Page:Popular Science Monthly Volume 75.djvu/41

Rh contained in a solid steel disk 2 feet thick, 10 feet in diameter and rotating at a speed of 144 revolutions per minute; and therefore this amount of rolling torque continued for one tenth of a second would bring the axle of such a wheel into a horizontal position so that any further continuation of the torque would cause the ship to roll.

The rolling motion of a ship, however, is largely an oscillatory motion which is slowly built up by a succession of waves in synchronism with the proper period of rolling motion, and excessive rolling may therefore be prevented by an action which tends to hinder the oscillations by friction. A very considerable amount of frictional damping may be produced by a moderately small gyrostat arranged as shown in Pig. 32 (plane of paper in Pig. 32 is a vertical plane containing the keel of the ship). In this case the rolling motion of the ship causes the pendant wheel and axle to oscillate to and fro in the plane of the keel, and these oscillations are hindered by the motion of a piston in a dash-pot as indicated in the figure.

Before discussing the Brennan gyrostatic mechanism for maintaining the equilibrium of a monorail car, let us consider the action of the apparatus shown in Figs. 33 to 36, a gyrostat wheel mounted in a frame aa which in turn is pivoted in a larger frame BB, the whole

being supported upon two legs, one behind the other, as seen in the figures. Standing in the position shown in Fig. 33, the framework is acted upon by the unbalanced pull of the earth which produces a torque; the spin-momentum which is continually produced by this torque is absorbed by a precessional motion P of the gyrostat wheel as it