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In: Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences 32, Paris, Bachelier, 1851. 4to. (266 x 216 mm); pp. 135-138 (entire volume: 1010 pages). New endpapers. Library stamp and deaccession stamp of Universitätsbibliothek Paderborn and some additional library markings on the lower margin of page 2. Pages 959 to 1010 (index according to author and topic) in facsimile. Modern cloth with gilt-embossed spine. Internally crisp and bright throughout. ---- PMM 330, Dibner 17, Norman 818 (offprint). - THE FIRST MECHANICAL DEMONSTRATION OF THE EARTH'S ROTATION FIRST EDITION, RARE. To postulate astronomical behaviour is one order of thought, to prove its demonstration is of quite another order. The rotation of the earth had been accepted since Copernicus but it remained for Foucault to demonstrate it. He suspended an iron ball pendulum from the dome of the Pantheon in Paris, set it swinging and chartered its constantly rotating angular shift and proved it to rotate completely in one day." (Dibner, Heralds of Science 17). Although the rotation of the earth had been accepted since Copernicus, it was Foucault who first demonstrated it by experiment."His early experiments were private, but Louis Napoleon (later Napoleon III) became so interested that he arranged for them to be repeated publicly. This was a splendid affair which took place in the Pantheon in 1851 before a fashionable audience. A heavy ball was suspended from the dome on a wire 220 feet long; beneath the ball was a table 12 feet in diameter covered with sand on which the ball would leave a mark. This is known as 'Foucault's pendulum'. It soon became apparent that the plane in which the pendulum was swinging moved in a clockwise direction and in about thirty-two hours the plane of vibration had completed a full circuit. The audience in the Pantheon was greatly impressed; some ladies fainted with excitement, while other spectators maintained that they could feel the earth move beneath them" (PMM 330). "Continuing to experiment on the mechanics of the earth's rotation, Foucault in 1852 invented the gyroscope, which, he showed, gave a clearer demonstration than the pendulum of the earth's rotation and had the property, similar to that of the magnetic needle, of maintaining a fixed diretion. Foucault's pendulum and gyroscope had more than a popular significance (which continues to this day). First, they stimulated the development of theoretical mechanics, making relative motion and the theories of the pendulum and the gyroscope standard topics for study and investigation. Second, prior to Foucault's demonstrations, the study of those motions on the earth's surface in which the deflecting force of rotation plays a prominent part (especially winds and ocean currents) was dominated by unphysical notions of how this force acted. Foucault's demonstrations and the theoretical treatments they inspired showed conclusively that this deflecting fore acts in all horizontal directions, thus providing the sound physical insight on which Buys Ballot, Ferrel, Ulrich Vettin, and others could build" (Dictionary of Scientific Biography V, p. 86). N° de ref. del artículo 001723
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