NavList:

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