ture of his buoyant medium in the balloon. He
calculated that a balloon, 50 feet in diameter and 150 feet in length,
with a vertical surface in front and a horizontal surface behind, might
be navigated at a speed of ten miles per hour, and in actual tests at
Brunn he proved that a single rise and fall moved the balloon three
miles against the wind. His ideas were further developed by Lebaudy in
the construction of the early French dirigibles.

According to Hildebrandt,[*] the first sailing balloon was built in 1784
by Guyot, who made his balloon egg-shaped, with the smaller end at the
back and the longer axis horizontal; oars were intended to propel the
craft, and naturally it was a failure. Carra proposed the use of paddle
wheels, a step in the right direction, by mounting them on the sides
of the car, but the improvement was only slight. Guyton de Morveau,
entrusted by the Academy of Dijon with the building of a sailing
balloon, first used a vertical rudder at the rear end of his
construction--it survives in the modern dirigible. His construction
included sails and oars, but, lacking steam or other than human
propulsive power, the airship was a failure equally with Guyot's.

[*] Airships Past and Present.

Two priests, Miollan and Janinet, proposed to drive balloons through the
air by the forcible expulsion of the hot air in the envelope from the
rear of the balloon. An opening was made about half-way up the envelope,
through which the hot air was to escape, buoyancy being maintained by a
pan of combustibles in the car. Unfortunately, this development of the
Montgolfier type never got a trial, for those who were to be spectators
of the first flight grew exasperated at successive delays, and in the
end, thinking that the balloon would never rise, they destroyed it.

Meusnier, a French general, first conceived the idea of compensating
for loss of gas by carrying an air bag inside the balloon, in order
to maintain the full expansion of the envelope. The brothers Robert
constructed the first balloon in which this was tried and placed the
air bag near the neck of the balloon which was intended to be driven
by oars, and steered by a rudder. A violent swirl of wind which was
encountered on the first ascent tore away the oars and rudder and broke
the ropes which held the air bag in position; the bag fell into the
opening of the neck and stopped it up, preventing the escape of gas
under expansion. The Duc de Chartres, who w