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Alan wrote-

"In any event, re "leveling", if I remember correctly, I read somewhere
that this was NOT critical barring setting the thing up on a steep
hillside, as "water, I suppose ditto for oil and or mercury, seeks it's own
level". Is this, or is this not the case re using an artificial horizon?"

Yes, that's correct.

In guessing at how little Mercury one might be able to get away with, I
wrote, on 20 Jan-
"Mercury is VERY dense (over 13) so an ounce of the stuff won't go far;
occupying about 2 millilitres. My guess is that  around 10-15 ml would be
required in the trough of a sensibly-sized art. horizon, to make it easy to
use without having to be over-careful about levelling. That would
correspond to 5 to 8 ounces. Maybe it would be possible to penny-pinch and
get way with somewhat less."

Since then, Bill Morris has actually tried it out, to see how much Mercury
is required to get uniform coverage over the floor of an artificial
horizon, without the liquid gathering into blobs, and has assessed it as
750 grams. This is about 55ml, which is very much more than my own guess
that 10-15 ml might suffice. I've no doubt that he is right, and accept
that judgment. There's nothing like practical trial, to get a reliable
result.

And normally, the levelling of such an artificial horizon is very
non-critical, just as Alan says. It's only if skimping on the Mercury, that
any tilt might result in the liquid gathering in one part of the trough,
leaving another bare, or affected by meniscus.

Alan continued-

"I've done sun shots with mine, in the spring and summer, standing in a
reasonably level parking area at our apartment complex, taking sun sights
several hours apart, that when plotted show quite small displacement
between my calculated fix and  GPS coordinates."

This list thrives on numbers, Alan. Without numbers, even approximate ones,
a statement such as "show quite small displacement" has no meaning to
anyone other than you.

"Seems that orienting the ah properly is an important factor, as is being
able to stand far enough away from the ah so as to be able to see the
reflected and sextant suns."

That's a surprise, to me. On what basis do you deduce that any such
discrepancy is the result of mis-orientation? And why do you need to stand
back to see the two views? Surely, the closer you can get, the larger is
the solid angle that's available in the liquid reflector. I see no such
advantage in standing back, as long as the wind-shield isn't interfering
with the direct view.

George.

contact George Huxtable, at  george{at}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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