Before A.A. Michelson took up a prestigious academic offer at Chicago, previous contacts at the International Bureau of Weights and Measures in Paris materialised into a formal invitation to express the standard length of the metre in wavelengths of light.
Defining the Metre
At that time the standard existed as a bar constructed of platinum, iridium and palladium and was kept in a sealed vault. The measurements took longer than expected due to damage to key optical components that had occurred in transit. The process involved dividing the metre length into a number of ‘etalons’ or sections and counting the number of fringes of light equivalent within an etalon. The figure produced using cadmium light was 1553163.5.
On returning to take up his appointment at Chicago, Michelson benefited from the emergent stimulating environment - in particular in astrophysics. Michelson expressed a keen interest in the invention of the spectroheliograph, by George Ellery Hale, for observation of the sun’s corona. Michelson also used the more highly developed laboratory facilities to develop a machine to rule diffraction gratings using diamond cut glass. This exercise was in effect an opportunity to replicate the grating skills of Rowland which Michelson had always admired. The ultra high level of precision involved, however, proved very time consuming, with efforts to perfect the techniques lasting around ten years.
One of the key developments at this time was the construction of the Yerkes telescope with two 42 inch optical lenses. During this period, Michelson was increasingly presented with awards from academic institutions and in 1899 he presented the series of public Lowell Lectures on his investigation of light. Michelson also successfully demonstrated his echelon spectroscope at the Paris Exposition of 1900. Also, Michelson was a key member in founding of the American Physical Society in 1899.
Enter Edna Stanton
It was during this period of increasing recognition, however, that the long strained relationship with his wife Margaret, finally came adrift. Evidence of the final division appeared early in 1897 when Michelson left home and took up residence in a hotel. Divorce proceedings were presented in court in early 1898. The court sided against Michelson on being presented with accounts of Michelson’s apparent cruelty.
Wheels turn, however, in most situations, and friendship with a certain Edna Stanton blossomed into marriage in December of 1899. A new young family emerged, with three girls – Madeline, Beatrice and Dorothy providing plenty of distractions for the eminent Michelson. There were, for example, trips to the his laboratories on Saturday mornings. It was the custom to give the two older children half hour violin lessons each morning before he departed for the laboratory.
Nobel Fame
There is no doubt that the greatest recognition was to come with the award of the Nobel prize for Physics in 1907. Prizes for physics had previously been awarded to Rontgen, Lorentz, Zeeman, Becquerel, the Curies, Rayleigh, Lenard and JJ Thompson. The Nobel committee, however, were unanimous in their verdict in making the award to Michelson out of recognition of the broad range of significant development he had undertaken.
While in the role of visiting professor at the University Gottingen in Germany, Michelson became aware of how divided European scientists were concerning the ‘new’ physics of quantum theory and the ‘old’ physics of light traveling in an ether. It was very much apparent that it had been the experimental genius of Michelson that had prompted Einstein to develop his theories.
With America joining the First World War in April 1917, Michelson remade his Navy links and in June of 1918 reported to Washington to the Bureau of Ordinance. Michelson provided key technical and scientific input into development of a range of optically based systems – including a rangefinder, specialist binoculars for detecting submarines. Also, with no source of high quality German glass available, Michelson provided key information to help America manufacture high quality glass for submarine periscopes.
Final Measurements
Subsequently Michelson spent more time in California at the Mount Wilson Observatory. A previous system to measure the size of stars using iterferometer techniques had been revised and Michelson’s team was able to measure the size of Betelgeuse in Orion. This indicated that this star was in fact 2300 times larger than the sun at a distance of 150 light years. In its day this measurement captured the public imagination.
Additional measurements of the speed of light were undertaken in California on Mount Wilson over a distance of around 35 kilometers. This required the design of new optical structures and use of a very powerful arc lamp. Based on the specific measurement configuration, the condition of correct resonance took place at a specific frequency of revolution of the revolving mirror when the light path returned to the same location as at zero deflection. A value of 299,820 km per second was obtained though it was determined that greater control of the air flow was required to improve accuracy levels.
An additional experiment was carried out in Chicago to determine if the velocity of light is affected by the rotation of the earth. Observations indicated that it was not affected. At this time, Micheleson was recovering from a prostrate operation and it took him several months to recover better health.
Considerations of effects due to turbulence of the air mass in these experiments prompted Michelson to plan an experiment within a mile long evacuated tube – with light being reflected several times from the mirror systems. An experimental installation was set up at the Irvine Ranch near Pasadena with extensive establishment funding.
Due to recurrent illness, Michelson was not able to spend as much time as he would have liked to solve some nagging technical issues relating to the findings, where fluctuations of up to 12 miles per second were being observed. His last visit to the site was in March 1931. This also co-incided with a visit of Einstein to his hotel.
Spurred on by news of Michelson’s failing health, the investigators at the Irvine Ranch worked flat out to establish definitive measurements which they announced to him as 299,774 km/sec on the 7th of May. Michelson started to dictate the text of a report of the experiment but the effort exhausted him and he fell into a deep peaceful sleep. He died on the morning of the 9th of May, 1931. In fact the measurements made at Mount Wilson were closer to the accepted value of the speed of light.
Epitaph
Some of the essential perspective on A.A. Michelson has been provided by his daughter Dorothy who was about 30 when he died.
There can be no doubt that Michelson made his best endeavors in the call of science and especially in development of scientific instrumentation and the science of associated measurement. He was able to develop superb instrumentation systems and provide huge support and knowledge in the expansion the scientific might of America.
Through the studies of his scientific work and the accounts of peers and colleagues which are documented, a picture emerges of an admirable individual fascinated by the lure of science and her secrets and in which the mystery of the nature and properties of light held absolute fascination.
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 ...
