Re: Bird's eyesight

Wasn't it Terry Harper who wrote:
>On Mon, 7 Nov 2005 10:29:09 +0000 (UTC), kgd@xxxxxxxxxxxx (Keith
>Dancey) wrote:
>
>>In article jgunm11i0e5s03b1m66a6ro6bcu4q8ubvu@xxxxxxx, Terry Harper
><terry.harper@xxxxxxxxxxxxxx> writes:
>
>>>When you can only see the reflection, it is a function of the
>>>refractive index of the glass, not your eyes. A bird will see the same
>>>as you do.
>
>>Not quite correct. The eyes of some birds are different from ours, and can
>>see the polarisation of light resulting from reflections from smoothe
>>surfaces; we cannot. Some can also see wavelengths that we cannot...
>
>It's not polarisation, it's total internal reflection. The effect is
>because of the way that light rays pass into and out of the glass.
>
>I'm sure that birds' eyes see things differently from the way that
>humans do, but they cannot see through a glass at angles above the
>critical one which gives total internal reflection.

That argument only holds true for high angles and for birds that are
actually embedded in the glass rather than on the other side of the
window.

The normal reflection from a window isn't total internal reflection,
it's specular reflection, and the light from that is polarised. Look at
the window through polarized sunglasses tilted 90 degrees and the
reflection will be considerable reduced. (Polarised sunglasses have the
polarization oriented so as to reduce the reflections off horizontal
surfaces.

--
Mike Williams
Gentleman of Leisure
.

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