170 GYROSTATIC BALANCE. 
give facility in handling the instruments, and, when de- 
sirable, movable weights can be attached to counter- 
balance, to any extent, the wheels. You have noticed, 
probably, that the rod on the lower gyroscope is bent out 
of line of the axle. This was done to permit the wheel 
to fall lower than it otherwise could. 
- I now wind a string on each axle in such a way that 
the direction of the resulting rotation is the same as in 
Sir William’s diagram, and set both going. I will then 
place the instrument on the upright shaft, and leave it to 
itself. If his prediction is right there will be no rotation 
around the upright. 
You see there is rotation. He says the lower end 
should fall, to a certain point, and there remain at rest. 
You see it rises till its axis points to the zenith. (Fig. 4.) 
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Fig. 4 
MMMM MM OO 
I will repeat the experiment. You see the results are 
the same. 
I now wind the strings so that the wheels revolve in 
opposite directions, and place it in position as before. 
The lower gyroscope instantly drops toits lowest possi- ° 
ble place, I raise it, but it at once goes back. 
At first it would seem as if there should be no moment 
of momentum. In fact while the lower gyroscope is 
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