AWhat changed
Fizeau measures light propagation over a terrestrial round-trip path by observing when a rotating toothed wheel blocks or transmits the returning beam.
Scientific scope
Fizeau measures light propagation over a terrestrial round-trip path by observing when a rotating toothed wheel blocks or transmits the returning beam. The target is the 1849 toothed-wheel experiment in air, not the 1851 moving-water interference experiment or a universal invariant-speed theorem. Light travels to a distant reflector and back through a rotating wheel; eclipse and reappearance depend on its speed and round-trip delay. The paper reports approximately 8633 m separation, 720 teeth, a first eclipse near 12.6 turns per second and a mean from 28 observations in historical units. These are author observations, not a modern exact constant or reconstructed uncertainty budget. Fizeau explicitly promises a fuller memoir after studying the conditions more completely. The speed is a round-trip, path-dependent measurement in air, not a separately synchronized one-way measurement. Formula glyphs and pictures were not certified, and no experiment was replayed. The appended page 132 corrects commission attribution, not the measured speed. Neighboring journal material is outside the target.
Evidence
Source-linked, scoped account of the original work. The published scope states the scientific assumptions and remaining verification limits. WRS has not independently certified the full proof, experimental result or system benchmark.
Contributors
- Hippolyte Fizeau · SCIENCE: Original source-listed scientific author of this scoped work; byline does not determine effort fractions.
- H. Fizeau, Sur une expérience relative à la vitesse de propagation de la lumière (1849), Académie original facsimile
- Académie des sciences Fizeau bibliography:1849 light-speed versus 1851 moving-water work
Provisional WRS assessment, edition 2026-10-16.1. Independent expert calibration is pending. This grade does not certify correctness or assign ownership.
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