[Illustration]
This amusing pneumatic toy consists of a figure made of glass or
enamel, and so constructed as to remain suspended in a glass jar of
water. An air-bubble, communicating with the water, is placed in some
part of the figure, shown at _m_, near the top of the jar, A, in the
engraving. At the bottom, B, of the vessel is a bladder, which can be
pressed upwards by applying the finger to the extremity of a lever, _e
o_, when the pressure will be communicated through the water to the
bubble of air, which is thus compressed. The figure will then sink to
the bottom; but, by removing the pressure, the figure will again rise,
so that it may be made to dance in the vessel, as if by magic. Fishes,
made of glass, are sometimes substituted for the human figure. A common
glass jar may be used for this experiment, in which case the pressure
should be applied to the upper surface, which should be a piece of
bladder, instead of being placed at the bottom, as shown in the figure
engraved.