Experiment 8. Magic.
Find a large bottle made of clear glass, the neck of which will fit your solid rubber stopper.
Fill the bottle with water to overflowing, insert the balloon, and then the stopper.
Now press down hard on the stopper. Does the balloon sink in a most magical manner (Fig. 14)?
Release the stopper. Does the balloon rise in an equally magical manner?
FIG. 15
A BALLOON RACE