1,078,356. Gyroscopic apparatus. LITTON INDUSTRIES Inc. Oct. 22, 1964 [Nov. 15, 1963], No.43222/64. Heading G1C. Gyroscopic apparatus comprises a shaft 23 driven by a motor 27, and a ring shaped rotor 21 secured for rotation with the shaft 23 by two diametrically opposed torsion bars 24 with its plane at right angles to the axis of the shaft, the arrangement being such that if the axis of the shaft is angularly displaced the rotor 21 will oscillate about the axes of the bars 24, the rate of rotation of the shaft 23 being equal to the frequency of oscillation of rotor 21 so that the amplitude of the oscillations will be proportional to the angular displacement of the shaft. The rotor is enclosed within an evacuated housing 32 to reduce damping of the rotor oscillations.; The torsion bars 24 are of cruciform cross-section in order to provide maximum bending resistance while presenting a small elastic strength about their axes to minimise hysteresis losses. The rotor 21 is mounted on the bars 24 by two diaphragms 25 which ensure that the flexure characteristics of the ring mounting are uniform in all directions thus reducing errors caused by shift of the centre of gravity of the ring on sudden accelerations. A pick-off (35) and torquer (36) Fig. 5 (not shown) for the rotor are provided and these each comprise a coil (43) carried by the rotor in a recess therein, and cooperating polepieces (39, 41) mounted on the interior of the housing (32). The oscillations of the ring are sensed by the pick-off (35) and are fed to a winding 45 Fig. 3 on the exterior of the casing 32 and thus to a rotary pick-off transformer 47.; The torquer 36 which may be employed to nullify the rotor vibrations, or to provide torques for changing its attitude is fed from a D. C. source through a pair of fixed primary windings 49, 50 arranged in quadrative and through a coil 51 carried by the shaft 23. There is also provided an output timing device for establishing a reference phase and this comprises a permanent magnet 53 rotating with the shaft 23 and a pick-up coil 54. In an alternative form, Fig. 6, a casing 66 carrying pole pieces 67 for the driving motor 64 also supports a ring-shaped rotor 70 by way of torsion bars 68. The rotor is enclosed inside an evacuated casing 60 and its vibrations are sensed by an E-type pickoff 71. A temperature sensing device 72 is also provided and this may control a temperature control device.; The gyroscopic devices described above may be utilized in the stabilized element of an inertial guidance system Fig. 7 (not shown) wherein two of the above described devices are arranged with their sensitive axes disposed so that their outputs may be resolved to give attitude data with respect to the co-ordinate reference axes of the system, accelerometers being provided to sense accelerations, along each of the three co-ordinate axes, and the stabilized element carrying these devices being mounted in a three ring system provided with the torquers and pick-offs necessary for the stabilization of the element and the production of navigational data. Details of the electrical arrangements are given in the Specification.