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Tony Crowley wrote (inter alia)

> 3. David Origamus was the author of an ephemeris for the years 1595 until
> 1650 and based on the meridian at Wittenberg. Later in his journal, Baffin
> uses both Origamus and Searle with similar results and refers to a 17
> degrees difference in longitude between London and Wittenberg.

Interesting. If the Wittenburg is the one I think it is, that's only about
12 degrees East of London, so that would throw out any calculated longitudes
from London that were based on a Wittenburg ephemeris.

> 5. Baffin generally used a 4 feet semi-diameter quadrant to measure the
> suns
> altitude.

Ah yes, Tony had mentioned that quadrant before, and I had forgotten. That
was an astronomer's instrument, not a navigator's. Clearly, Baffin was more
than a simple mariner.  I had suggested he might use a cross-staff or
backstaff, but a quadrant, fixed on land, would allow Sun altitude to be
determined much more precisely, without needing a view of the horizon.
Especially one so large as 4-feet radius, which would allow rather accurate
measurements around the arc, if it had been divided accurately. Two
limitations should be kept in mind, however.

1. It was in the days before telescopes had been applied to such
instruments, so an observation was no better than the naked-eye could see
through peep-sights without magnification.

2. It required accurate levelling, presumably with a plumb-bob. This would
have been difficult, out in the open, except in very still weather.

Nevertheless, Sun altitudes within a few arc-minutes should have been
achievable.

Tony didn't give a reference for the information he quotes.  I, for one,
would be keen to follow it up, having become interested in Baffin. More
details, please.

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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