|MadSci Network: Earth Sciences|
When a car shines the headlamps onto fog, both refraction AND diffraction should take place. An observer standing inside the fog and looking at the headlamps will likely see a diffuse source. Depending on the angle of the observer to the source, and the size of the suspended droplets, they may also see a rainbow (look up rainbow angle). This is such an easy experiment, I highly recommend trying it next time you're standing in fog or in the clouds.
Try the links in the MadSci Library for more information on Earth Sciences.