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    Re: Old Sextant on German money
    From: Wolfgang Köberer
    Date: 2007 Mar 11, 10:16 +0100
     Frank's suggestion
     
    If you want to signal someone several miles away with a mirror, how do you get the angle right if you don't happen to have a Gaussian heliotrope in your survival kit? Here's a simple method: Drive a stake in the ground with a nice point at the top to serve as a sight. Step back ten feet from it and hold the mirror in front of you so that you can look just over the top of it at your target lined up directly behind the point at the top of the stake --your eye, the mirror, the point of the stake, and the distant target are now all lying on one line. Roll the mirror around until the beam of sunlight reflected from it just strikes the top of the stake. If you can maintain the pointing within about an inch at the distance of the stake, then you can be assured that your beam is reaching its target, since an inch at ten feet is about half a degree. Flick the mirror up and down so the projected beam shifts six inches along the stake, and you're all set to send code:
     
    works on land. But what about signalling like that from a boat?
     
    Our French friends obviously have a solution for that: 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. We've tried it sailing down the Cote d'Azur when we had nothing else to do and it works fine: the person that is in the red spot sees a bright flash of sunlight. I can imagine though that  when you're really in distress on a small yacht the sun isn't shining - or the direction where you want to send your signal is not towards the sun - or the boat is tossing you around too much. That may be the reason why this gadget never made it to the survival kits in Northern Europe.
     
    Regards,
    Wolfgang

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