Oops! In my last post I said that the impedence of free space was a measure
of the ratio of the amplitude of the magnetic field to the amplitude of
the electric field for EM waves propagating in a vacuum. I accidently
stated this quotient upside down. I should have said it was the ratio of
the electric field amplitude over the magnetic field amplitude (|E|/|H|
not |H|/|E|).