The gyroscope or rotascope, an instrument illustrating the tendency of rotating bodies to preserve their plane of rotation. The spindle of the metallic disk, C, is fitted to turn easily in bearings in the ring, A. If the disk is set in rapid rotary motion on its axis, and the pintle, F, at one side of the ring, A, is placed on the bearing in the top of the pillar, G, the disk and ring seem indifferent to gravity, and instead of dropping begin to revolve about the vertical axis.