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

INTRODUCTORY CHAPTER

7

rise up on their longest axis, in which position they remain
spinning violently, though otherwise stationary on the road.
What seems at the present time to be a favourite form of whiptop with children in the streets is an instance of the same thing.
It is, roughly, in the shape of a large acorn with a thick cap
to it. In whatever position it is first put down on the road
violent lashing will always make it rise on to its longest axis,
and continued lashing causes it to continue to spin in that
position.
Celts. Figs. xi., xiI., xiii. (see Plate I.) represent three
celts, stone implements used in times past by primitive man for
cutting or cleaving, and now discovered from time to time in
ancient barrows (Latin: Celtis, a chisel).
They provide typical instances of the curious phenomena
exhibited by all smooth celts when spun on a smooth horizontal
surface (such as a sheet of glass).
Let us perform the same experiment on each in turn and
note the results.
In each case, the stone being considered at rest, GAB is a
horizontal section (very roughly elliptical) through the centre
of gravity G, and GA, GB, GC are mutually at right angles.
FIG. XI. (See end of book.)
(a) If a vertical downward tap be applied at A the stone
will rock about GB, and if the tap be applied at B the
rocking will be about GA.
(b) If spun about the vertical GC the stone will continue
to spin steadily about GC until brought to rest by friction.
These results are what we should ordinarily expect. But
now let us consider the other two celts.
FIG. XII.
(a) When a vertical downward tap is applied through A
the stone oscillates and then begins, almost immediately, to
rotate from A to B; but if the tap be applied at B, the
stone, after a moment's oscillation, begins to rotate from B
to A.
(b) If spun in either direction it will begin to oscillate and
gradually reverse its direction of spin.
FIG. XIII.
(a) A vertical downward tap through A or B sets the
stone rotating in the direction from A to B.
(b) If spun in the direction A to B it will continue to spin
steadily in that direction; but if spun in the direction B to A
the stone will oscillate violently and eventually reverse its
direction of spin, i.e. will spin in the direction A to B.