Item History: Working on a simple experimental proof for the rotational motion of the earth, the French physicist Léon Foucault introduced in 1852 the term Gyroscope for an instrument being able to observe such movements. Besides his well-known pendulum, these investigations concentrated on gyros with cardanic suspension. Foucault recognized especially that a well-directed restraint of the motion of the gimbals (like blocking one degree of freedom of the suspension) leads to specific indicators detecting different rotation components. With that, he paved the way for such important navigation instruments like the artificial horizon, the gyrocompass, the directional gyro, and inertial navigation systems. Nevertheless, L. Foucault is not the originator of that mechanical principle. He was familiar with it because such gyros were especially popular in France during the 19th century: they were already employed in numerous French schools to explain the precession of the earth rotation axis. This matter was born of the initiative of the French mathematician Pierre-Simon Laplace, who recommended introducing that kind of gyros as teaching aid. It is likely that P.-S. Laplace referred initially to a specimen that was in possession of the École Polytechnique in Paris. This apparatus is mentioned in 1813 by one of his former students, the French mathematician S. Denis Poisson: In a paper on analysing the dynamics of rotating bodies (Poisson 1813), he uses the gyro with cardanic suspension as an example, and he names the inventor of the mechanism. It was his contemporary German colleague J.G. Friedrich Bohnenberger being Professor for mathematics, astronomy, and physics at the University of Tübingen, Germany. This scientist explained for the first time the design and the use of such an apparatus (Bohnenberger 1817). As Bohnenberger could inevitably not yet know the term gyroscope, he called the device simply Machine. Therefore, the Machine of Bohnenberger (often less correctly named the Apparatus or Gyroscope of Bohnenberger) was the basis for Foucault’s epochal work on gyros.
In his original publication of 1817, Bohnenberger indicates at the beginning that several copies of the first Machine had been manufactured in Tübingen, and at the end of the article he names the manufacturer and the price of the Machine: All devices were assembled by the “Universitätsmechanicus” Johann W.G. Buzengeiger and could be bought for 18 Gulden (roughly one monthly salary for Bohnenberger). Despite this hint, all of the initial specimens of Bohnenberger’s Machine seemed to be lost since a long time. Fortunately, in December 2004 one of them was rediscovered during a stocktaking at the Kepler-Gymnasium (high school) in Tübingen.
For additional information see: Wagner, J.; Sorg, H.; Renz, A.: The Machine of Bohnenberger. European Journal of Navigation 3 (2005), No. 4, pp. 69-77