126 AN EMPIRICAL STUDY OF GYRATING BODIES. 



The effect of accelerating the gyration, or horizontal 

 movement, is beautifully shown by the following easy 

 experiment : 



Suspend from the ceiling by a stout cord, a balanced 

 gyroscope, its axle being horizontal when at rest. At- 

 tach crosswise to the cord, a few inches above the in- 

 strument, a small stick, so as to be able easily and 

 quickly to twist the cord to the right or left. Now set 

 the wheel to revolving. The instrument will stand per- 

 fectly still. Twist the cord so that its torsion tends to 

 make the gyroscope move in the same direction as the 

 bottom of the wheel. It will begin to rise. Stop the 

 torsion, and the rising ceases. Twist the cord the other 

 way, the instrument tilts down. Then move the weight 

 on the arm so that the wheel side becomes the heavier, 

 one or two pounds, or more, if you please. Again, set the 

 wheel to revolving. The gyroscope will at once start 

 off horizontally, and also begin to tilt downward. 

 Twist the cord as before, it will tilt down less rapidly. 

 Twist the cord a little more, the gyroscope will cease 

 falling. Twist it yet more, and the gyroscope will be- 

 gin to tilt upwards. 



We are now, I think, in a position to answer intelli- 

 gently the question which we passed over : Why does 

 the gyroscope in actual operation fall so much less than 

 is indicated by the formula, ve J d s s . |l2a ? Why, e. g., does 

 it, in fact, fall only one one-hundredth of an inch, when, 

 apparently, it should fall four or five inches ? The 

 reason is found in that acceleration of the horizontal 

 movement. 



If the acceleration continued at the rate at which it 

 commences, it would cause the gyroscope to rise to a 

 vertical. But when it begins to resist gravity, gravity 

 produces less and less downward movement, and the 

 less there is of this the less is the acceleration. Hence, 



no 



