A treatise on gyrostatics and rotational motion . ntalist, Leon Foucault,* suggested twoways bf determining the rotation ofthe earth. One was observation of theapparent turning of the plane of vibration(if a long pendulum, suspended so as to beas nearly as possible free from any con-straint due to the attachment of the pen-dulum wire to its fixed support; Thisclassical experiment was carried out withfair success at the Pantheon at Paris, andwas repeated under the domes of thecathedrals of Amiens and Rheims. Foucaults other method was based onthe fact that a gyrostat, if mountedproperly, retain
A treatise on gyrostatics and rotational motion . ntalist, Leon Foucault,* suggested twoways bf determining the rotation ofthe earth. One was observation of theapparent turning of the plane of vibration(if a long pendulum, suspended so as to beas nearly as possible free from any con-straint due to the attachment of the pen-dulum wire to its fixed support; Thisclassical experiment was carried out withfair success at the Pantheon at Paris, andwas repeated under the domes of thecathedrals of Amiens and Rheims. Foucaults other method was based onthe fact that a gyrostat, if mountedproperly, retains unaltered the directionof the spin-axis when the supports areturned round. Take. For example, thepedestal gyrostat of Fig. 32. The flywheelis within the frame there shown as carriedby a vertical rod, which swivels in avertical socket projecting upward fromthe supporting stand. Rods with arrow-points are attached, to be set torepresent the spin axis, the couple axis, and the direction of rotation. If * (oni/i/i -• rendua, •>.> (1852),. Fio. 32. vii PHYSICAL APPLICATIONS OF GYROSTATS 133 tin spinning gyrostat has its siiin axis in any chosen direction, and tin-supporting stand is turned round, a Eriction couple of some little magni-tude is applied to the vertical rod; nevertheless, the direction of thespin-axis is mit altered perceptibly. Yet the Eriction couple is sufficientto carry the gyrostal round with the stand when there is no spin. TheBpin results in a great increase of virtual inertia Eor turning displacements,as we shall see quantitatively in one of the arrangements described belowin the present chapter. It is to he understood that when there is no weight hung on the gyrostatcase, the axes XX. YY, ZZ intersect at the common centre of gravity ofthe flywheel and case, and that there is no friction couple about any ofthese axes. When the axis of spin of the pedestal gyrostat is adjusted to be accuratelyhorizontal, and to point north, the horizontal component of
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