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    Re: horizon mirrors: was [NAV-L] Question about Davis Mk 25 sextant beam converger
    From: George Huxtable
    Date: 2006 May 10, 22:20 +0100

    It seems that message distribution from Nav-l is
    still failing.
    The following message (copied again below) was
    sent several
    hours ago. Normally, I would expect to get a copy
    reflected back from Nav-l rather promptly. But
    none has arrived here.
    It was certainly received and posted up, because
    GregR has since responded to it.
    If I have failed to receive it, perhaps others
    have as well. That's why I am resending the
    message, and will keep on resending until I
    receive a copy.
    Of course, it doesn't matter, to me, whether I
    receive that message or not, because I know what's
    in it. But knowing that that one was lost, how
    many others have failed to get here, that I am
    unaware of? It's a serious problem, that calls for
    | On May 03, GregR asked-
    | "I bought a Mk 25 sextant a couple of weeks ago,
    | and am wondering about the accuracy of the beam
    | converger (it's a full-horizon model vs.
    | split-mirror) "
    | I think between us Nav-L members have resolved
    | GregG's problems for him, but it may be worth
    | discussing again the values of what Davis call a
    | "beam-converger", and others call a full-horizon
    | or full-view mirror, as opposed to the
    | half-horizon mirror, silvered across only half
    | width.
    | What's brought it to mind is a thoughtful note,
    | (together with an abstract of the Davis patent
    | about their version) in the Spring issue (No 91)
    | of "The Navigator's Newsletter", by its new
    | Editor, David Burch (of Starpath). That
    | journal, issued to members of the Foundation for
    | the Promotion of the Art of Navigation, has been
    | through a very lean patch, but has recently been
    | thoroughly transformed, I'm pleased to say.
    | A few Nav-l members pop up in that journal. For
    | example, Bill Murdoch (a name familiar to Nav-l
    | readers) has contributed about that Davis
    | I won't copy details of that note, except
    | "nutshell summary", which goes as follows-
    | "Full-view mirrors make the easy sights easier,
    | and the hard sights harder."
    | That view corresponds exactly with the reports
    | the "traditional" navigators, using lunar
    | distances, in the 2001 re-enactment for the BBC
    | a leg of Cook's first circumnavigation. They
    | that in daytime a high, pale, Moon was invisible
    | against a milky sky using a full-view mirror,
    | showed up clearly with a split mirror. It was a
    | question of contrast.
    | For anyone interested, the foundation is run by
    | Terry Carraway, and the subscription for members
    | in the US is (I think) $30. The website address
    | is-
    | www.navigationfoundation.org
    | the address is PO box 1126, Rockville, Maryland
    | 20850, USA.
    | Phone or fax is 301-622-6448
    | navigate1@comcast.net for emails.
    | George Huxtable.
    | contact George Huxtable at
    | george@huxtable.u-net.com
    | or at +44 1865 820222 (from UK, 01865 820222)
    | or at 1 Sandy Lane, Southmoor, Abingdon, Oxon
    | 5HX, UK.

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