When the news of this event reached Paris a professor of physics named Charles suggested that hydrogen, being much lighter than air, would raise the balloon without the use of fire. By a popular subscription funds were raised to defray the expenses of securing enough iron filings and sulphuric acid to generate the hydrogen necessary to fill a balloon of 22,000 cubic-foot capacity. On the 27th of August, 1783, a flight was attempted. The big bag arose without mishap and disappeared in the clouds. Three quarters of an hour later it landed in a field fifteen miles away much to the astonishment of the villagers thereabout who gathered around the strange bobbing monster with mingled fear and curiosity. One of the number, more daring than the rest, advanced and shot the balloon, whereupon the crowd closed in and tore it to pieces with their pitchforks. In November of the same year the Montgolfier brothers built a balloon 48 feet in diameter and 74 feet high, and Jean François Pilatre de Rozier, a professor of natural history, made several ascents with the balloon held captive. Then, in company with the Marquis d’Arlandes, the balloon was cut loose and the balloon voyage was undertaken. Below the car of the balloon was an iron vessel in which a fire was maintained to furnish the heated air. The aeronauts each carried a bundle of fuel to feed the fire and a wet sponge to extinguish sparks that might ignite the bag. Despite this precaution a number of holes were burnt in the envelope, but nevertheless the flight was successful and the daring voyagers came to earth without mishap after a short journey. M. de Rozier’s career as an aeronaut was a short one. The first man to be carried up in a balloon, he was also the first balloon victim. He undertook to combine the Montgolfier and the Charles systems by building a balloon that employed both the hot air and the hydrogen principles, but the balloon took fire and De Rozier with his companion, the Marquis de Maisonfort, were both killed. Two months after De Rozier’s first balloon ascension a flight was made at Lyons in a huge fire balloon which carried seven passengers. This big bag was 100 feet in diameter and 130 feet high, with a capacity of 590,000 cubic feet. The invasion of the air was now well under way, although for a time it made little real progress. Owing to the danger of fire, hot air eventually gave way to hydrogen and later to coal gas, which, although it did not have half the lifting power of hydrogen, possessed the advantage of being much cheaper. THE WEIGHT OF AIR