No, I see what you mean, but what that means is that the refractive index changes for light of different frequencies just like different frequencies of radio waves are affected differently in the atmosphere, eg. HF radio "skips" off the ionosphere and VHF radio is really only good up to about 5-10km line of sight.
I know I am drawing a pretty long bow when I compare light to radio frequencies like that but what I am getting at is that different frequencies are refracted differently in the medium, just like 1900Mhz doesnt like going through rolls of bubble wrap (happens to me at work using cordless DECT phones)
Have we slipped off topic?
ummm, now I cant sleep!
Chris
