245,546. Henderson, Sir J. B. Oct. 29, 1924. Gyroscopic apparatus. - A gyro-compass or other gyroscopic instrument for use on a moving body and having gravitational control is provided with means for reproducing in the instrument, when the body is stationary, the effects which would be produced by a change of speed or course of the body. The invention is more particularly intended for use with a compass &c. in which the effects of such changes are compensated, in order that the accuracy of such compensation may be tested when the instrument is at rest. The manner in which the acceleration is imitated depends on the nature of the compensation applied to the compass; for example, the compensation may be such as to cause the compass to deviate in azimuth to the virtual meridian, or in some cases it may be such as to prevent any ballistic deflection in azimuth, so that the compass remains on the real meridian. The Figure shows a compensated periodic compass similar in principle to that described in Specification 188,390, the compass, apart from the compensating-means, being of the type shown in Fig. 14 of Specification 166,570. The rotor casing 1 is mounted in neutral equilibrium on pivots 2 in a ring 3 which is supported on pivots 4 in a ring 5 forming part of the follow-up frame 6 from which the ring 3 is suspended by the filar 7. The gear ring 30 on the follow-up frame is supported by ball bearings 31 on a ring 32 attached by arms 33 to the binnacle gimbal-ring 34. Gravity control is obtained by a level comprising two mercury containers 11 connected bv tubes 12 held in brackets 13 which are supported on trunnions 14a, 14b on the horizontal diameter of the ring 5. The level is connected by an arm 15 and fork 16 to a pin 17 on the casing 1, this pin being in known manner displaced from the vertical axis of the casing. The level control can be regulated so that the torque about the horizontal produced by the displacement of mercury when acceleration occurs just moves the axis of the gyroscope into the virtual meridian : at the same time the torque about the vertical causes a tilt in the virtual meridian plane. To imitate the effects of an acceleration the level is adapted to be tilted manually relativev to the casing 1, the trunnion 14<a> being carried by an arm 18 mounted on a pivot 19 on the ring 5. The arm 18 is provided with a toothed segment 22 gearing with a pinion 20 which is operated by a graduated knob 23 for which an index 24 is provided. To imitate the rate of change of the horizontal plane which would be produced by the rate of change of latitude due to the acceleration, a torque about the vertical is applied by twisting the filar 7 by means of bevel gear 26, 27 operated manually by a knob 25. In using the testing means, the knob 23 is quickly turned through the desired angle and left so turned for a stated time. During this time the knob 25 is turned through a number of equal steps, say 20, at intervals of three seconds, the total rotation of the knob 25 corresponding to that of the knob 23. At the end of this time the knob 23 is turned back to its zero position. As an alternative to the twisting of the suspension, a weight may be attached to a hook 28 on the casing 1 on the side opposite to that towards which the level is displaced, the weight being just sufficient to counterbalance the torque about the horizontal produced by the displacement of the level. In this case the gyro-axis remains in the real meridian but becomes tilted by the torque about the vertical. The testing means may be applied to a compass such as that described in Specification 188,390, which is compensated so as to be free from ballistic deviation and also from tilt resulting from the acceleration, so that the axis remains horizontal on the real meridian. The Figure shows means for applying the compensation, which takes the form of (a) preventing disturbances during the acceleration and (2) preventing disturbances subsequent to the acceleration by reason of the ballistic changes in the control system during the acceleration. Compensation (a) is produced by throttling the flow of mercury so that its displacement is proportional to the change in meridional speed. Compensation (b) is effected by the means shown, comprising a ring 36 pivoted on fore-and-aft trunnions 37 on the ring 32 and tilted through an angle proportional to the ship's speed by links 38, 39 connecting it to a worm sector 41 gearing with a worm 40 which is turned by a knob 42 either manually or from the ship's log. A lever 44 pivoted on the followup frame 6 in the E-W plane has at one end a roller 45 bearing on the ring 36 and is thus moved according to the ship's meridional speed. The trunnion 14b is carried by an arm 50 mounted on a pivot 51 on the ring 5 and carrying a worm sector 55 gearing with a worm 52 mounted on a plate 54 carried by the ring 5. The worm carries a sector 56 gearing with a sector 58 on a crank 57 rigidly secured to the lever 44. The trunnion is thus displaced proportionally to the meridional speed and tilts the level, the tilt being so adjusted in relation to the flow of mercury that the free surfaces of the mercury remain in the horizontal plane. To annul the torques which would be produced by the flow of mercurv, the level is re-balanced in its new position bv means of a weight 60 carried bv a lever 61 pivoted at 62 on the level, the arm 63 of the lever contacting with the arm 65 of a level pivoted on a pin 66 on the plate 54, the arm 67 of this lever being in contact with the sector 56. The remaining compensation is produced by twisting the filar 7 proportionally to the tilt of the level, the tail of the lever 44 being connected by links 70, 71 to a spindle 72 carrying a bevel pinion 74 gearing with a bevel wheel 75. This wheel 75 and the wheel 27 are connected to the torsion head through differential gearing contained in the box 76. The compensation in this case is tested by manual operation of the knobs 23, 25, 42, the knob 23 being quickly turned through the desired angle and left so turned for a stated time, while each of the knobs. 25, 42 is advanced by a number of equal steps.