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From: gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>)
Newsgroups: net.physics
Subject: Re: Lightspeed
Message-ID: <5719@brl-tgr.ARPA>
Date: Sun, 11-Nov-84 15:49:44 EST
Article-I.D.: brl-tgr.5719
Posted: Sun Nov 11 15:49:44 1984
Date-Received: Tue, 13-Nov-84 01:19:50 EST
References: <683@hou2h.UUCP>
Organization: Ballistic Research Lab
Lines: 8

> ... if light does not propagate by 'disturbing' a
> medium, why does light travel at different speeds through different
> substances? (i.e., why does light refract through a lens or a prism
> and why do you get the illusion of a 'broken' pencil when you stick
> one in a glass of water?)

But light DOES interact with matter (electrons) if it's there.  It
need not be there for light to propagate, was the point.