On Water and Air. 
[August, 
to a certain extent with water ; and this makes the little 
figure heavier, and down it goes ; it sinks to the bottom of 
the jar. I now release the pressure, and the spring of the 
air within the ball ejedts the water that was forced into it, 
and the figure rises to the surface. 
Now let us make another experiment. I will press this 
covering, and at a certain point I will suddenly withdraw 
the pressure. What will occur ? Boyle’s spring of the air 
will again come into play. The air that is compressed in 
the hollow ball will suddenly relax itself, will suddenly ex- 
pand like a compressed spring, and will drive out the water 
Fig. 39. 
in the tail as before, and, inasmuch as the tail is curled 
round, the spring of the air will cause the little creature to 
pirouette. The spring of the air might be illustrated in 
fifty ways. For instance, here (Fig. 39) I have a small 
fountain. It is a spherical vessel, which has inserted into 
it a metal tube, E F, provided with a stopcock. It is about 
two-thirds filled with water. I have here a condensing 
syringe, which I will attach to the end of the tube at E, and 
by means of it will compress air into the fountain. The 
air will pass down the tube E F, and collect in the space 
