Sperry Gyro Compass.Electrically-driven gyroscope, revolving at about 9000 revolutions per minute, that carries corrector devices for precessing it into the meridian and maintaining it there. A 'phantom' follows all movements of axle relative to vessel's fore and aft line. Sphere. Solid figure generated by half revolution of a circle about one of its diameters. Spherical Aberration. Deviation of light rays from a focus after passing through curved lens. Results in a coloured fringe caused by unequal refraction of lenses breaking up the light into its constituent colours.