Definition:Speed of Light/Historical Note
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Historical Note on Speed of Light
Until the $1983$ definition of the metre as exactly $\dfrac 1 {299 \, 792 \, 458}$ of the distance travelled by light in $1$ second, the speed of light has been the subject of measurement.
This measurement has been accomplished to greater and greater accuracy over the course of history.
| Date | Technique | Value $(\mathrm {km} \, \mathrm s^{-1})$ | Tolerance | Error | |
|---|---|---|---|---|---|
| $1675$ | Ole Christensen Rømer and Christiaan Huygens | observing the moons of Jupiter | $220 \, 000$ | $-27 \%$ | |
| $1729$ | James Bradley | aberration of light | $301 \, 000$ | $+0 \cdotp 40 \%$ | |
| $1849$ | Armand Hippolyte Louis Fizeau | toothed wheel | $315 \, 000$ | $+5 \cdotp 1 \%$ | |
| $1862$ | Jean Bernard Léon Foucault | rotating mirror | $298 \, 000$ | $\pm 500$ | $−0 \cdotp 60 \%$ |
| $1907$ | Rosa and Dorsey | EM constants | $299 \, 710$ | $\pm 30$ | $−280$ ppm |
| $1926$ | Albert Abraham Michelson | rotating mirror | $299 \, 796$ | $\pm 4$ | $+12$ ppm |
| $1950$ | Essen and Gordon-Smith | cavity resonator | $299 \, 792 \cdotp 5$ | $\pm 3 \cdotp 0$ | $+0 \cdotp 14$ ppm |
| $1958$ | K.D. Froome | radio interferometry | $299 \, 792 \cdotp 50$ | $\pm 0 \cdotp 10$ | $+0 \cdotp 14$ ppm |
| $1972$ | Evenson et al. | laser interferometry | $299 \, 792 \cdotp 4562$ | $\pm 0 \cdotp 0011$ | $−0 \cdotp 006$ ppm |