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    Re: Seeking advice for bubble repair on a Plath aircraft octant
    From: Ken Gebhart
    Date: 2009 Apr 6, 20:15 -0500

    I was waiting for someone else to weigh in on this.  Since Bill was
    not positive about the fluid, I might suggest a silicone fluid.  This
    is used on the older C. Plath bubble horizons that are adjustable.  I
    think there is more danger of xylene interacting with rubber-like
    parts that may be in there.  I have filled many C. Plath chambers by
    just spraying a silicone aerosol into a glass until it fills with
    enough fluid to inject into the chamber.
    Ken Gebhart
    On Apr 6, 2009, at 6:49 PM,  wrote:
    > Attached is a sectional drawing of the bubble unit of a Soviet IMS3
    > sextant. The instrument has many similarities to the SOLD, as the
    > latter was made by C Plath, whose satellite factories were over run
    > by the Soviet Army towards the end of WWII. The bubble units
    > appear, at least outwardly, to be identical.
    > 114 in the diagram appears to be the screw that, with washer 115,
    > closes the filling hole. The fluid was probably xylene or hexane,
    > rather than the alcohol solution or filtered kerosene used to fill
    > compasses. Xylene (or hexane in the UK Mk IX series) was chosen
    > because its refractive index is close to that of glass and so the
    > upper "glass" of the unit would not act as negative lens when the
    > chamber was filled.
    > The drawing has five pages of cyclostyled text in Russian referring
    > to it. I can scan and send these to anyone to whom they might be of
    > use or post them on my blog. Let me know what you would like.
    > >
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