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Subject: Re: Sextant Accuracy and anomalous dip
From: Bruce Stark (Stark4677@XXX.XXX)
Date: Wed Mar 19 2003 - 14:20:39 EST
Even if a boat could be made as steady as a lighthouse foundation, altitudes
taken from it would not be as reliable as those taken from a ship. Or so it
seems to me. I believe that the nearer the navigator's eye is to the water,
the more anomalous refraction will displace the horizon.
To simplify the logic behind this idea, forget about normal refraction.
Suppose that under normal conditions light would come to your eye from the
horizon in a straight line. To simplify things further, suppose anomalous
refraction occurs at a particular point along the line, making an angle at
that point. So the navigator will see the horizon at that point, rather than
at its true place.
Air near the water is the main breeding ground of anomalous refraction in the
dip. A navigator on the bridge of a ship will be a long way from the point
where anomalous refraction has bent the line. The angle at his eye, between
the true horizon and the point where he sees it, will be small.
A navigator on a small boat, on the other hand, will be close to that point.
Consequently the angle at his eye, between the true horizon and the point
where he sees it, will be larger.
I hope List members will overlook the simplistic way this is presented and
examine the question in their own minds, as well as in the light of
experience.
Bruce
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