On Sat, 31 Mar 2007 03:35:47 GMT, Cecil Moore
wrote:

Keith Dysart wrote:
More curiousity: Can P1 and P2 have different signs, that is,
the power is going in different directions?

Please reference Chapter 9, Interference, in "Optics",
by Hecht, 4th edition. The two interfering waves are
traveling in the same direction. The associated
powers exist together at a point of interference.

It's a shame you have only one reference that is so impoverished as to
restrict itself to this "same direction." Otherwise, you would have
been able to answer Keith's question without asking him to figure out
what you couldn't. It is, after all, a commonplace of superposition
(that is what this thread is about, isn't it?) - or are you the
doubting Thomas this thread's subject alludes to?

The stumbling over absolute values was funny too. I was wondering who
was going to pull that rug.