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Gary LaPook wrote, referring to Wright's longitudes for his zero meridian,
Cape Verde or the Cape Verde islands

This brings up the question of how were these longitudes determined by
Wright. If only by dead reckoning then it is truly amazing how
accurately they were determined. Anybody have any information about this?

Here, I am only guessing. All I have about Wright is what David Waters has
to say, in "The art of navigation in England in Elizabethan and early
Stuart.times" (1958). By the way, in plate 58, he shows the same chart of
the NE Atlantic as Gary has done.

Waters doesn't seem to say anything about his longitudes. But as I see it,
the best way of getting longitude, at Wright's date of 1599, would be to
find the local time of an eclipse of the Moon, a method which went right
back to Ptolemy. At night, my guess is that the local time could be
estimated using a nocturnal, based on the angle that the two guide-stars,
"The Guards", make with the horizon. It would be best if the same eclipse
had been observed back home, but otherwise, it would have to rely on
predictions. I doubt if any longitude could be determined to better than a
degree or two that way, but even so, that would be better than dead
reckoning.

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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