SOLIDS DEFYING GRAVITY. 



When the spinning gyroscope is supported at 

 one end and consequently the axis is turning round 

 the point of support, if we take a pencil, and, 

 holding it vertically, push the revolving knob 

 round a little faster than it is going of its own 

 accord, that end of the axis rises ; if we put 

 the pencil in front and retard it, that end sinks. 

 This is another form of that compromise be- 

 tween movements which we have seen to be 

 responsible for the turning movement in the 

 first instance. We can thus cause the free 

 end of the axis to rise or sink without any direct 

 pushing up or down, by simply hastening or 

 retarding the turning movement round the 

 point of support. 



This explains how it is that a top rises 

 to an upright position. 



When it is a little sloping, gravity pulls 

 at the outer that is, the upper end and so 

 causes the top to turn round the centre of 

 support, the point. But the point, rubbing 

 on the ground and so advancing in a circuit, 

 hastens this turning movement at the opposite 

 end of the axis. As we have seen, a hastening 

 of the turning movement causes the free 

 that is, the upper end of the axis to rise, 

 and so the top constantly tends to regain a 

 vertical position. 



35 



