metal bottles fastened to the opposite faces of the gyro-casing, beside the control bottles. The upper ends of these " damping bottles " are connected by small pipes to an air-box A above the upturned air-nozzle Z, Fig. 171. Note that the connections of the air-pipes from the control bottles to the air-box, Fig. 169, are not the same as the connections of the air-pipes from the damping bottles to the air-box, Fig. 171. A needle valve V controls the speed of flow of oil from one damping bottle to the other.
The operation of the damping device is as follows: Suppose that the spin-axle is horizontal and at its maximum angular displacement to the east of the meridian. The north-seeking end is at a, Fig. 137. The oil is at the same level in the control bottles, and also in the damping bottles. As the earth carries the gyro-compass from the position X to the position Y, Fig. 170, the spin-axle tilts, oil is forced from the lower control bottle into the upper, and the spin-axle turns toward the meridian. When the meridian plane is