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    Re: Sumner's Line (Navigation question)
    From: Bill B
    Date: 2006 Feb 14, 19:33 -0500

    > I wonder, though, why Bill is still so unwilling to splash out $14 on
    > the paperback, which  will tell him all he wants to know.
    If it were available at my local bookstore, it would be in my hands by now.
    I do like to gang my purchases from Celestaire to reduce shipping costs, and
    am not ready to make my spring order yet. (Sailors can be notoriously
    frugal.  A power boater sees something and asks what colors it comes in, and
    buys three.  A sailor thinks, "I wonder how I can make one of those?") You
    can rest assured it is on my list.
    Frankly, there is so much more that I noticed in my quick read that I want
    to explore. His celestial LOP discovery was a breakthrough, and gives
    exactly the same LOP that current methods do.  Past that, it seems he was
    thinking 100 years ahead of his time in some cases. I am surprised
    mathematicians did see problems to be solved and jump on them almost a
    century earlier.
    > Bowditch, in condensing Sumner's account to a single page, omits a lot more
    > than that.  For
    > example, Sumner provides a full page of numerical calculation on page 15.
    Indeed,  which I found somewhat curious (pgs 16 & 17 in the online version).
    In Sumner's recounting he was moving his latitude in 10' steps, but in
    example I all other elements seem to sync up, but if I am reading it
    correctly he is working in 1 degree increments (51 N and 52N) to establish
    an LOP.  I did time sights using those latitudes, and the longitudes agree
    with the 51d and 52d N example.
    > | 3. The Bowditch account omits the DR latitude.  This is the major sin of
    > | omission, as if covers up (IMHO) that fact that latitude scale in the
    > | Bowditch figure is off by approx. 5 degrees.
    > Does Bill mean 5 minutes?
    Yes, my mistake.  Good catch.
    > ...and loaded Sumner's Plate III to the list's
    > dedicated blackboard site...
    Thank you for your kindness.
    > My Times World Atlas, dating back to the 1950s, in its gazetteer, puts Smalls
    > Lt. Ho. at 51deg 43'
    > N, 5deg 30' W. That's about 6 miles SE of where Sumner shows it on his Plate
    > III which I estimate to
    > be about 51deg 48' N, 5deg 34' W. We really need an Admiralty chart of the
    > 1830s to resolve that
    > one, and I have no charts of that area to hand; it's away from my usual
    > cruising-ground.
    > The diagram in Bowditch puts the Smalls light at about 51deg 44' N, 5deg 30'
    > W, some 6 miles W of
    > its atlas position.
    > I suppose it's possible, but doubtful, that the lighthouse has migrated, from
    > one rock to another,
    > over the years. By the 1830s, longitudes of the more important headlands and
    > lights around the
    > British coast had been rather precisely surveyed, but really detailed surveys
    > did not happen in the
    > Irish sea until the 1840s, with small steam paddlers. Of course, charts were
    > not always updated
    > tquickly to correspond, and Sumner might well have been using an old chart
    > anyway.
    > Anyway, there seems to be some confusion about the matter, and if anyone has
    > access to old chart
    > information, they might be able to resolve it. I'll take a look in the
    > Bodleian Library, next visit
    > to Oxford.
    > The gazetteer of my Times Atlas gives the modern position of Tusker Rock Lt.Ho
    > at 52deg 12' N, 6deg
    > 12' W.
    > I wonder if that information helps Bill to put together his jigsaw.
    Yes, and thank you George.  The thought of migrating lighthouses gave me a
    good laugh.  I find your discovery/observations regarding the charts/plates
    extremely interesting.  As is so often the case, ewhen we answer one
    question, a new one pops up to take its place.

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