This seems to be a plain wooden ball with a hole bored in its center,
through which a string is passed. The ball will move lightly up and
down this cord, but let some one who knows the trick take the string
in his hand and it becomes quite a different matter; the ball will
move quickly, or slowly, at command, and, if told to do so, will stand
still until ordered to move on again.
The reason for this peculiar behavior is that inside the ball there
are two holes, one of which is quite straight, while the other is
curved, and turns out of the straight hole.
It is through this curved passage that the cord is passed, and you
can easily see that to regulate the movements of the ball, it is only
necessary to hold the string more or less tightly. If you hold the
cord perfectly tight, the ball will not be able to move at all. The
ball can be purchased at any top shop.
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