140. A CURIOUS GYROSCOPIC PHENOMENON. 
Bear in mind that there are two distinct energies ; that 
given to the disc by pulling thestring wound around its 
axle, and that coming through the belt from the driving- 
wheel. The former is disposed of partly by the friction 
of the air, and yet more by the friction at A and JB, 
where it passes into heat. 
The energy from the driving-wheel may be divided into 
two parts, the ordinary and the extra-ordinary. The or- 
dinary energy is that needed to overcome the resistance 
of the air and the friction at the various bearings, and 
by the belt. This is easily disposed of. It setsup mole 
cular action and changes into heat. 
This leaves only the additional energy which must be 
expended to make the ring revolve when the disc is in. 
motion, and which is not needed the moment the disc 
comes to rest. A part of this—only a small part—is 
used in causing an increase of friction on the two vertical 
pins, for the same tilting tendency that causes pressure 
at A and B produces a tendency in the ring itself to re- 
volve in its own plane, and hence produces a pressure on 
one side of each of the two vertical pins. But this ab- 
sorption of the energy is a matter of accident, as it were. 
There would be the same increase of horizontal motion 
from zero to maximum, and the same giving up of mo- 
tion from maximum to rest as before, for the friction on 
the bearings has no influence on that. And the amount 
of energy necessary to increase the movement of even a 
small fraction of a quadrant—or rather of two quadrants, 
for the process goes on in two opposite ones at once— 
from zero to twenty-five feet in one-eightieth of a second, 
7. é€., from 0 to 2,000 feet in a second, is certainly very con- 
siderable. If we might imagine energy to be something 
visible, we should see it taken up continuously in little 
buckets, as it were, as they pass from m (Fig. 1) to m’, 
and poured out as they pass on from m’ tom”. What. 
becomes of the energy poured out? One result is very: 
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