Tony Moss wrote:

>  Bob Haselby contributed
>
> >This sounds like a "signal mirror" which were also contained in life
> >jackets etc as survival gear. The more modern are quite effective
> >and are great for annoying people on the beach. It uses double internal
> >reflection in the hole to give a virtual image of the sun
>
> Any chance of a diagram or somesuch to show how this works Bob? - I
> understand 'total internal reflection' but 'double internal reflection"
> err!  yes!! err!!  I should have paid more attention in Physics instead
> of yearning for the workshop!
>
> Tony Moss

Tony,
I found a couple of web sites on signal mirrors.
http://www.equipped.com/signal.htm#ReflectionsOfLight
describes how they work and how to use them. I also made a sketch of how I
think it works. The attached bit
map file shows this. If you have any trouble viewing this let me know.
Bob


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