An elementary treatment of the theory of spinning tops and gyroscopic motion, by Harold Crabtree.

INTRODUCTORY CHAPTER

11

Experiment 2. If the wheel is taken out of its bearings at
Y, Y', and the framework held in the hands at X, X', a violent
attempt tQ tilt it about Y'Y will, unless proper care is taken,
result in the wheel wriggling out of the hands altogetherfor the same reason that when properly mounted just now
it turned about ZZ'.
It is clear that an opposite direction of spin or any attempt to
tilt in the opposite direction, produces an opposite direction of
turning about ZZ'.
Experiment 3. Let us now take the gyroscope when the
wheel is not spinning, and its axle XX' is inclined at an angle
to the vertical as in Fig. xxIII., the screw at Z not being
clamped.
If the pedestal ZZ' is held in the hand and slowly swung
round, it will be found that XX' turns round about the vertical
and points in the same direction as
the hand. But let a spin be given to X
the wheel, and it will be seen at once
that, though the hand revolves round
the body, XX' remainiss always pointing in the same direction in which it
pointed originally.*
This stability of the axle of the X
gyroscope may be employed to prove
the rotation of the earth. For suppose the spin is maintained during a Z
period of several hours by means of
electric power, and that the gyroscope
is set down in a room with its axle
pointing to some particular object in (
the room. After a few hours it will
be found that the axle no longer
points to that object; showing, not
that the axle has changed its position
in space, but that the room is in a --
different position in space owing to
the rotation of the earth. FIG. XXIII.
Thus, if the axis is placed horizontally pointing due east, six hours later it will be pointing south
(and upwards), while after another six hours it will be pointing
due west (and horizontally).
Experiment 4. Now, while the wheel is still spinning, let the
turning movement be given to the hand when the screw at Z
has been made fast. The gyroscope at once sets itself with the
* The friction may not be quite negligible though very nearly so. The
frictional couple at Z is probably sufficiently large to turn the frame YY' round
when the wheel is not spinning, but totally inadequate when it is spinning. So
much as is appreciable tends to turn it about Y'Y, as will be seen later.