The Various Speeds of Lights in Inertial Frames of Reference

摘要

The speed of light in empty space was first measured by Roemer in 1676 who also found it faster on approach to its source and slower on recession. James Bradley in 1728 reported the speed of light incident vertically to be higher on approach and slower on recession. In 1881 and 1887 Albert Michelson showed that the speed of light did not change when both its source and observer moved forward uniformly on the same platform. These observations, often repeated, demonstrated that the motion of lights in inertial frame of reference varied according to the general laws of motion. However, erroneous interpretation of Michelson's experiments by Lorentz and FitzGerald lead to the notion that the speed of light was unaffected by the speed of its source or observer - it was a universal constant - later incorporated into Einstein's Theory of Relativity.