Page:Popular Science Monthly Volume 75.djvu/42

38 turns from the position shown in Fig. 33 to the position shown in Fig. 34, and the reaction of this precessional motion produces the two forces FF, Fig. 33, which keep the frame from falling over. When the gyrostat wheel reaches the position shown in Fig. 34, however, the precession ceases and the frame-structure falls over. Standing in the position shown in Fig. 35, 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 the precessional motion P' of the gyrostat wheel as it turns from the position shown in Fig. 35 to the position shown in Fig. 36, and the reaction of this precessional motion produces the two forces F'F', Fig. 35, which keep the frame from falling over. When the gyrostat

wheel reaches the position shown in Fig. 36, however, the precession ceases and the frame-structure falls over. Suppose the handle h in Figs. 33 and 34 to be forcibly turned in the direction of the precessional motion P. This hastened precession causes the reactions FF to be more than enough to hold the inclined frame in position, and the result is to bring the frame into a vertical position, or, if the precession is hastened sufficiently, to throw the frame-structure over into the reverse position as shown in Fig. 35, thus starting the reversed precession P'. This hastened precession is the essential feature of the Brennan gyrostatic mechanism and it is brought about automatically as explained in the following discussion.

The essential features of the Brennan mechanism are shown in Fig. 37. The car body BB' supports a rocker-axle which is parallel to the rail or rope W upon which the car stands. A steel frame FFFF is supported upon the rocker-axle O, and the two gyrostat wheels are