James Bradley
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James Bradley was an English astronomer and priest who served as the third Astronomer Royal from 1742. He is best known for two fundamental discoveries in astronomy, the aberration of light, and the n
Portrait by Thomas Hudson, c. 1744
Speed of light
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The speed of light is the speed of electromagnetic waves. Light travels at slower speed inside materials like glass or water; its highest speed is in a vacuum. The speed of light in vacuum is a univer
James Bradley
…the Royal Society in January 1729. The theory of the aberration also gave Bradley a means to improve on the accuracy of the previous estimate of the speed of light, which had previously been estimated by the work of Ole Rømer and others. Bradley's published value for the speed of light, expressed as a time of 8…
One of the last and most accurate time of flight measurements, Michelson, Pease and Pearson's 1930–1935 experiment used a rotating mirror and a one-mile (1.6 km) long vacuum chamber which the light beam traversed 10 times. It achieved accuracy of ±11 km/s.
Hendrik Lorentz (right) with Albert Einstein (1921)