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Encyclopedia > Albert A. Michelson
Albert Abraham Michelson.

Albert Abraham Michelson, (December 19, 1852 _ May 9, 1931), was a Polish-American physicist known for his work on the measurement of the speed of light. In 1907 he received a Nobel prize for physics.

Contents

Life

Michelson was born in Strzelno, Poland (then Strelno, Provinz Posen Kingdom of Prussia). He moved to the United States with his parents when he was two years old.


In 1869, Michelson entered the US Naval Academy at Annapolis, Maryland and graduated in 1873. Early on, Michelson was fascinated with the sciences and the problem of measuring the speed of light in particular. After two years of studies in Europe he resigned from the navy in 1881. In 1883 he accepted a position as professor of physics at the Case School of Applied Science in Cleveland, Ohio and concentrated on developing an improved interferometer.


After serving as professor at Clark University at Worcester, Massachusetts from 1889, in 1892 Michelson was appointed professor and the first head of the department of physics at the newly organized University of Chicago. In 1907, Michelson became the first American to receive a Nobel Prize in Physics. He also won the Copley Medal in 1907, the Henry Draper Medal in 1916, the Gold Medal of the Royal Astronomical Society in 1923. A crater on the Moon is named after him.


Michelson died on May 9, 1931 in Pasadena, California.


Speed of light

Early measurements

As early as 1877, while still an officer in the US Navy, Michelson started planning a refinement of the rotating_mirror method of Léon Foucault for measuring the speed of light, using improved optics and a longer baseline. He conducted some preliminary measurements using largely improvised equipment in 1878 about which time his work came to the attention of Simon Newcomb, director of the Nautical Almanac Office who was already advanced in planning his own study. Michelson published his result of 299,910±50 km/s in 1879 before joining Newcomb in Washington DC to assist with his measurements there. Thus began a long professional collaboration and friendship between the two.


Newcomb, with his more adequately funded project, obtained a value of 299,860±30 km/s, just at the extreme edge of consistency with Michelson's. Michelson continued to "refine" his method and in 1883 published a measurement of 299,853±60 km/s, rather closer to that of his mentor.


Mt Wilson and Lookout Mtn 1926

In 1906, a novel electrical method was used by E. B. Rosa and N. E. Dorsey of the National Bureau of Standards to obtain a value for the speed of light of 299,781±10 km/s. Though this result has subsequently been shown to be severely biased by the poor electrical standards in use at the time, it seems to have set a fashion for rather lower measured values.


From 1920, Michelson started planning a definitive measurement from the Mount Wilson Observatory, using a baseline to Lookout Mountain, a prominent bump on the south ridge of Mount San Antonio (Old Baldy), some 22 miles distant.


In 1922, the U.S. Coast and Geodetic Survey began two years of painstaking measurement of the baseline using the recently available invar tapes. With the baseline length established in 1924, measurements were carried out over the next two years to obtain the published value of 299,796±4 km/s.


Famous as the measurement is, it was beset by problems, not least of which was the haze created by the smoke from forest fires which blurred the mirror image. It is also probable that the heroic work of the Geodetic Survey, with an estimated error of less than one part in 1 million, was compromised by a shift in the baseline arising from the Santa Barbara earthquake of 29 June 1925 (estimated magnitude 6.3 on the Richter scale).


Michelson, Pease & Pearson 1932

The period after 1927 marked the advent of new measurements of the speed of light using novel electro_optic devices, all substantially lower than Michelson's 1926 value.


Michelson sought another measurement but this time in an evacuated tube to avoid difficulties in interpreting the image owing to atmospheric effects. In 1930, he began a collaboration with Francis G. Pease and Fred Pearson to perform a measurement in a 1.6 km tube at Pasadena, California. Michelson died with only 36 of the 233 measurement series completed and the experiment was subsequently beset by geological instability and condensation problems before the result of 299,774±11 km/s, consistent with the prevailing electro-optic values, was published posthumously in 1935.


Interferometry

In 1887 he collaborated with colleague Edward Williams Morley in the Michelson_Morley experiment. Their experiment for the expected motion of the Earth relative to the aether, the hypothetical medium in which light was supposed to travel, resulted in a null result. It is quite certain that Albert Einstein knew of the work (according to his 1905 paper), and it greatly assisted the acceptance of the Theory of Relativity.


Electronic books

These works of Albert Abraham Michelson are freely available in electronic form from Project Gutenberg:

  • Experimental Determination of the Velocity of Light (http://www.gutenberg.net/browse/BIBREC/BR11753.HTM)

References

  • Livingston, D. M. (1973). The Master of Light: A Biography of Albert A. Michelson ISBN 0226487113 _ biography by Michelson's daughter

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