
subtract 4', and you will have their apparent altitudes." Of course,
we know this to be technically incorrect - perhaps it is simply a
reflection of the often expressed opinion that an error of a few
minutes of arch in altitude does not materially affect the result in
clearing the distance.
As to the longevity of Arnold's work, addressed by Frank, it is
probably worth noting that his work is not primarily a navigational
text. It is a wide ranging compendium of nautical knowledge, trivia
if you will, specific to the era it which it was written; it possesses
no ongoing values that might attract it perpetuation by a hydrographic
office or on which subsequent authors/publishers might build on a
continuing basis, as occurred both with Bowditch and Norie, although
it seems Norie has pretty much run it's course, as the last edition I
was able to obtain was that published in 1917. Subjects covered by
Arnold in some 844 pages, exclusive of tables, include sailing
directions, ship maneuvering instructions, sailing instructions,
practical sea gunnery, familiar subjects in astronomy, the pepper
trade on the West Coast of Sumatra, UIS Customs Duties, coins
of the US, instructions to Masters of Ships, quarantine laws, laws
of pilot and pilotage, regulation of seamen in the Merchant Service,
marine assurance, etc. It is really a snapshot in time and contains
priceless information, some of which has long since been forgotten,
of a particular era in seagoing history and the United States. It bears
a frontispiece of testimonials, albeit unsigned, by prominent marine
figures of the day.
There are about 103 pages devoted primarily to Lunar Distances
and the associated astronomy and, as far as my personal interests
were served, allowed a greater understanding of the lunar theory
than did either Bowditch or Norie which, in my view, were more
prone to simply providing rules of calculation rather than in appealing
to the reader's understanding of the problem.
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