Re: ATM foucault test questions

["James W. Burrows" <burrjaw@earthlink.net>]

At 14:58 2002-12-10 -0500, wayne hilliard wrote:

>When doing the foucault test with a slitless moving source tester you have 
>your eye right up close to the knife edge.
>Wouldn't half the mirror be blocked by the knife and only half be visible?

Although there's more to the Foucault test than this explanation, think of 
a ray of light going out from the moving source, bouncing off a particular 
patch of the mirror, then going back toward the knife.  If that ray is 
blocked by the knife, the patch will look dark, if not, the ray will whack 
into your retina and your brain will say the patch is lighted.  Thank you, 
Leon Foucault.

         -- Jim Burrows
         --              mailto:burrjaw@earthlink.net
         --              http://home.earthlink.net/~burrjaw
         -- Seattle      N47.47233, W122.36620 (WGS84)