From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


Hi
 Also, as I mentioned before, twilight sky is quite polarized.
I suspect it would work for many applications that require a polarized source.
Dwight

>From: "Bob May" 
>
>Arthur, if you cross a pair of polarizers, the light going through the
>polarizers gets real dim and usually turns a purplish color.  If you can't
>do that, you don't have polarizers.
>The source of the light is irrelevant as this is a function of the
>polarizers themselves.  I'll note taht polarized light will need only one of
>the polarizers to get this condition to some degree, depending upon the
>level of the polarization of the light source.
>What happens with a piece of glass between is that it modifies the
>polarization by rotation to some degree or another and that rotation is what
>you are going to see as different parts of the glass will rotate the light
>to differing degrees if it is stressed and that makes a difference in the
>brightness of that area of the glass.  Thus you get to see where the
>stresses are in the glass by a very simple method.
>Many descriptions of tests on the list lately, including mine, are specific
>versions which try to use the reflection at a large angle to produce the
>polarized light so that the tester can use simple, very available sunglasses
>to complete the necessary optics to do the complete test.
>Bob May
>http://nav.to/bobmay
>bobmay{at}nethere.com
>NEW! http://bobmay.astronomy.net
>
>
>
>

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