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Gary LaPook wrote-

| 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?

Gary is, I think, referring here to Edward Wright's "Certaine errors in
navigation ...", published in 1599, which contained a table of the Sun's
declination. However,  that was preceded by William Bourne, in "A regiment
for the sea" (1574). Bourne predicted Sun declinations, for noon at London,
for every day over a four-year cycle, 1573 to 1576. This repeated, rather
precisely, over each leap-year cycle, so it could be used over a number of
such cycles. It was designed to be highly usable, giving declinations in
simple terms of degrees and minutes. I haven't seen an analysis of its
precision, but am pretty sure it was far more accurate than altitudes could
be measured in that period, by cross-staff and, later, backstaff.

Bourne's work was largely based on Cortes' "Arte de navegar", and
declinations had been available, for many years before, to Spanish and
Portuguese navigators.

I doubt if any errors in latitudes of vessels, in the Shovell disaster of
1707, could be attributed to defects in Sun declination predictions.

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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