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    Re: Making an artificial horizon
    From: George Huxtable
    Date: 2011 Jan 21, 00:16 -0000

    Jim Wilson wrote-
    | All this talk about mercury reminds me that the one hundred inch Mount
    | Wilson telescope is floated in mercury to minimize bearing loads. There's
    | not much of it, since a thin layer is all that's required. I thought the
    | idea ingenious.
    Yes, but not novel. It had been used for years in lighthouses, to support
    the heavy rotating lens/mirror assembly. The idea was to minimise the
    energy needed to drive it, which came from a falling weight, wound back up
    to the top of the tower at intervals, by hand. Also, to provide an
    effective draught-excluder in gale conditions.
    I imagine that in both examples, the flotation relieved the supporting
    bearing of most, but not all, of the load, so that the bearing still
    provided precise location of the rotating assembly.
    Perhaps it was the Mercury, rather than the isolation, which caused the
    dementia to which lighthouse-keepers were prone.
    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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