On Tue, 12 Jul 2005 22:48:00 -0500, Cecil Moore
wrote:

Nor will we find a
negative scalar quantity accompanied by the claim that the negative sign
indicates a change in direction, as you have done.

On the contrary, in equation 9.16 above, according to Hecht, the
interference term is negative indicating "total destructive
interference", his words, not mine. Here's Hecht's quote from _Optics_.

[Hecht rolls his eyes] Jim's point is won, absolutely nothing quoted
here explicitly states a change in direction. That is, as Jim points
out, the math follows the physics, it does not create the physics.
There is a vast gulf between being descriptive and being proscriptive.