THE CONQUEST OF TIME AND SPACE 



ing the spindle E firmly, and then whirled the gyrostat 

 about at arm's length, the axis O A would at once be 

 forced to take an upright position. If your hand whirled 

 to the right, the point A would rise; if your hand whirled 

 to the left, the point A would go down; the principle 

 determining this motion in either case being that the 

 direction of whirl of the gyroscope must correspond to 

 the direction of curve given to the apparatus as a whole 

 by the motion of your arm. 



Exactly the same principle applies to the Brennan 

 gyroscope when the car to which it is attached goes 

 about a curve. The frame pivoted at Z> £ revolves only 

 within a limited arc, and then becomes fixed, and so the 

 axis O F tends to tip upward when the car rounds a 

 cur\'e. If only a single gyroscope were used, this would 

 tend to make the car tip in opposite directions, accord- 

 ing to whether the car is going forward or backward, 

 and the tip might be dangerous in going about a curve, 

 as Mr. Brennan found to his cost in his earlier experi- 

 ments. But when the two gyroscopes, revolving in 

 opposite directions, are linked together, the action of 

 one balances that of the other, and their joint effect is 

 always to make the car lean in at a curve, which is 

 precisely what it should do to ensure safety. More- 

 over, the two linked gyroscopes keep their planes 

 of revolution parallel to the rail, as is essential to 

 their proper action, and as a single gyroscope would 

 not do. 



The balancing action of the gyroscope seems no whit 

 less remarkable after it is explained. It should be said, 

 however, that the force exerted by the mechanism is not 



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