On September 19, 1783, there was big excitement at Versailles in France. The Montgolfier brothers were going to try to dispatch a balloon up into the sky. They had tried a balloon a few months before, and it had worked. Now they were going to try again before the King. And this time the balloon was to have passen-gers—a rooster, a sheep, and a duck were to ride in a basket hanging from the balloon.
The balloon was made of linen and was open at the bottom. Ropes held it in place over a fire of straw. A mixture of smoke and hot air rose from the fire into the balloon. The mixture was lighter than the cool air round about.
The ropes were loosened, and the balloon rose. Up and up it went. When the smoke and hot air cooled, the balloon carne down.
Soon there were balloons that could carry people. Many of these balloons were filled with hydrogen, the lightest gas known.
The first balloons were at the mercy of the wind. The passengers could not guide them. But they could make them go up or down. They carried bags of sand or some-thing else heavy for ballast. To go higher, they threw ballast overboard. To come down, they let some gas out of the bag.
More than 100 years ago the first dirigibles were built. By means of engines, propellers, and rudders they could be made to go in any direction. Some of the later dirigibles had a framework of aluminum. These were called zeppelins in honor of Count Ferdinand von Zeppelin, who invented them. In 1929 a zeppelin flew all the way around the world. But in 1937 a terrible accident put a stop to travel in zeppelins. A big zeppelin, the "Hindenburg," burned up just as it finished a flight from Germany to the United States. A spark had set fire to the hydrogen in its bag.
Helium is a gas that will not burn. It is not as light as hydrogen, but it is much safer. The balloons of today, if they carry people, are filled with helium.
