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During one of my "basic survival at sea"-courses I worked with a square 
signalling mirror that had a sort of handle with a string attached to 
it. That handle had a small hole in it, just like the mirror on one of 
the corners. The mirror also had a number of concentric circles around 
that hole. The mirror and handle were connected with a piece of string 
of about 25 centimetres that ran through those two holes. The whole idea 
was to look through the hole in the mirror and through the hole in the 
handle (the handle being further away from your face than the mirror) to 
the object that needed your attention, then cast a projection of the 
concentric circles on the hole in the handle. The string would help to 
stabilize the whole set-up. This would then result in the reflected 
light to be cast in the proper direction. It works about the same as 
shining the light through the fingers of your other hand while pointing 
in the proper direction as can be seen in attached images (The amount of 
fingers to be used might vary on the country where you're in ;-)).

Nicolàs



Bill Noyce wrote:
>> Every French yacht is
>> required to carry a signalling mirror. It is just a plain round mirror about
>> 12 - 15 cm in diameter with a hole in the middle. You turn in the direction
>> of the sun and look through the hole. You then see a red point which marks
>> the spot where you are just reflecting the sun rays.
>>     
>
> The sun shines through the hole and makes a small spot somewhere on
> your face, usually, and the back of the mirror is also silvered.  If
> you move the mirror so the spot on your face is imaged at the hole,
> then the front of the mirror is shining at whatever you see through
> the hole.  I assume that's the mechanism behind the "red point"
> Wolfgang mentions.  You need to be able to tell where your target is,
> but you don't have to see the light shining on it.
>     -- Bill
>
> >
>
>
>   


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