Speed of light
History
Until the early modern period, it was not known whether light travelled instantaneously or at a very fast finite speed. The first extant recorded examination of this subject was in ancient Greece.

Speed of light

Section Title: History
Table Section Text: Until the early modern period, it was not known whether light travelled instantaneously or at a very fast finite speed. The first extant recorded examination of this subject was in ancient Greece.

<1638	Galileo, covered lanterns	inconclusive

<1667	Accademia del Cimento, covered lanterns	inconclusive

1675	Rømer and Huygens, moons of Jupiter	220000	‒27% error

1729	James Bradley, aberration of light	301000	+0.40% error

1849	Hippolyte Fizeau, toothed wheel	315000	+5.1% error

1862	Léon Foucault, rotating mirror	298000±500	‒0.60% error

1907	Rosa and Dorsey, EM constants	299710±30	‒280 ppm error

1926	Albert A. Michelson, rotating mirror	299796±4	+12 ppm error

1950	Essen and Gordon-Smith, cavity resonator	299792.5±3.0	+0.14 ppm error

1958	K.D. Froome, radio interferometry	299792.50±0.10	+0.14 ppm error

1972	Evenson et al., laser interferometry	299792.4562±0.0011	‒0.006 ppm error

1983	17th CGPM, definition of the metre	299792.458 (exact)	exact, as defined

Sentence(s)

Hippolyte Fizeau reported the speed of light as 315000.
Hippolyte Fizeau determined the speed of light and reported a value of 315000.
Hippolyte Fizeau determined the speed of light and reported a value of 315000.

final_sentence: Hippolyte Fizeau reported the speed of light as 315000.
final_sentence: Hippolyte Fizeau determined the speed of light and reported a value of 315000.
final_sentence: Hippolyte Fizeau determined the speed of light and reported a value of 315000.