This movie simulates the set-up used in the Michelson-Morley experiment, including the non-existent aether wind they were trying to detect! The basic idea is to detect the time difference between light going "upstream then downstream" and light going "across shore and back."
Rotating the apparatus exchanges these two routes: you can rotate it by touch, or with a mouse.
The ratio of light speed to aether speed as portrayed here cannot (of course) be anywhere near 10,000, the order of magnitude M & M expected to find. To make our animation look more like the expected outcome of the original experiment, we have cheated by not taking into account the effect of the aether wind on the direction of motion of the light, but only including its effect on the speed of the light, the point of the animation being to illustrate the idea behind M & M's experiment, not to attempt a quantitative representation.