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    Re: Arificial Horizons and Tea
    From: Robert Eno
    Date: 2003 Jul 11, 19:45 -0400

    Eno responds,
    My job, among other things, involves the management and disposal of
    hazardous waste. Mercury is right up there with the nasties; worse than PCBs
    and worse than many other substances. Very useful stuff but hazardous when
    I can't cite the literature but some time ago, there was a study conducted
    on the health of chemistry teachers and anyone else who spent most of their
    working days in chemistry labs. It was found that these professions had much
    higher incidences of minimata disease -- essentially, short circuiting of
    the nervous system -- and that this was caused by the slow volatilization of
    mercury trapped in the sink drains and cracks in the floor. Most students,
    when confronted with broken thermometers, would simply hide their sins by
    flushing the mercury down the drain (guilty as charged), after which it
    would remain in the sink trap and slowly poison the lab teacher.
    Mercury is not to be trifled with. In fact it should be avoided. The more
    you handle it, the more long term risks you take with your health. Stay
    clear of it. It is simply not worth the risk when there are far superior
    artificial horizons available.
    I have used them all: mercury, water, oil, etc. etc. and my vote is for the
    flat black glass artificial horizon. That it is not self-leveling like
    mercury or tea, is merely an inconvenience; not a serious impediment to
    accurate position fixing. I much prefer a glass horizon. Mercury, tea, oil
    and other liquids are simply a pain in the a---. Actually, I prefer a bubble
    horizon. The old C.Plath is the best ever.
    As for mercury amalgams, the jury is not out yet. There are many conflicting
    reports and opinions, however, the overall consensus -- based on data from
    the millions of unwitting guinea pigs (like me) -- seems to be that the
    mercury amalgams in our fillings do not present a serious risk. They have
    been used for close to a hundred years and there does not seem to be any
    evidence of damage to the nervous systems of people with bad teeth.
    My two bits' worth.
    Robert Eno
    > 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
    > 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
    > 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
    > 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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