In sci.physics Ken Muldrew wrote:
Ian Stirling wrote:

In sci.physics Ken Muldrew wrote:

When using a sextant on land (an odd thing to do nowadays since they
cost far more than a gps unit) one uses an artificial horizon in place
of the sea horizon. This is a small pool of water or mercury with a
couple of pieces of glass arranged in an A frame overtop to keep the
wind from disturbing the liquid. Water doesn't reflect very well and
mercury is hard to get these days (and hard to keep clean as well) so
it's tough to do star sights. Does anyone know of a liquid (or
something to form a film on top of a liquid) that might do better than
a simple pool of water?

Indium/gallium/tin eutectic melts around 10.7C.
Probably not much use.

Yeah, I think mercury would be much better. On the other hand, I
wonder if one could obtain a plastic that is light enough to float on
water with perfectly parallel sides and just silver the top. That
might do the trick.

Polarising films might boost the reflection a bit, I suppose. (well,
cut down on irritating reflections.
Na/K will be easily molten enough.
You'd need to put it in a sealed vial, with an inert atmosphere, as otherwise
it'll burst into flame.
(Hmm, maybe self-illumination could be a feature.)