[Illustration: Diagram of apparatus as described in text]
Balls are supported aloft in the following manner. Underneath a
cauldron (fig. 45), containing water and closed at the top, a fire is
lighted. From the covering a tube runs upwards, at the extremity of
which, and communicating with it, is a hollow hemisphere. If we put a
light ball into the hemisphere, it will be found that the steam from
the cauldron, rising through the tube, lifts the ball so that it is
suspended.