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Although it's been a long time since I had the opportunity to look at
Edward Wright's table of the sun's declination, my recollection  is that
I was surprised, at the time, that the declinations were so accurate,
(after I figured out the calendar difference.) It was published a
hundred years earlier so these navigators should have been able to get
accurate latitudes. Anybody have access to that work to check the
accuracy of the declination of the sun for the period of the Shovel
disaster?

And thanks, Frank, for making that excerpt available, it was very
interesting reading.


gl


George Huxtable wrote:

>Frank wrote-
>
>| Here's a link to the file George provided:
>| http://fer3.com/arc/img/Clowdisley_Shovel_1707_JIN_1960.pdf
>|
>| For convenience, I also inserted a direct link at the end of the archive
>| copy of the previous message.
>|
>| Is this article under copyright? If so, please let me know in a couple of
>| weeks.
>
>=========================
>
>from George-
>
>Thank you Frank.
>
>I hope readers will take a serious look at it. It's a salutary tale of the
>dreadful state of Royal Navy navigation, in 1707. How things had changed by
>Cook's day, half a century later!
>
>Not entirely their own fault, of course. The concept of longitude, as a
>quantity that could be specified for locations around the world, with some
>common reference-point (perhaps at Greenwich), hadn't really sunk in then.
>Instead, mariners thought about changes in longitude, with reference to
>their starting point, derived from their dead-reckoning.
>
>But what I find so surprising are the discrepancies in latitude, in a fleet
>that was sailing together as a convoy. As long as the Sun shone at noon (and
>it had been doing so, reasonably often) latitude should have been clear-cut.
>Well, limited by the precision of their backstaffs, to perhaps 15 minutes or
>so.
>
>And not helped by the scandalous errors in charts, in the days when these
>were commercial ventures, before the Admiralty Chart existed. How many ships
>were lost because the Scillies, and Lizard, were plotted on the chart nearly
>10 miles North of their true position, I wonder?
>
>There's a decent gap, enshrined in the words of the old song, "Twixt Ushant
>and Scilly is thirty-five leagues ...", or 105 nautical miles. That was what
>mariners had to find their way between, and without even lighthouses, in
>early days. In the days before longitude could be measured, they had to do
>it by latitude sailing, taking deep soundings to establish how close in to
>the Western channel they had got. In thick weather, even latitudes were
>unavailable. That situation remained true, until radio aids became available
>(in the 1930s ?). I wonder if Henry Halboth can recall approaches made
>without even radio DF help, and how ships then managed, in prolonged thick
>weather?
>
>================================
>
>Frank asked about copyright-
>
>Yes, that paper is only 47 years old, so I suppose that copyright
>restrictions apply, strictly speaking, and I should really have pointed that
>out. Readers should respect that. It has here been made available for the
>purpose of academic discussion, but should not be disseminated further, and
>it might be wise for Frank to make it unavailable again after it's had time
>to serve its purpose.
>
>George.
>
>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 OX13 5HX, UK.
>
>
>
>
>
>>
>
>
>


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