272 



VII. DYNAMICS OF ROTATING BODIES. 



rotating top is not at in the direction of the motion of the apex, 

 but nearly at right angles thereto. (Exactly at right angles to the 

 motion of OH.} 



An ingenious application of this principle is found in the Howell 

 automobile torpedo, invented by Admiral Howell of the United States 

 navy. In this the energy necessary for driving the torpedo is stored 

 up in a heavy steel flywheel, weighing one hundred and thirty- five 

 pounds, and turning with a speed of ten thousand turns per minute. 



The axis of the flywheel 

 lies horizontally perpen- 

 dicular to the axis of 

 the torpedo (Fig. 86), thus 

 steadying the torpedo in 

 its course. If now any 

 force acts tending to 

 deflect the torpedo hori- 



se. zontally from its course, 



by means of a moment 

 about a vertical axis, the end of the axis of the disk moves vertically, 

 causing the torpedo to roll instead of yielding to the deflecting force. 

 The rolling is utilized, by means of a vertically hanging pendulum, 



to bring rudders into 

 action, and to cause 

 the torpedo to roll 

 back to its original 

 position, while main- 

 taining its course. 



A striking example 

 of the principle 

 enunciated above is 

 found in an inge- 

 nious top (Fig. 87), 

 spinning on its center 

 of mass, with its axis 

 rolling on various 

 curves constructed of 

 metal wire. No matter 

 what the shape of the wire, the axis of the top clings to it as if 

 held by magnetism, no matter how sharply the curve may bend. The 

 passing around sharp corners at a high speed, in apparant defiance 

 of centrifugal force, is extremely remarkable. The explanation of the 

 action is immediate, on the lines just laid down. The instantaneous 

 axis passes though the point of support (Fig. 88) and the point of 

 contact of the axis of the top with the wire. The wire, in fact, 



Fig. 87. 



