The mind of AA Michelson was focused on using his understanding of measurements involving light to probe the world of physics. At this time it was the view that energy such as light needed a ‘lumiferous aether’ on which to travel – much in the way that sound waves need physical atoms. This ‘lumiferous aether’ was considered to fill all space, with all physical objects – such a planets – making transit through its substance. One of the issues of deep speculation related to determining the relative speed of the earth to the ‘lumiferous aether’.
The Luminiferous Aether: the Work of AA Michelson
Already experiments had been undertaken by other investigators, which had not detected any effects. Michelson began to speculate about how he could develop significantly better measurement techniques. There was no doubting that success in such a venture would be a pivotal achievement. Michelson resolved, however, that he needed to expand his scientific knowledge and accordingly enrolled late in 1880 at the University of Berlin where he attended the lectures in theoretical physics of Professor Herman von Helmholtz.
Thanks to a grant from Alexander Graham Bell whose interest had been aroused, Michelson was also able to make progress with a measurement system to detect the speed of the ether. Initially, his apparatus was referred to as an ‘interferential refractometer;’ in later years such equipment would be described by the more familiar term of ‘interferometer’.
It became apparent that the mechanical stability of the measurement system required was almost impossible to achieve within the busy city of Berlin. The developing apparatus was transported to the site of a new astronomical observatory being constructed in Potsdam - around 15 miles from Berlin. The mechanism was so sensitive that the process of stamping on the ground some 100 metres away would cause the interference fringes to vanish. The development of the experiment, however, was not without its cost in human terms. Michelson during this period of intense development saw very little of his wife Margaret.
The outcome of the experiment appeared to be negative. As the apparatus was rotated, the relative movement of the fringes that Michelson could measure was around 8/100 of the distance between adjacent fringes. This was comparable to the expected difference associated with the potential movement of the ether. In practice, however, the change observed was about 1/100 of the distance between adjacent fringes. There can be no denying that the process of making repeated measurements would have been a thoroughly demanding exploit. Subsequently while attending classes given by Robert Wilhelm Bunsen,at the University of Heidlberg, Michelson became aware of the ability of elements to radiate characteristic spectra.
An American in Paris
While in Europe, Michelson was able to spend some time in Paris – highly regarded at this time as a centre of the developing science of optics. After Michelson successfully demonstrated the fringes of his interferometer system, a former pupil of Cornu was able to indicate that the relative fringe shift expected in the ether drift experiment was not in fact 0.08 but instead 0.04 of a fringe.
Being separated from Michelson at this time due to the birth of their daughter Elsa, his wife began to feel resentment at their lack of time together. Eventually, however, suitable living quarters were found for his expanded family. It was with immense relief that Michelson learned in the spring of 1881 that he had received the offer of an appointment at a University in the USA – at the recently founded Case School of Applied Science in Cleveland.
Back in the USA
The scale of the organisation at Case, however, was remarkably modest - five faculty members and a student body of seventeen. Michelson used his knowledge of the state of science in Europe at this time to order a range of specialist optical equipment items. Also, with funding from the trustees, he acquired equipment to repeat his speed of light estimations. At this time Micheson was engaged in teaching students as well as undertaking his own research. His observations in Potsdam, however, did not feature in the lectures he conducted, though he continued to give the focus of the ether drift experiment, intense mental scrutiny.
Michelson was soon able to continue his researching into light – and in particular in setting about making new determinations of the speed of light. His stay in Europe had allowed him to establish contacts with some of the world’s best producers of optical systems and components and funds were allocated to him to purchase a range of such equipment. A sequence of new determinations made around 1882 established a value for the speed of light that would remain the accepted standard until Michelson made additional measurements between Mount Wilson and Mount San Antonio in California in 1927.
This was a period where Michelson had a direct input to student teaching where it was noted that his lectures were ‘most elegant, absolutely clear and finished’. Although his experiments in Berlin of 1881 were not part of his lecture material, Michelson continued to speculate about changes in experimental technique that could allow a positive result in the case of the ether drift experiment.
Scientific Highs and Personal Lows
It was a landmark meeting of the British Association of the Advancement of Science in 1884 in Montreal that gave Michelson an opportunity to learn at first hand from the like of Lord Rayleigh and Lord Kelvin about current perception on the key issues of science. Later Lord Kelvin delivered a separate series of lectures in Baltimore that left a lasting impression on those who heard them. It was in this latter forum that Michelson met Morelely, a research chemist, and discussed plans to try to detect changes to the speed of light in water traveling in a waveguide.
Before these plans could be developed, however, Michelson’s health failed due to overwork and he was unable to work between September and December of 1885. During this time, a ‘replacement’ had been found for his teaching position in the faculty at Case and the gulf between himself and his wife Margaret widened considerably although the marriage lasted another thirteen years. More withdrawn as an individual, his means of coping with the world at large was to place even greater effort into this research work.
A serious fire in October of 1876 effectively destroyed the laboratory facilities and Michelson had to spend future months reconstructing his experiments in Morley’s laboratory. The gloom was somewhat lifted when Lord Rayleigh suggested that it was time that Michelson’s ether experiment in Potsdam was repeated. This gave impetus to Michelson and Morley to set about constructing a specialist interferometer to try to detect the ether drift effect.
The Cleveland interferometer exhibited some significant enhancements compared to the original system. The path length of light had been increased by a factor of around 10. The whole apparatus was floated on liquid mercury. Observations were undertaken of relative light fringe positions as the apparatus was rotated though 360 degrees. Key observations were made in the July of 1987 which confirmed the absence of any change of light velocity with direction of light.
This was the key discovery that was to form the basis for the explosion of theory of ‘the new physics’ in years to come. Michelson was inclined to interpret the findings as indicating that the ether was moving with the earth and so no relative motion could be detected. In attempts to rationalise the findings, scientists such as George FitzGerald and Lorenz were advancing theories about how objects contracted their dimensions when in motion – i.e. the FitzGerald-Lorentz contraction’.
Star Gazing and New Beginnings
With the key findings of the Micelson-Morley experiment consigned to history, Michelson’s new research interest became the investigation of the use of light spectra to define a standard of length. Before moving to the newly formed Clark University in Massachusetts, Michelson designed and had built a device called a ‘comparator’ which allowed the expression of a physical length as a finite number of wavelengths of light.
While at Clark University, Michelson was able to make significant scientific progress with designs for interferometers to measure the diameter of astronomical objects. During 1891 he was able to make observations of the moons of Jupiter to determine their diameter using interferometer methods. It was not long, however, that disagreements at Clark University provided a springboard for most of the professors – including Michelson - to be purloined by the University of Chicago in 1892.
Douglas Clarkson - I have always had a keen interest in writing and find that the focus of writing about topics provides the necessary concentration to take ...
Join the Conversation