Editing Albert A. Michelson (section)

=== Mount Wilson and Lookout Mountain ===
In 1906, a novel electrical method was used by [[Edward Bennett Rosa|E. B. Rosa]] and the [[National Bureau of Standards]] to obtain a value for the [[speed of light]] of 299,781&nbsp;±&nbsp;10&nbsp;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 (Los Angeles County, California)|Lookout Mountain]], a prominent bump on the south ridge of [[Mount San Antonio]] ("Old Baldy"), some 22 miles distant.

In 1922, the [[United States 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&nbsp;±&nbsp;4&nbsp;km/s.<ref>
{{cite journal
  | url = http://www.pvaa.us/nightwatch/GeodeticMeasurementOfUnusuallyHighAccuracy.pdf
  | last = Garner  | first = C. L.
  | title = A Geodetic Measurement of Unusually High Accuracy
  | journal = Coast and Geodetic Survey Journal
  | date = April 1949
  | pages = 68–74
  | access-date = August 13, 2009
  | archive-url = https://web.archive.org/web/20090325034419/http://www.pvaa.us/nightwatch/GeodeticMeasurementOfUnusuallyHighAccuracy.pdf
  | archive-date = March 25, 2009
  | url-status = dead
}}</ref>

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 intensively detailed 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 [[1925 Santa Barbara earthquake|Santa Barbara earthquake]] of June 29, 1925, which was an estimated magnitude of 6.3 on the [[Richter magnitude scale|Richter scale]].

The now-famous [[Michelson–Morley experiment]] also influenced the affirmation attempts of peer [[Albert Einstein]]'s theory of [[general relativity]] and [[special relativity]], using similar optical instrumentation. These instruments and related collaborations included the participation of fellow physicists [[Dayton Miller]], [[Hendrik Lorentz]], and [[Robert S. Shankland|Robert Shankland]].
[[File:1921 Albert Abraham Michelson.jpg|thumb|[[Autochrome Lumière|Autochrome]] portrait by [[The Archives of the Planet|Auguste Léon]], 1921]]