[Illustration: Diagram of apparatus as described in text]
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.