Fig. 30.—AIR-BALLOON.
Fig. 31.—PAPER PARACHUTE.
833. Why does the gas of balloons expand in thin air?
Because the air exerts a less amount of pressure upon the air or gas contained in the balloons.
834. Why do parachutes fall very gradually to the ground?
Because the air, coming in contact with the under surface of the expanded head of the parachute resists its downward progress.