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    Re: George, is there a Part 4c?
    From: Arthur Pearson
    Date: 2004 Sep 25, 09:20 -0400

    Links to all four of George's "About Lunars" essays are listed together on
    the "Links etc." section of www.LD-DEADLINK-com. When part 5 is issued, I
    will faithfully post it in the same place.  Taken together, they are the
    original and still the best overall discussion of the lunar distance method.
    -----Original Message-----
    From: Navigation Mailing List [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]
    On Behalf Of George Huxtable
    Sent: Friday, September 24, 2004 7:16 PM
    Subject: Re: George, is there a Part 4c?
    Jim Thompson asked-
    >Was there a Part 4c to your very useful Part 4b
    Jim refers to a series of long-ago Nav-L postings, which, with posting
    dates, were
    About Lunars, part 1, 29 Jan.02
    About Lunars, part 2, 29 Jan 02
    About Lunars, part 3, 12 Feb 02
    About Lunars, part 4b, 24 Jan 04
    Perhaps these are still there in the archives if anyone wishes to go
    Jim asks about an issue 4c. The curious numbering of the parts came about
    because quite a lot of updating took place on part 4, mainly putting
    matters right when discussion on this list unearthed errors. So there
    existed first a part 4 and then a part 4a, but these should now be
    discarded, having been supplanted by 4b, the current version.
    What I think Jim is looking for is not 4c, but part 5, and maybe part 6.
    The present series ends (at 4b) with the navigator finding his Greenwich
    Time from a lunar. What remains to be written is a final part (or parts)
    showing how he can make observations for Local Apparent Time (at the ship)
    and then derive his longitude from the difference between these times.
    Finalising this series has become something of a family joke in the
    Huxtable household. I have promised to do so to myself and also to Nav-L
    members, and have started to write part 5, several times now!
    Let me explain the difficulties I have met. Nav-L members who follow lunar
    distances have a range of interests. Some want to measure lunars "as of
    today" from their boat or backyard, some with recently computed tables and
    a modern almanac, some in which a computer or pocket calculator does all
    the work. Some wish to follow old voyages or land-journeys, from old logs
    and journals, in which inland navigators would reflect their altitudes in
    an artificial horizon. Some are interested in using the same old log-trig
    functions and methods that were required of early navigators, others not.
    Over the years there has been a series of changes, particularly to the
    nautical almanac. It changed its time-scale from apparent to mean time, it
    introduced lunar distances for planets, later Greenwich Hour Angle took the
    place of Right Ascension. Methods for clearing the lunar distance developed
    throughout the lunar era (of say 1760 to 1860).
    Where I have found the greatest difficulty is in covering all these
    different aspects when explaining how to find a lunar longitude, without
    adding a great mass of inclusions and exceptions which would bog the reader
    down. I haven't given up, yet.
    So that series "About lunars" may be completed, with a part 5 and perhaps a
    part 6, but I have given over promising when.
    If any Nav-L members are keen on picking up the existing four parts of
    "About lunars" without delving into the archives, then on request I will
    repost those four (longish) messages.
    Yours, George.
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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