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By Prof. Dayton C. Miller 1940

Beitrag aus dem GOM-Projekt: 2394 weitere kritische Veröffentlichungen
zur Ergänzung der Dokumentation Textversion 1.2 – 2004, Kapitel 4. 

The ether-drift experiment / Dayton C. Miller. In: Cleveland Plain Dealer. 1940, 10. März, "All feature section", S. 1 u. 6. Auch unter:
http://freespace.virgin.net/ch.thompson1/Papers/Miller40.htm

The Ether-Drift Experiment
By Prof. Dayton C. Miller (Cleveland Plain Dealer, 10 March 1940, "All Feature Section" p.1 & 6)

The wave theory of light received general acceptance in the 19th century, and this required the hypothesis of a luminiferous ether, filling all space, even that occupied by material bodies, through which bodies such as the sun and planets move freely without disturbing the other. Scientists sought to prove the existence of the ether by some direct experiment, and in 1878 Maxwell of Cambridge University, England, first proposed an optical experiment for this purpose. 

It is assumed that the ether as a whole is at rest, that light waves are propagated in the free ether in any direction and always with the same velocity. The experiment is based upon the argument that if the speed of light were determined by an observer on the moving earth, the apparent speed would be different according to whether the observer is moving in the line which the light is travelling or at right angles to this line. The detection of such an effect, would be accepted as proof of the existence of the ether. 
An incomplete analogy is given by a power boat on a river, the speed of which would be different when sailing down stream from the speed with the same power when sailing across the stream. Not only would the speed across stream be slower, but in order to reach a point directly opposite the starting point, the boat would have to be headed somewhat upstream. 
The late Prof. A.A. Michelson accepted the challenge of Maxwell’s suggestion, and in 1881 devised the remarkable instrument called the interferometer, by means of which it is possible to compare the speed of a beam of light which travels in the line of motion of the earth in space, directly with the speed of a beam at right angles to this motion, by detecting the difference in the two speeds. In the interferometer a beam of light is literally split in two by a "half-silvered" mirror, and the two beams may be made to travel paths at right angles to each other. At the end of the desired path, each beam is reflected back upon itself and the two come together where they first separated. 
If the two beams travel equal paths with equal speeds, the reunited beams of light will blend with the waves of concordance. If, however, the speeds are different in the two paths, the two beams come together with differences in the phases of the waves, producing effects which are observed as the "interference fringes". 
The interferometer enables one to detect exceedingly small differences in the relative speeds of the light in the two paths, the measurements being made in terms of the wave lengths of light. Michelson’s first apparatus proved inadequate as to sensitivity and stability. 
He came to Case School of Applied Science in 1882 as the first professor of physics, and became associated with Prof. Edward W. Morley of Western Reserve University. Prof. Morley proposed several important developments in the interferometer. The light path was increased in lengthy by multiple reflections, and the optical parts were mounted on a stone block five feet square and one foot thick. The stone was floated on a large basin of mercury so that it could be easily rotated to bring one of the light paths of the interferometer into line with the earth’s movement in space. 
With this instrument, the famous "Michelson-Morley Ether-Drift Experiment" was performed in Cleveland, in July 1887. Again the results were inconclusive and the instrument was of insufficient sensitivity for the delicate measurements.

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