A rotating wheel, mounted in a ring or rings, for illustrating the dynamics of rotating bodies, the composition of rotations, etc. It was devised by Professor W. R. Johnson, in 1832, by whom it was called the rotascope.
A form of the above apparatus, invented by M. Foucault, mounted so delicately as to render visible the rotation of the earth, through the tendency of the rotating wheel to preserve a constant plane of rotation, independently of the earth's motion.
A spinning wheel on a mount that allows the axle to swing freely. If a constant twist is applied to the axle, for instance by supporting the weight from one end only, the axle will swing uniformly along the axis of the twist in a motion called precession.