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Alex wrote-

| ...the thing that surprised me most
| at one was the mentioning of Capitan Edmund Halley, RN.
| It is amazing that this captain's name
| is exactly the same as of the
| great astronomer (and Newton's friend) Edmund Halley.
| I was so surprised that I even checked the biography
| of Edmund Halley (the astronomer). And of course it
| is very unloikely that this is the same person:-)

=========================

Response from George-

Alex's scepticism is misplaced. They are indeed one and the same. What was
the "biography" that  Alex claims to have checked? It must have been a VERY
incomplete one. I recommend he reads Ted's "Astronomical Minds", as an
antidote.

Halley had quite a lot of experience at sea, as Ted Gerrard's book would
tell him, and even better, a full Halley biography, of which the best is by
Alan Cook (1998).

At the age of 21 he spent a year in the South Atlantic island of St. Helena,
surveying the Southern skies. Presumably, his travel was as a passenger, in
a ship going to / from Cape Town.

At the age of 32, he had surveyed the Thames estuary , and presented his
results to the Royal Society. According to Gerrard, this went as far as the
Dutch coast, at the behest of the King, William III. At 35, he was running
salvage operations in the English Channel, of a treasure-laden vessel,
involving the first use of a diving bell.

But his main seagoing achievements were in those three voyages, from 1698 to
1701, in the Royal Navy vessel Paramore, a tiny pink of 89 tons, newly
constructed for the job with a complement of 20, for which he was appointed
Captain by the Navy. The first two, into the Atlantic, were to survey the
magnetic variation, mainly in a fruitless attempt to determine longitude by
that means (it was possible, but only in special circumstances, such as the
approach to the Cape of Good Hope). The third, a survey of the English
Channel, was to plot the tides and tidal streams, and the magnetic variation
too, in view of the many losses of vessels that were occurring in those
waters.

In those Atlantic surveys, Halley's main difficulty was not in measuring the
variation out in the ocean, but to know what his longitude was where he did
so. It didn't call for high precision, and Halley devised his own technique
for doing the job, a near-relation of the lunar distance method. He found
the position of the Moon with respect to the star background, in a way that
called for an intimate acquaintance with the stars near the ecliptic, that
only an astronomer would have. For navigational purposed, a longitude result
would be needed there and than, but Halley's need could be met by later
comparison with observed Moon positions, measured back in England, at the
same date. No method could work accurately on-the-spot without precise
prediction of just where the Moon would be. Halley spent most of his later
years working toward that goal.

In my own view, Halley's Atlantic voyages, made so early in the history of
longitude navigation, were in the first rank of navigational achievement,
and have never been properly appreciated. A full account from his journals
didn't appear until Thrower's Hakluyt edition of 1981. Halley is
frustratingly vague (or secretive) about his navigational techniques, and
Thrower's analysis of those is somewhat limited. Ted Gerrard's
investigations are the fullest that I'm aware of, but there is more detailed
work that ought to be done.

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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