large empty bag is made with a wide mouth below like a pitcher upside down, and in the mouth is placed a bunch of cotton which is soaked with ether and then set on fire. The air in the balloon is heated by the fire and becomes lighter than the cold air outside, and the balloon rises like a bubble in water, and it floats up in the air until it reaches atmosphere so rare as to be lighter than the heated air.
Almost a century ago some Frenchmen—the Montgolfier brothers[1] invented the hot air balloon. They made a bag of cloth and paper and filled it with hot air; it floated. Then they made another still larger, attached a ram, a cock, and a duck to it and sent it up. The balloon ascended and returned successfully. Then they attached a small boat to it, and a man took his place in the boat. The balloon went up so high that it was lost to sight; it floated off and then came down without injury. Then they invented the method of inflating balloons with hydrogen, and they kept going higher and more rapidly.
In order to make a balloon ascension a basket is attached to the bag, and two, three, and even as many as eight men accommodate themselves in it, taking with them food and drink.
In order to regulate the movements of the balloon up and down at will, a valve is constructed in the balloon, and the aëronaut[2] can open it or shut it at his own pleasure. If the balloon rises too high, and the aeronaut wishes to descend, he opens the valve, the gas escapes, the balloon contracts, and begins to sink. Moreover, he always carries bags of sand. If a bag is thrown out, the balloon becomes lighter, and it rises. If the aëronaut wishes to come down, and sees that it is not a fit place for landing,—on account of a river or a forest,—then he empties out some sand, and the balloon becomes lighter and rises again.
