CHARLES B. WARRING, 137 
_vious experiment—when I did not set the disc to revolv- 
ing—the horizontal rotation continued for a considerable 
time after the clutch was released. Butnow the machine 
acts as if it had no momentum, or it would be better to 
say, that it behaves as if the air had suddenly become 
highly viscid. 
Fourth Experiment—We have again the two rotations 
in planes perpendicular to each other, and both rotations 
_very rapid. In experiment 3, the ring was connected 
with the driving-wheel only a few seconds, and then re- 
leased ; now the connection is kept up, and I continue 
to turn the driving-wheel as rapidly as I can against 
the resistance which the gyroscope offers. This is very 
decidedly felt, and throws the instrument and the table 
on which it stands into a violent tremor, rattling what- 
ever happens tobe on it. After a little—from twenty to 
sixty seconds—the resistance seems exhausted, the tremor 
and rattle cease. No effort is now necessary to keep up 
the rapid horizontal rotation. I stop the apparatus as 
quickly as possible, and find that the disc has come to 
rest. It ought to have run several minutes longer. 
These results give rise to three questions: 
1. What causes the strong resistance ? 
2. What causes the disc to come to rest so much sooner 
in experiment 4 than in experiment 1 ? 
3. What becomes of the large amount of energy ex- 
pended in overcoming the resistance when the two rota- 
tions are going on simultaneously ? | 
As to the first question—the strong resistance. Sup- 
pose the instrument in operation, and the movements to 
be indicated by the arrows in Fig. 1, and very rapid— 
twenty revolutions or more in a second. Fasten your 
mental vision upon a molecule, m, at the lowest point in 
the disc, and in the line of the vertical axis. At that in- 
stant it will be absolutely at rest in reference to the hori- 
zontal rotation. 
87 
