[Ringo]

aah, thats actually one of the explanations that I read. It's this line thats puzzling me, though..

"Light falling on the black side should be absorbed, while light falling on the silver side of the vanes should be reflected. The net result is that there is twice as much radiation pressure on the metal side as on the black. In that case the mill is turning the wrong way."

I know thats one of the older, wrong theories, but the idea of twice as much radiation pressure on the metal (reflected) side, as opposed to the black (where it is absorbed) puzzles me.