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    Re: Bubble sextants on e-bay
    From: Douglas Denny
    Date: 2009 Jun 6, 15:35 -0700

    The Fairchild has a thin lead washer of lead wire in a circle and crossed-over 
    at the join - underneath the glass lens, acting as a maleable seating; with a 
    thin brass shim washer on top pressed down by the slotted screw ring.
    Squashing the lead it with the glass lens under pressure makes the seal. 
    The link has the glass lens (which has a tapered edge uppermost) sitting in a 
    seating with some shellac or other material which has become a hardened 
    brittle material on the glass edge in the seating;  and a large, thick lead 
    washer on top which is compressed by the slotted ring into the tapered glass 
    lend edge and threads.  It seems Link did not want any leakage under any 
    circumstances as they went in for overkill here.
    The lead washer had to be cut away as it had become squeezed into the space of 
    the tapered glasss lens and thread area.  Hydraulically pushing it out with 
    pressure from inside is clearly the best option.
    Will do that next time I come across one.
    Douglas Denny.
    Chichester. England.
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