Episode 1 of 1
Terrestrial Measurement of Light Speed
- When
- 1849
- Where
- Earth-based experimental setup
Fizeau measured the speed of light on Earth using a toothed wheel, reporting 315,000 km/s and surpassing Rømer's 1676 estimate in precision.
In 1849, Fizeau used a toothed-wheel apparatus for time-of-flight measurement on Earth. The wheel's speed was increased until, at 12.6 rotations per second, the returning light hit the next tooth and disappeared; at 25.2 rotations per second the computed value was 313,274,304 m/s, within 5% of the correct value of 299,792,458 m/s. He reported 315,000 km/s, a better precision than Rømer's 1676 value.
Sources
- Hippolyte Fizeau Wikipedia, revision of 2026-10-03
- Speed of light Wikipedia, revision of 2026-09-27
Machine-drafted from the cited Wikipedia passages and checked by a reviewing model, not by a human editor. Every passage cites the revision it was written from; dates and places follow those passages.