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    Re: Artificial horizon
    From: George Huxtable
    Date: 2005 Feb 22, 00:02 +0000

    Marvin Sebourn wrote, about using large "engineering" spirit levels to
    adjust the plate of an artificial horizon-
    > .... If you  read my post, you
    >will see nothing suggesting that I used a level longer than 15  inches.
    >Your suggestion that there is an inherent uncertainty  of setup using larger
    >levels (because there removal might disturb the plate  alignment) is in error
    >because of the incorrect assumption that the  levels were removed after
    >alignment and prior to sighting use. They were  not, and they served to
    >indicate the
    >continued alignment of the  plate.
    >Were you "horrified" (that is, shocked, made fearful, or disgusted) by
    >considering the use of an eight inch spirit level? Really?
    Reply from George-
    I was certainly surprised that Marvin got that arrangement to work.
    Yes, if there's room on the plate to accept the continued presence of two
    such large spirit levels, at right angles, and still leave room for a
    reflected light path, then Marvin's argument holds water. But in that case,
    just how big did the plate have to be, and did it then allow use over a
    full range of altitudes and azimuths, without the light rays clanging on
    the spirit levels with which they have to share the surface of the plate?
    It would be interesting to know what the geometry was, and what
    restrictions, if any, it imposed.
    In general, artificial horizons were designed to be small, and therefore
    portable, to be used by explorers and travellers. Marvin may have had no
    such reason to restrict the size of his reflecting plate. I've no wish to
    get into a big argument with Marvin about this matter: with no portability
    limits on plate size, I accept that an arrangement such as he describes
    could be made to work.
    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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