On Apr 9, 12:20 pm, Roy Lewallen wrote:
Jim Kelley wrote:

I think we both understand that light travels at a velocity which is
dependent on the medium through which it is travelling. You seem to
want to continue to argue about that, and to tell you the truth I can't
see much difference between that, and the kind of debate going on over
and over in this newsgroup.

This isn't the first time I've failed to communicate, and I'm sure it
won't be the last.

The sole point I was trying to make is that the letter c is just about
universally used, as far as I can tell, to mean the velocity of light in
a vacuum. That symbol is not generally used to mean the speed of light
in any other medium.

Roy Lewallen


I'm with Roy on this. v is a wonderful symbol for generalized
velocity; c is used by far too many--as Roy says, almost universally--
as the velocity of light in vacuum. Speaking of failures to
communicate, I think using a symbol that's so well accepted to mean
one thing when you mean something else is a wonderful way to
precipitate failures of communication. Clear communication is aided
by not changing the meaning of well-accepted symbols.

"Let's see... e=m*c^2. Now what c is that? Is it 3e8m/s, or is it
only 3.4e7m/s because I'm in water? Will the nuclear blast be only
1/78 as energetic because it's conducted in water? Oh, but wait, at
higher frequencies c is greater than at low frequencies, in water.
Oh, I'm getting soooo confused...." No, c=3e8m/s, nominally.

"Let's see... epsilon-zero = 1/(mu-zero * c^2). Now what c is
that? ...."

Examples of equations where c is taken for granted as the freespace
speed of light abound. I think publishing an equation where c is the
speed of light, but not necessarily the freespace speed, shows poor
technical editing.



Cheers,
Tom