Foucault's gyroscope
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ToursExplore Lably’s 3D toursFoucault felt that the results of his famous pendulum experiment had been misunderstood. He therefore endeavored to create an apparatus with a "body freely suspended by its center of gravity and rotating around one of its principal axes", allowing the study of a plane with "absolute directional stability". The mechanical precision of Foucault's gyroscope allowed this to be proven clearly to the scientific establishment, and the gyroscope became a widely popular instrument.
Design
Together with Paul-Gustave Froment, Foucault built an apparatus in which the inner gimbal was balanced on knife edge bearings on the outer gimbal and the outer gimbal was suspended by a fine, torsion-free thread in such a manner that the lower pivot point carried almost no weight.
The gyro was spun to 9,000–12,000 revolutions per minute with an arrangement of gears before being placed into position, which was sufficient time to balance the gyroscope and carry out 10 minutes of experimentation. The instrument could be observed either with a microscope viewing a tenth of a degree scale or by a long pointer.
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Naming
Foucault coined the name "gyroscope" in the 1852 publication of his experiment:
This apparatus specially designed to highlight and approximate the deviation of a freely rotating body can also be used to produce and observe the phenomena of orientation that I have just stated and described. As all these phenomena depend on the movement of the Earth and are its varied manifestations, I propose to name the sole instrument which has served me to observe them gyroscope.
Copies
At least three more copies of a Foucault's gyroscope were made in convenient travelling and demonstration boxes, and copies survive in the UK, France, and the US. The original was given to the Collège de France and was lost, there are no known photographs of the original suggesting it was lost a few decades after the College received it.
The Foucault gyroscope became a challenge and source of inspiration for skilled science hobbyists such as David B. Adamson.