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

12

INTRODUCTORY CHAPTER

axis XX' vertical as in Fig. xxiv., and when once this position
has been gained a further swing of the hand in the same
direction finds it in stable equilibrium: but if we check or
reverse the swing we find that the equilibrium is unstable,
and if the checking or reversal be sudden, the gyroscope
will turn a complete somersault I
FIG. XXIV. FIG. XX
FIc. XXIV. FIG. XXV.
Fig. xxv. represents the same gyroscope taken to pieces
and put together in another form. Here the weight of the
instrument itself, when no extra weight is suspended, instead
of tilting the gyroscope over, causes it to turn about ZZ' as
before; and it will be found that if the rate of turning be
hurried by the application of a horizontal force to the frame
of the gyroscope, then the centre of gravity of the instrument
will at once begin to rise.
The following pages will be devoted to discussing the phenomena described in this chapter, and to explaining why the
gyroscope appears to defy all the recognized laws of gravity.
The same principles account for an elongated bullet, when fired
from a rifle, always " drifting" to the left-hand side, as also in part
for the gyrations of a boomerang, but not in general for the
swerving of a sphere, as for instance a cricket ball or a " sliced"
golf ball. In order to get a clear idea of the subject it will first
be necessary to master a few elementary principles in Dynamics
which are discussed in the first two chapters of this book.