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    "id": "foucault-pendulum-earth-rotation-1851",
    "title": "Foucault: making Earth rotation visible with a pendulum",
    "summary": "Foucault observes a gradual change in the direction of a carefully released pendulum swing and interprets its local precession as an observable consequence of Earth rotation.\n\nA long pendulum supplies a direction that changes relative to the floor as Earth turns. Foucault minimizes unwanted twist and sideways release, then follows the swing against a fixed marker. The effect accumulates, making a planetary motion visible within a room. Its rate depends on latitude: the polar picture cannot simply be applied everywhere. The short 1851 note connects observed direction and approximate size to that dependence, while acknowledging earlier mechanics and the help needed to build the apparatus.",
    "boundary": "The target is Foucault's February 1851 pendulum note, read in its contemporary English translation and French transcription. An initially planar swing requires controlled release, a suitable homogeneous round suspension wire and minimized torsion. The ideal polar argument is distinct from the approximate local-latitude law: angular precession is Earth's angular motion multiplied by the sine of latitude, with secondary effects neglected. It vanishes at the equator and reverses in the other hemisphere; it is not a full 24-hour revolution at every site or a fixed three-dimensional plane everywhere. The brief note announces the law without a full derivation. It reports a 2 m cellar apparatus and an 11 m observatory apparatus, with qualitative and approximate amount comparisons. The later Panthéon installation appears only in an editorial addition. No calibrated uncertainty, apparatus replay, orbital-motion test or independent transcription certification is claimed. Poisson's prior theory and later optical rotation tests retain distinct credit.",
    "area": "Mechanics and physical Earth rotation",
    "topic": "Physics",
    "year": 1851,
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        "description": "The target is Foucault's February 1851 pendulum note, read in its contemporary English translation and French transcription. An initially planar swing requires controlled release, a suitable homogeneous round suspension wire and minimized torsion. The ideal polar argument is distinct from the approximate local-latitude law: angular precession is Earth's angular motion multiplied by the sine of latitude, with secondary effects neglected. It vanishes at the equator and reverses in the other hemisphere; it is not a full 24-hour revolution at every site or a fixed three-dimensional plane everywhere. The brief note announces the law without a full derivation. It reports a 2 m cellar apparatus and an 11 m observatory apparatus, with qualitative and approximate amount comparisons. The later Panthéon installation appears only in an editorial addition. No calibrated uncertainty, apparatus replay, orbital-motion test or independent transcription certification is claimed. Poisson's prior theory and later optical rotation tests retain distinct credit.",
        "domain": "Mechanics and physical Earth rotation"
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      "sources": [
        {
          "citation": "M. L. Foucault, Physical Demonstration of the Rotation of the Earth by Means of the Pendulum (1851), contemporary Franklin Institute translation",
          "url": "https://zenodo.org/records/2429355/files/article.pdf?download=1"
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        {
          "citation": "Léon Foucault, Démonstration physique du mouvement de rotation de la Terre au moyen du pendule (1851), French original text transcription",
          "url": "https://fr.wikisource.org/w/index.php?title=D%C3%A9monstration_physique_du_mouvement_de_rotation_de_la_Terre_au_moyen_du_pendule&oldid=4224751"
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      "statement": "# Foucault: making Earth rotation visible with a pendulum\n\nFoucault observes a gradual change in the direction of a carefully released pendulum swing and interprets its local precession as an observable consequence of Earth rotation.\n\nA long pendulum supplies a direction that changes relative to the floor as Earth turns. Foucault minimizes unwanted twist and sideways release, then follows the swing against a fixed marker. The effect accumulates, making a planetary motion visible within a room. Its rate depends on latitude: the polar picture cannot simply be applied everywhere. The short 1851 note connects observed direction and approximate size to that dependence, while acknowledging earlier mechanics and the help needed to build the apparatus.\n\n## Scientific scope\n\nThe target is Foucault's February 1851 pendulum note, read in its contemporary English translation and French transcription. An initially planar swing requires controlled release, a suitable homogeneous round suspension wire and minimized torsion. The ideal polar argument is distinct from the approximate local-latitude law: angular precession is Earth's angular motion multiplied by the sine of latitude, with secondary effects neglected. It vanishes at the equator and reverses in the other hemisphere; it is not a full 24-hour revolution at every site or a fixed three-dimensional plane everywhere. The brief note announces the law without a full derivation. It reports a 2 m cellar apparatus and an 11 m observatory apparatus, with qualitative and approximate amount comparisons. The later Panthéon installation appears only in an editorial addition. No calibrated uncertainty, apparatus replay, orbital-motion test or independent transcription certification is claimed. Poisson's prior theory and later optical rotation tests retain distinct credit.\n\n## People and systems\n\nLéon Foucault\n\n\n\n## Original sources\n\n- [M. L. Foucault, Physical Demonstration of the Rotation of the Earth by Means of the Pendulum (1851), contemporary Franklin Institute translation](https://zenodo.org/records/2429355/files/article.pdf?download=1)\n- [Léon Foucault, Démonstration physique du mouvement de rotation de la Terre au moyen du pendule (1851), French original text transcription](https://fr.wikisource.org/w/index.php?title=D%C3%A9monstration_physique_du_mouvement_de_rotation_de_la_Terre_au_moyen_du_pendule&oldid=4224751)\n",
      "summary": "Foucault observes a gradual change in the direction of a carefully released pendulum swing and interprets its local precession as an observable consequence of Earth rotation.\n\nA long pendulum supplies a direction that changes relative to the floor as Earth turns. Foucault minimizes unwanted twist and sideways release, then follows the swing against a fixed marker. The effect accumulates, making a planetary motion visible within a room. Its rate depends on latitude: the polar picture cannot simply be applied everywhere. The short 1851 note connects observed direction and approximate size to that dependence, while acknowledging earlier mechanics and the help needed to build the apparatus.",
      "title": "Foucault: making Earth rotation visible with a pendulum"
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    "what_changed": "Foucault observes a gradual change in the direction of a carefully released pendulum swing and interprets its local precession as an observable consequence of Earth rotation.",
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    "evidence_summary": "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.",
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      {
        "title": "M. L. Foucault, Physical Demonstration of the Rotation of the Earth by Means of the Pendulum (1851), contemporary Franklin Institute translation",
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        "title": "Léon Foucault, Démonstration physique du mouvement de rotation de la Terre au moyen du pendule (1851), French original text transcription",
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