830. Why do balloons ascend in air?
Because the air or gas which they contain is specifically lighter than the atmosphere; the atmosphere, therefore, forces itself underneath the balloon, by its own tendency towards the earth, and the balloon is thereby raised upwards. A balloon is but a larger kind of bubble, made of stronger materials.
831. Why does an air-balloon become inflated when the spirit set upon the sponge is lit?
Because the heat of the flame, and the burning of the spirit, A, create a volume of rarefied, or thin air, which inflates the balloon, and makes it specifically lighter than the surrounding medium.
"A wise son heareth his father's instruction."—Proverbs xiii.
832. Why do balloons sometimes burst when they ascend very high?
Because, as they get into the thinner air, which exists at high altitudes, the gas within them expands, and the coating of the balloon is burst asunder.