Foucault's gyroscope

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".

[5] Foucault published two papers in 1852, one focused on astronomy with the weight free to move on all three axes (On a new experimental demonstration of the motion of the Earth, based on the fixity of the plane of rotation)[8] and the other on mechanics with the weight free to move on only two axes (On the orientation phenomena of rotating bodies driven by a fixed axis on the Earth's surface.

[9] In the paper on mechanics, Foucault explained that if one axis of rotation is fixed in line with the surface of the Earth, the other two axes of rotation tend to the same direction, similar to "a magnetic needle", making it possible to use the instrument to highlight a directing force.

[10] Foucault coined the name "gyroscope" in the 1852 publication of his experiment:[11][12] 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.At least three more copies of a Foucault's gyroscope were made in convenient travelling and demonstration boxes, and copies survive in the UK,[13] France,[14] and the US.