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    Re: Bubble sextant instructions
    From: Capn MCL Rodaway
    Date: 2001 Dec 14, 7:43 PM

    Thanks for the info Clive & everyone else.  I have no plans for taking it
    with me out to sea, more for fun at the end of the pier.  They're just not
    as comfortable to handle as a proper sextant.
    
    Yours Aye
    Michael Rodaway
    
    Seamen, with their inherent sense of order, service, and discipline, should
    really be running the world.
    --Anonymous
    
    on 12/12/01 19:04, J.Sutherland at jcs{at}CWCOM.NET wrote:
    
    > Cap'n Rodaway;
    >
    > I have used the Mk9 sextant for many years. In its
    > unmodified form it is of
    > little use at sea as it is generally impossible to
    > keep the bubble steady
    > enough, although I confess I have never tried it
    > from the deck of a large ship.
    > If the steadyness of the vertical is tolerable,
    > then the vibration of the deck
    > caused by the engines can be an advantage.
    > These sextants are very old now and deterioration
    > of the glass surface on the
    > inside of the bubble chamber tends to make the
    > bubble stick (especially if it
    > is small) and the vibration helps in unsticking
    > it. Adjusting the bubble size
    > is a knack but it is surprising how many of these
    > sextants have retained their
    > liquid filling
    > War surplus sextants were frequently modified by
    > removing the bubble chamber
    > and adding a prism to arrange a simultaneous view
    > of the horizon. I have
    > modified (one of the earlier ones that didnt have
    > the averaging clock)  by
    > drilling a hole through the front and replacing
    > the 'horizon mirror' with a
    > split mirror (to produce the familiar arrangment),
    > while retaining the bubble
    > for use on land. The biggest problem with this
    > arrangement is that the glare
    > filters are in the combined light path and only a
    > strong horizon combined with
    > a weak Sun gives ideal sights.
    >
    > The sextant Mk IX with the clockwork averaging is
    > ideal for back yard
    > navigation and accuraces of less than + or - 1
    > minute can be achieved with
    > practice. Without mechanical averaging it will be
    > necessary to take up to a
    > dozen sights and average the result by graphing
    > the data.
    > The small bulbs for illuminating  the bubble and
    > the scales are very difficult
    > to find and even seriously damaged sextants should
    > be aquired if only to
    > caniballise  these bulbs.
    > Without them only Sun sights are possible
    > The web site below is what you are looking forif
    > it is still running. The
    > reproduction is poor quality but if you have any
    > trouble come back to me and I
    > will photo copy my booklet for you.
    >
    > Have fun!
    > Clive Sutherland
    > Abingdon UK
    >
    >> http://www.physics.uq.oz.au/physics_museum/bblsex.html
    >
    >
    >
    >
    > Cap'n MCL Rodaway wrote:
    >
    >> I was wondering if any one can point me to a web site or any other source
    >> for a instructions on using a WWII RAF Bubble Sextant Mark IX A.  Also what
    >> differences, if any, are there in working the sight with it, compared to a
    >> marine sextant?
    >>
    >> Yours Aye
    >> Michael Rodaway, M.N.
    

       
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