Albert Abraham Michelson

Albert Abraham Michelson, (pronunciation anglicized as "Michael-son", December 19, 1852 - May 9, 1931), was a Prussian-born American physicist known for his work on the measurement of the speed of light, and especially for the Michelson-Morley experiment. In 1907 he received a Nobel prize for physics, the first American to receive the Nobel Prize in the sciences.

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.

Related Topics:
1877 - US Navy - Léon Foucault - Optics - 1878 - Simon Newcomb - Nautical Almanac Office - 1879 - Washington DC

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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.

Related Topics:
Newcomb - 1883

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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.

Related Topics:
1906 - E. B. Rosa - N. E. Dorsey - National Bureau of Standards - Speed of light

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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.

Related Topics:
1920 - Mount Wilson Observatory - Mount San Antonio

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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.

Related Topics:
1922 - U.S. Coast and Geodetic Survey - Invar - 1924

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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).

Related Topics:
Santa Barbara - Earthquake - 29 June - 1925 - Richter scale

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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.

Related Topics:
1927 - Speed of light - Electro-optic - 1926

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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.

Related Topics:
1930 - Francis G. Pease - Fred Pearson - Km - Pasadena, California - Electro-optic - 1935

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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.

Related Topics:
1887 - Edward Williams Morley - Michelson-Morley experiment - Earth - Aether - Light - Null result - Albert Einstein - Theory of Relativity

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