Re: Dry "wet" roads

["John S. Denker" <jsd@MONMOUTH.COM>]

On 04/21/2003 07:48 PM, Bernard Cleyet wrote:
>  JD's site

I'm glad you like it, but it's not "my" site.
I just mentioned it.  I'm just the messenger.

> argues
> that all mirages are more properly refractions than internal reflection.

Wow, that's an interesting nicety.

In general, when a beam hits a change in the
index, there will be a reflected beam and a
transmitted beam.  One or the other of those
might be zero in special cases (Brewster's
angle or total internal reflection).

Reflection by metals is very similar to total
internal reflection in a refractive medium.
There is an evanescent wave that goes into the
metal.  It can be observed if the metal is thin
enough (gold leaf, half-silvered mirrors, ...).

I like to keep the word "reflection" around
because it is the counterpart to "transmitted"
and "incident".

I think it is safe to say that an odd number
of reflections produces a change in parity.
Unless somebody's got a better idea, I'm going
to take that as the defining property that
distinguishes the reflected beam from the
transmitted beam.

It doesn't seem particularly important whether
the ref**ction is caused by the refractive
properties of the media or by something else.
(Is there anything else???)

It also doesn't seem particularly important
whether there is a graded index or a relatively
sharp discontinuity in the index.  Typically
the evanescent wave extends quite a ways beyond
the nominal "boundary" even if there is a sharp
reflective boundary.