38 THE POPULAR SCIENCE MONTHLY 



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 



Fig. 35. Fig. 36. 



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 preces- 

 sional 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 preces- 

 sion 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 0, and the two gyrostat wheels are 



