gyroscope

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A device consisting of a spinning mass, typically a disk or wheel, mounted on a base so that its axis can turn freely in one or more directions and thereby maintain its orientation regardless of any movement of the base.

Century Dictionary and Cyclopedia

1. n. An instrument consisting of a fly-wheel, the axis of which can turn freely in any direction, designed to illustrate the dynamics of rotating bodies. The instrument commonly called gyroscope is better named gyroscopic top (which see, under gyroscopic). The gyroscope proper of Foucault, shown in the figure, consists of a flywheel having the small conical bearings of its axis in a well-balanced metallic ring which carries two knife-edges in a line perpendicular to the axis of the fly-wheel; these knife-edges bear upon agates carried in a horizontal plane by an outer vertical ring half suspended from a small copper wire and turning about a vertical axis. The axis of the wheel can thus turn in any direction. By means of an accessory apparatus a velocity of 150 turns a second can be imparted to the fly-wheel. The principal experiments with this apparatus are as follows: First experiment.— If, when the fly-wheel is turning rapidly, no considerable force is applied to change the direction of its axis, its direction will remain almost unchanged. For, suppose it were proposed, by an instantaneous impulse, to turn this axis round a fixed axis perpendicular to it; then, at the point where this fixed axis cuts the rim of the fly-wheel, a particle would have to be deflected, and it can be shown by the parallelogram of motions that a velocity must be communicated to it proportional to the velocity it already possessed. Hence, the force required to rotate the axis of a fly-wheel increases with its velocity. Accordingly, when the velocity is very high, the friction on the bearings will change the direction of the axis but very little. But all the surrounding objects partake of the rotation of the earth upon its axis. Consequently, the axis of the fly-wheel will have a relative rotation; and this may be observed with a microscope. Second experiment.— If the fly-wheel was attached to its axis by a hinge, so that its plane was free to take any inclination to the axis, it is plain that by virtue of centrifugal force it would become perpendicular to the axis, since in this way its particles would be furthest from the axis. If then the outer ring of the gyroscope be held fast in such a position that the axis of the fly-wheel is free to move in the meridian plane, it partakes of the rotation of the earth; and the rotation of the earth and that of the fly-wheel being compounded, the axis of resultant rotation is not quite perpendicular to the fly-wheel. Accordingly, the inner ring will turn on its knife-edges until the axis of the fly-wheel is brought into parallelism with that of the earth, so that the wheel revolves from west to east like the earth. Third experiment.—On the same principle, if the outer ring be free to turn, but the inner one be fixed horizontally, the outer ring will turn so as to bring the axis of the fly-wheel into the meridian. Fourth experiment.—Let the inner wheel be thrown out of balance by hanging a weight upon it near one end of the axis; then this weight will each instant communicate a rotation about the knife-edges, compounding itself with the rotation of the fly-wheel about its axis as the rotation of the earth does in the third experiment, and a rotation of the outer ring round its vertical axis will result. Since the resultant axis of the first two rotations is very near that of the fly-wheel, the tendency of the weight to fall will be but slight, and under the influence of the centrifugal force of the third rotation it will move like a conical pendulum.

Wiktionary

1. n. an apparatus composed of a wheel which spins inside of a frame (gimbal) and causes the balancing of the frame in any direction or position. In the form of gyroscopic stabilizer, used to help keep aircraft and ships steady.

GNU Webster's 1913

1. n. 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. n. A form of 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.

WordNet 3.0

1. n. rotating mechanism in the form of universally mounted spinning wheel that offers resistance to turns in any direction