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George,

Still another informative article.  Hundreds more on the internet, but this
is the last one I'll send- promise.

http://www.ecsinc.com/library/2292.htm

Phil
----- Original Message -----
From: "George Huxtable" 
To: 
Sent: Friday, July 11, 2003 2:05 PM
Subject: Re: Arificial Horizons and Tea


> About Mercury artificial horizons, John Kabel wrote-
>
> >Mercury!! Were they kidding??  Bad enough in a barometer or
> >thermometer, where the glass is about as hazardous, but very bad in the
> >open.  I hope nobody is still using it, in this group.  A license to
> >die young.
>
> ===============================
>
> Can anyone supply any information as to the real level of hazard that
would
> be involved in using mercury in an artificial horizon outdoors?
>
> I suspect that it may be less lethal than John Kabel implies.
>
> I base this opinion on my childhood at school, where I sat for physics
> classes at a laboratory bench. Every hollow and cranny in the wooden
> surface of that bench would contain droplets of mercury. When the lesson
> became boring, we would do our best to fish them out with a pencil, to
> collect enough to coalesce into a blob that was big enough to flick at our
> friends in the row in front.
>
> Our reversing-switches would involve electrodes that dipped into open
pools
> of mercury, We would make barometers that dipped into similar open pools.
>
> Later, at university, we found a similar environment. We would use mercury
> in pint quantities for diffusion-pumps in high-vacuum systems.
>
> I suspect many physics students from my generation, the world over, could
> tell a similar story.
>
> Were we risking our lives? It didn't seems so at the time. I haven't
> collected mortality statistics. Were we risking brain damage? Perhaps
> that's starting to show, now...
>
> Now we have our teeth stuffed with amalgam. Does the amalgamation remove
> the toxicity? I wonder.
>
> Somehow I doubt that taking sextant altitudes by exposing for a short time
> a small pool of mercury, out in the open, where any vapour could blow
away,
> presents a comparable hazard. But I am quite prepared to be convinced
> otherwise, if any real evidence exists. Is John Kabel being over-alarmist
> about the danger? Am I being over-casual?
>
> In other respects, mercury must be the ideal artificial horizon. There's
> room for a simple design in plastic for a shallow pool with a sealing lid,
> from which the mercury would never need to be removed, with a rim intended
> to trap any overspill, designed with a tripod base. This would be handier
> than the equipment the old explorers had to handle, in which mercury had
to
> be transferred between a tray and an iron storage vessel with a screw-cap.
>
> But how available is mercury today? Are there regulations that prevent you
> and me from acquiring enough mercury to do the job? Do we have to collect
> antique barometers to do so?
>
> I'm not convinced about the virtues of floating a solid mirror on a
> disc-raft on liquid. The liquid and the solid would need to have a
> repulsive surface tension between them to ensure blobs wouldn't gather up
> the sides of the raft. That surface tension would require to be exactly
> even around the edges of the disc or the raft would be unbalanced. How
> would one prevent the raft from nearing the edges of the container, which
> would unbalance the surface-tension forces or give rise to friction which
> would constrain the self-levelling? There are serious problems here which
> would need resolving.
>
> George Huxtable.
>
>
> ================================================================
> contact George Huxtable by email at george@huxtable.u-net.com, by phone at
> 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
> Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
> ================================================================

   

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