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> 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.

Bill

   

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