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This piece, from the very first issue of Philosophical Transactions (1665)
vol 1, pages 13-15, has some navigational interest.

Some notes-

"Major Holmes" is better known as Captain Robert Holmes, later Sir Robert.

His destination, rather badly printed on line 3, was Guinea, on the coast of
Africa. His voyage, with a small fleet, was a Royal-sponsored adventure, to
break the profitable slave-trade monopoly of the Dutch, for the benefit of
the newly-formed "Company of Royal Adventurers Trading into Africa". (See
Ted Gerrard's book "Astronomival Minds".) It worked, for a year, until the
Dutch restored the status quo.

"The Isle of St Thomas under the line" was Sao Tomas, at about zero degrees
latitude (hence "under the line") and about 6 degrees 30' East of Greenwich
(though Holmes was unlikely to know that). "Adjusting his watches" there
implied that any longitude changes would be relative to the longitude of Sao
Tomas, whatever that was worth..

Going homeward, Holmes' enormous diversion, to the West, made sense, in
taking advantage of the circulation pattern, as the Portuguese had
discovered. Even to modern times, the sailing-ship route from the East to
the English Channel followed a mid-Atlantic track, . Sailing Northwestward
from Guinea through the Bight of Benin was unprofitable.

If his pilots were proposing to touch at Barbados for water, when no more
than a day's sail from the Cape Verdes, their notions of longitude must have
been way adrift. It didn't call for much precision, from a timepiece, to do
better than that. But Holmes' good experience, with Huyghens' marine
timekeepers, was not replicated by others.

One great problem, with pendulum timekeepers at sea, was the difficulty of
simply keeping them going at all, in rough weather. Perhaps that was the
main reason for carrying two, in the hope that if one stopped, the other
might carry on. But even if all the problems of ship's motion had been
resolved, a pendulum would never make a good timekeeper for ocean travel,
subject as it is to the variations in gravity. It would be another century,
after abandonment of the pendulum, before Harrison came up with a dependable
marine timekeeper.

Holmes made the most of his stop for water by seizing the Cape Verde Islands
for England, another claim which would be reversed before long. Holmes had a
talent for stirring up trouble, and his actions were a trigger for the
Second Dutch War.

Huyghens' references to the "States" presumably refer to the United
Provinces of the Netherlands.

A good article on "The Longitude Timekeepers of Christiaan Huygens" by J H
Leopold, is on pages 102-114 of that superb volume "The Quest for
Longitude", ed. W. Andrewes, (1996).

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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