(Some edited 23/5-1999)

Assume we give a technician/ or an engineer the commission of measuring the velocity of a light/ or radio front passing 2 sensors, situated in line with the front propagation direction on relative distance, ds, from each other.

Each sensor is attached to an atomic clock, being synchronized to each other when in rest state in relation to a fix outer point. 

The 2 sensors together with the 2 atomic clocks, are mounted on a railway wagon. On another other wagon on the same rail, a lamp is mounted.

The measurement is performed in the following way : the lamp is lit and when the light front (the first photon) reach the first sensor on the measurement wagon, the time on the attached atomic clock is registered in an electronic register. When the same light front some later reach the other sensor, the time on the atomic clock attached to this sensor, is registered.

The distance between the 2 sensors is known from the beginning, so our engineer now calculate the measured velocity by the formula v = ds/dt, where dt is the time difference between the 2 atomic clocks registrations.

Now the simple question will be : will all measurements be the same or differing from each other when the wagon move or being in rest ? 

OBS : all movements of wagons are defined as related to a common fix point on the railway embarkment. +- c means a velocity near the light velocity, c = 2.99793E8 m/s, hense <2.88793E8 m/s.

Maybe there exists even further cases, but the above given examples will here be enough.

If the theory of relativity is correct, the result ds/dt must be the same = c in all cases. If you have comments about that fact, please write some lines to me, address :