PLACE a cauldron over a fire: a ball shall revolve on a pivot.
A fire is
lighted under a cauldron, A B, (fig. 50), containing water, and covered
at the mouth by the lid C D; with this the bent tube E F G communicates,
the extremity of the tube being fitted into a hollow ball, H K. Opposite
to the extremity G place a pivot, L M, resting on the lid C D;
and let the ball contain two bent pipes, communicating with it at the
opposite extremities of a diameter, and bent in opposite directions, the
bends being at right angles and across the lines F G, L M. As the
cauldron gets hot it will be found that the steam, entering the
ball through E F G, passes out through the
bent tubes towards the lid, and causes the ball to revolve, as in the
case of the dancing figures.