Gy"ro*scope (jī"r&osl;*skōp), n. [Gr. gy^ros ring, circle + - scope.] 1. 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.

2. 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.

• an apparatus composed of a wheel which spins inside of a frame and causes the balancing of the frame in any direction or position. Often used in helping to keep aircraft and ships steady.