The Various Speeds of Lights in Inertial Frames of Reference

Harry H Mark

doi:10.11648/j.optics.20170601.13

Abstract

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.

Highlights

The speed of light in empty space was first measured by Roemer in 1676 who found it faster on approach to its source and slower on recession
By measuring the periods of Jupiter's satellites, Ole Roemer determined that the speed of light was higher when approaching and lower when receding from Jupiter than when at a steady distance from it
As noted above, the pencil will only travel farther forward when seen from a point outside the earth in reference to which it is at rest or moving, not from a position on it, where Michelson and the reader of his report were positioned

Summary

Introduction

The speed of light in empty space was first measured by Roemer in 1676 who found it faster on approach to its source and slower on recession. “On the hypothesis of a stationary ether it appeared possible to detect a motion of the earth independent of astronomical observations.” He trusted this fundamental possibility, the basis of the whole project, at the beginning of his 1881 paper copied here: “Assuming that the ether is at rest, the earth moving through it, the time required for light to pass from one point to another on the earth’s surface, would depend on the direction in which it travels.” (Figure 4) [8].

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