Jim_Cobb wrote: > Bob Haselby <[EMAIL PROTECTED]> wrote: > > Tony, 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 and so it is easy to hit what you are aiming at even though > > you are to far away to see the actual reflection on the opject that > > you are trying to hit. > > > Bob > > San Diego > > I believe "double internal reflection" must be the explanation I was > looking for. I'll have to give it some thought. I also remembered > another detail after I sent my last message; the annulus had a colored > portion, and I believe it was the colored portion that lent the color > to the indicator spot which I described (it's been thirty years since > I last saw this item... it's hard to recall all the details). I wish > I knew where to buy one of these gems so I could experiment... On > occasion I've looked in recreational equipment stores to no avail. > > Jim > ------------------- ---------------------- -------------------- > | Jim Cobb | 540 Arapeen Dr. #100 | [EMAIL PROTECTED] | > | Parametric | Salt Lake City, UT | (801)-588-4632 | > | Technology Corp. | 84108-1202 | Fax (801)-588-4650 | > ------------------- ---------------------- -------------------- > It's a good thing that we don't get all the government we pay for.
Jim, I found one of these signal mirrors in the surf years ago. The mirror was partially gone from the time it had been in the water. It was still in its flotation bag. In the diagram I showed the ring of reflective material (in mine it looks like a peice of screenwire with a hole in the middle and covered with little crystals. However even if your line of sight goes directly through the middle of the hole you still see a spot of where I believe the sun's image is backscattering off the surface imperfections in the glass. However it is not nearly so bright. The instructions on the back say to position the mirror so that the sun reflects on your hand or a nearby object, then without moving the mirror position your head and eye to look through the hole to see the suns reflection on that object. You will also see the light "ball" at that spot . Then move your head and the mirror together until the spot lines up with the distant object. As I recall you can almost knock a person off there feet at hundreds of yards away. Bob
