Gy'ro-scōpe, n.

n. [Gr. γῦρος, ring, circle, and σκοπεῖν, to view.]

1. A piece of apparatus, consisting of a rotating wheel mounted in a ring or rings, in different ways, for illustrating the dynamics of rotating bodies, the composition of rotations, &c. It is a modification of Bohnenberger’s machine, and was first 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.