300,000,000

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In the 19th century Hippolyte Fizeau developed a method to determine the speed of light based on time-of-flight measurements on Earth and reported a value of 315 000km/s. [143] His method was improved upon by Léon Foucault who obtained a value of 298 000km/s in 1862. [104] In the year 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch measured the ratio of the electromagnetic and electrostatic units of charge, 1/ √ ε 0 μ 0, by discharging a Leyden jar, and found that its numerical value was very close to the speed of light as measured directly by Fizeau. The following year Gustav Kirchhoff calculated that an electric signal in a resistanceless wire travels along the wire at this speed. [144]

Bartlett, D. J.; Desmond, H.; Ferreira, P. G.; Jasche, J. (17 November 2021). "Constraints on quantum gravity and the photon mass from gamma ray bursts". Physical Review D. 104 (10): 103516. arXiv: 2109.07850. Bibcode: 2021PhRvD.104j3516B. doi: 10.1103/PhysRevD.104.103516. ISSN 2470-0010. S2CID 237532210.a b c Boyer, CB (1941). "Early Estimates of the Velocity of Light". Isis. 33 (1): 24. doi: 10.1086/358523. S2CID 145400212. HKUST Professors Prove Single Photons Do Not Exceed the Speed of Light". The Hong Kong University of Science and Technology. 19 July 2011. In classical physics, light is described as a type of electromagnetic wave. The classical behaviour of the electromagnetic field is described by Maxwell's equations, which predict that the speed c with which electromagnetic waves (such as light) propagate in vacuum is related to the distributed capacitance and inductance of vacuum, otherwise respectively known as the electric constant ε 0 and the magnetic constant μ 0, by the equation [58] c = 1 ε 0 μ 0 . {\displaystyle c={\frac {1}{\sqrt {\varepsilon _{0}\mu _{0}}}}\ .}

Amelino-Camelia, G (2009). "Astrophysics: Burst of support for relativity". Nature. 462 (7271): 291–292. Bibcode: 2009Natur.462..291A. doi: 10.1038/462291a. PMID 19924200. S2CID 205051022.Hernández-Figueroa, HE; Zamboni-Rached, M; Recami, E (2007). Localized Waves. Wiley Interscience. p.26. ISBN 978-0-470-10885-7. a b c Zhang, YZ (1997). Special Relativity and Its Experimental Foundations. Advanced Series on Theoretical Physical Science. Vol.4. World Scientific. pp. 172–173. ISBN 978-981-02-2749-4 . Retrieved 23 July 2009.