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Re: Cat's eyes



If I understand you correctly, John, you are saying that my
eyes reflected the kitchen light toward cat's eyes and then
the light was reflected back to me. I am not convinced that
this is a correct explanation. The orientation of my head would
be critical, but it was not. Cat was also not in a frozen position.

While quickly browsing Feynman's Chapter 35 I could not
find anything about this effect. Where does he discuss the
retroreflection of the eye? That word is not in the index.

I am familiar with the retroreflection in a corner cube. If cat's
eyes were corner cubes then they would always reflect light
back to a source regardless of cat's motion. My eyes, as you
implied (?) acted as a source. How could it be? The fixture
was on my right side (incidence angle close to 90 degrees).

Even if reflection from my eyes to cat's eyes were possible
the orientation of my head would be critical. but it was not.
Why do cat's eyes act as retroreflectors? Are there any
corner cubes inside of them?
Ludwik Kowalski

John Denker wrote:

At 11:29 PM 9/2/00 -0400, Ludwik Kowalski wrote:

The
impression is that light from the kitchen is somehow
"reflected" from my eyes toward the cat and causes
them to shine. Why do I see the shining cats eyes only
when my eyes are sidewise illuminated by the kitchen
light?

The phenomenon is so well known that the term "cat's eye" applies not just
to cats but any retroreflector. It is implemented in cats as a lens with a
mirror in the focal plane. (Trace a few rays for yourself to see how this
works.)

The only light that you will see retroreflected is light that comes from
your face (or from something near thereto as seen from the cat's point of
view). Anything that shades your face and/or blocks light coming from
behind your ear will cut down the retroreflected signal.

===============

As to why there's a mirror in the eyeball, see _The Feynman Lectures on
Physics_ volume 1 chapter 35. (BTW contrary to what RPF says on page 35-1,
the fovea is much smaller than the macula.)

A retroreflector can also be implemented as a corner cube.