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Marcel Tschudin wrote-

| Frank you wrote:
| "But I suspect that Sadler's discussion of tides was just a
| speculation on his part --something that he hoped might explain away
| his unsuccessful experiments."
|
| I must say that I had exactly the same thought when reading George's
| question. It's difficult to guess now why those measurements led him
| to find the difference to what he thought they should be in the effect
| of tides. Or, did he just hesitate to analyse the data before cleaning
| them from tidal effects? I presume that those experiments were
| probably not "unsuccessful" may be only the interpretation of the
| data. It's a pity that people hesitate to publish their measurements
| even if they can't (yet) explain them or if they are still
| "contaminated" by other effects. This sort of data could possibly be
| useful to those who deal with refraction near the horizon. I would be
| interested in them if they still should be "sleeping" somewhere in an
| archive.

That seems possible. Some other matters that the NAO worked on were
written-up as internal reports, without publication. I've just asked the
department if there might exist some such report on their dip observations.
If those enquiries bear fruit, I'll let the list know.

And Frank wrote-

"Just consider that it can be low tide at one port a few hundred miles from
another where it's high tide.

"Are these effects, whatever they are due to, likely to be big enough to
affect dip observations?"

Maybe in some unusual areas with large tidal ranges (possibly inluding the
seas around Britain) you might want to worry about that at least
hypothetically."

In my local waters, around my home port of Poole, that's all too true. From
Poole, with its spring range of a couple of metres, a long days' sail at 5
knots can take you to Jersey, with a spring range of over 11 metres, and a
completely different phase.

George.

contact George Huxtable, now at george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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