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Gary LaPook wrote-

George, your post confused me because I had also checked Wright's
figures for the Cape Blanco case and came up in agreement with his
value. I think you may have read his text incorrectly because I read it
as giving the longitude of Cape Blanco as 331� and all of his longitudes
are east. This is where he plotted it on his diagram, 331� east which
is, as you point out, at 29� west of his prime meridian. This gives the
difference in longitude of 51� and using this value with the latitudes
of both places of 51� 32' north and using trig I come up with a distance
of 1864 NM just as you did and it is within 4 NM of Wright's calculation.


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

Sorry about that. Indeed, I had confused myself, in misreading a 
poorly-printed "1" as a half!. Gary is quite correct, that all longitudes 
that we would call Westerly were treated by Wright as Easterly, measured 
right round the Earth from his reference meridian. With a bit of thought, 
that should have been quite obvious. Istead, I jumped to confusions.

I presume (though may be wrong) that Wright didn't have the mathematical 
tools to check his great-circle distance, as we can do so easily now, in 
calculating cos (distance) from

sin lat sin dec + cos lat cos dec cos (longitude difference)

In which case, it is indeed remarkable that his geometrical constructions 
gave such close answers.

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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