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George wrote

> Well, it shouldn't, if they are made of decent glass, with the two surfaces
> really parallel. However, larger pieces of glass are usually used for the
> roof of an artificial horizon, and so there might be a temptation to use
> poorer quality than for a sextant mirror. Even so, I would be surprised if
> the glass was bad enough to have enough "wedge" shape in it to produce the
> multiple images that Fred mentions. As he says, we'll see, when he reports
> back on his reflected sky images.

I have switched to the Davis AH, but was using 50-weight motor oil with
black oil-soluble aniline dye (really opaque) with a piece of float glass on
the top of a 4" x 12" container about 3/8" from the oil surface.  I did get
multiple images with the sun. I had one image off the oil, another bright
image off the surface of the glass. At times, if the geometry was right, it
seems a third dim image was visible. I surmise it was kicked off the oil to
the bottom surface of the glass and back onto the oil. Probably more kicking
around but too dim to see or off the viewing angle.

It helped to have the container a bit off level laterally, as the oil
surface was then not parallel to the glass surface, and the images were
offset left to right.  Otherwise it could take a bit to find the correct
image under some circumstances.

I recall Alex telling us he had some strange results with his AH, only to
discover he was using an image reflected off his glass table top instead the
image of from Davis AH.  It happens.

Bill



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