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    Re: Ebay kollsman periscope sextants
    From: Noell Wilson
    Date: 2018 Jun 9, 09:56 -0700

    Mercury didn’t work well for me as a substitute “bubble”. Stiction WAS a problem. I estimate that I could tilt the bubble housing several degrees without moving the stationary ball of mercury.

    Looking at the sun, I’d guess that the mercury was about 1/10 of the total view. I could tilt the sextant and move the sun the width of the mercury without the mercury ball moving at all.

    I used an old A-10 housing with the lens reversed so the ball of mercury was on the bottom resting on the concave surface. I didn’t use any dampening fluid. After getting stiction with the first try, I cleaned the inside of the chamber and waxed and polished the concave lens surface with some auto paste wax. No science there. It just seemed reasonable.

    I used mercury in a small plastic squeeze bottle. I covered the outlet and inverted the bottle to let any trash float up. I released a bit of mercury into the bubble housing and used a small hypodermic to reduce the bubble size to about 1/8”. The mercury ball surface looked very clean.

    The motion of the mercury on the bottom of the bubble housing is opposite to that of a bubble. Tilting left makes the mercury move left - downhill. Perhaps using a bubble previously made this seem backwards to me.

    Pity. Mercury would seem to make a good “forever” bubble - if it worked well.
    Regards, Noell

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