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    Re: The development of bubble sextants
    From: George Huxtable
    Date: 2009 Aug 21, 16:39 +0100

    I suggest that Hanno curbs his enthusiasm for copying a Bush horizontal
    mirror for a bit, while he ponders on some of its snags.
    A hard look at the patent specifications, (1912358), might perturb him, as
    it perturbs me.
    Just setting to one side the question of its dynamic performance to changes
    in tilt and acceleration, consider only its static behaviour, after it has
    been sitting in a steady position for as long as necessary for everything to
    have settled. The aim is to end up with the mirror, #59, accurately
    horizontal. How is that to be achieved?
    I refer to components as numbered in the three diagrams that form part of
    the patent . The assembly #51, to which the mirror is rigidly coupled,
    appears not to have any pendulous property in itself. There's no
    ballast-weight to tell it which way is up. Instead, it appears to take its
    sensing of the horizontal entirely from its coupling with the spherical
    container #35, within in which it sits. For the purposes of this argument,
    we will assume that somehow #35 has managed to make its own equator exactly
    horizontal, because of the way it's ballasted and floating on Mercury. How
    does #51 then contrive to follow it? Only by means of its coupling of four
    light springs #53, connected very close to the centre of the triangular
    assembly #52.
    That angular coupling has deliberately been made flexibly weak (for
    dynamical reasons), just where (for statical reasons) it needs to be firm
    and precise. Remember, any tilt of the mirror from the horizontal, of more
    than a very few arc-minutes, would devalue the instrument for its intended
    Hanno should contemplate, hard, how he would actually implement that
    mechanical arrangement to ensure that the mirror-plane corresponds precisely
    to the equator-plane of #35, especially in the absence of any
    fine-adjustments, which are nowhere to be seen.
    The whole notion is impractical and flawed, which presumably explains why it
    was not made. I hope my words will save Hanno from much wasted effort.
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "Hanno Ix" 
    Sent: Thursday, August 20, 2009 4:34 PM
    Subject: [NavList 9574] Re: The development of bubble sextants
    I also like making things, and making them well. A usable gyro, mechanic or
    otherwise, would exceed my capabilities by far, a bubble spirit - even a
    DoubbleBubble - would not. And I would be thrilled if I could build a bubble
    spirit that is significantly more stable than the ones known sofar -- no
    matter the practical use.
    As far as practical navigation: gyros have such superior properties which
    never could be matched by any bubble spirit. They can seek North for once, a
    spirit level never could.
    Do I sense, though, that you have come to agree with the concepts of Bush's
    I'd be delighted.
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