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Mirror Mirror on the Wall
I received this email from a friend.
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HOW TO DETECT A 2-WAY MIRROR
Police shows on television commonly use two way mirrors when they interrogate suspects. The police on one side of the mirror can watch the suspect, but the suspect can't see them. He merely sees a mirror hanging on the wall. How can you tell if a mirror is a two way mirror or an ordinarymirror? Just conduct this simple test:
Place the tip of your fingernail against the reflective surface and if there is a GAP between your fingernail and the image of the nail, then it is a GENUINE mirror. However, if your fingernail DIRECTLY TOUCHES the image of your nail, then BEWARE, for it is a
2-way
mirror! You can further ascertain the nature of the suspect surface by hurling an object (e.g. a chair!!!) at it. The chair will go through.
So remember, every time you see a mirror, do the "fingernail test". It doesn't cost you anything. It is simple to do.
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Will this test work?
Click to show the solution!
Solution
This will not tell you whether it is a two way mirror. Seeing a gap between your fingernail and its reflection tells you that you have a back surface mirror.
Most mirrors have a layer of glass in front and a silvered surface behind the glass. This protects the silvered surface from being scratched. The layer of glass causes a small gap to appear between your fingernail and its reflection.
Some mirrors have the silvered layer on the front. These mirrors are called front or first surface mirrors. The image quality may be slighlty better, but front surface mirrors are very
easily scrathced.