Project the collimated beam of the projector
through the tank of water onto the screen. Stir a small amount of
cremora into the water. The suspended particles preferentially scatter
the light of shorter wavelengths, so that the beam seen through the sides
of the tank will start to appear blue, and the light that reaches the screen
turns yellow. Add more to make the water look bluer and the spot
redder. This models the effect of the atmosphere on sunlight.
One can use a polaroid filter to show that
the scattered light is partially polarized.
NOTES
Pine-sol also works to provide scattering
centers.
