> I just thought extinction was a formulae modelling the observations. of the > form A*e(exp(-Bx)) The solution of the differential equation for > extinction, you know....? That the loss of light per unit length is > proportional to the light intensity at that point.... > > Chris. It seems from a bit of research that the Extinction Theorem is not discredited quackery in itself but sadly it seems to be a favourite reference for pseudoscientists - like the one I quoted. The real theorem Dan referred to exists - though there seems to be no good explanation of it on line (you have to buy a book). I'm gonn try to look it up in Blackwell's on Sunday. In physics there are a lot of counter-intuitive thingumies. Are they real? Does it matter? In general the questions cannot be answered (are unanswerable) so are moot .... Bob