When the Montgolfier brothers flew the first hot air balloon, word of this exciting event reached the king in Paris, who could immediately see the military potential. So he called for his chief scientific officer, M. Charles, and commanded him to produce a balloon. This considerable scientist racked his brains: "how could they have flown this contraption?" After a while he jumped up with the French equivalent of "Eureka." "They must be using this new gas called hydrogen, which is lighter than air!" he declared. So he proceeded to invent the hydrogen balloon, which is a totally different type of balloon.