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    Re: The development of bubble sextants
    From: Douglas Denny
    Date: 2009 Aug 15, 06:47 -0700

    Agreed my use of Coriolis force is not good example for objects like a moving 
    shell in flight - moving relative to the rotating inertial frame of the Earth 
    when it is termed ficticious. Youare quite correct in fact.
    Mathematically it is nevertheless acting like a real force in calculation, 
    giving rise to (apparent) accelerations:-
    (Wikipeadia: "The Coriolis effect exists only when using a rotating reference 
    frame. In the rotating frame it behaves exactly like a real force (that is to 
    say, it causes acceleration and has real effects).
    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.
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