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    Re: Arificial Horizons and Tea
    From: Phil Guerra
    Date: 2003 Jul 11, 17:14 -0500

    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---.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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