Der Gerechte geht heim, doch sein Licht bleibt.

Light Speed Measurement

The basic principle

Rotating Mirror Method from Jean Bernard Léon Foucault



Here you can see the bundled beam of light which hits the semi permeable mirror. It split into two beams. The first beam goes down vertically and becomes a point on the scale.

The second beam hits the rotating hexagonal mirror. There it is reflected and thrown back by another mirror.

Meanwhile the hexagonal mirror has rotated a little bit. Because of that, the second beam is sent into the objective in another angle. So it goes down vertically. Thereby the second point is on another place then the first one.

Then the speed of light can be worked out by the distance between two points, the given ways and the speed of the motor.