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    Re: The development of bubble sextants
    From: Paul Hirose
    Date: 2009 Aug 17, 15:45 -0700

    douglas.denny{at}btopenworld.com wrote:
    > This particular situation in discussion, however, of a sextant bubble held 
    by a person standing on the Earth, is an object tied to the Earth and the 
    "Coriolis" force here (i.e. the horizontal force due to rotation of the 
    Earth) will be real. My example of the North seeking gyro is more apt for it 
    is the (real) force which makes the North-seeking gyro work.  It was this 
    which I was thinking about. Sorry for the loose interpretation of Coriolis if 
    it caused confusion with the aircraft and bullets cases.
    
    Coriolis force doesn't affect a bubble level when it's stationary with
    respect to the ground. If it did, the eastward velocity due to Earth's
    rotation would force us to apply a Coriolis correction to convert a
    star's geocentric right ascension and declination to altitude and
    azimuth for a stationary observer. Of course no such correction is 
    necessary, even in precise work.
    
    Coriolis force doesn't make gyrotheodolites seek the meridian either. In
    fact, these devices work best at the equator (where Coriolis is zero)
    and become useless near the poles.
    
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