aerostats of the elongated form introduced by Henry Giffard, the
machines of Dupuy de Lome in 1872, of the Tissandier brothers in
1883, and of Captain Krebs and Renard in 1884, yielded many important
results. But if these machines, moving in a medium heavier than
themselves, maneuvering under the propulsion of a screw, working at
an angle to the direction of the wind, and even against the wind, to
return to their point of departure, had been really "guidable," they
had only succeeded under very favorable conditions. In large, covered
halls their success was perfect. In a calm atmosphere they did very
well. In a light wind of five or six yards a second they still moved.
But nothing practical had been obtained. Against a miller's wind--
nine yards a second--the machines had remained almost stationary.
Against a fresh breeze--eleven yards a second--they would have
advanced backwards. In a storm--twenty-seven to thirty-three yards a
second--they would have been blown about like a feather. In a
hurricane--sixty yards a second--they would have run the risk of
being dashed to pieces. And in one of those cyclones which exceed a
hundred yards a second not a fragment of them would have been left.
It remained, then, even after the striking experiments of Captains
Krebs and Renard, that though guidable aerostats had gained a little
speed, they could not be kept going in a moderate breeze. Hence the
impossibility of making practical use of this mode of aerial
locomotion.

With regards to the means employed to give the aerostat its motion a
great deal of progress had been made. For the steam engines of Henry
Giffard, and the muscular force of Dupuy de Lome, electric motors had
gradually been substituted. The batteries of bichromate of potassium
of the Tissandier brothers had given a speed of four yards a second.
The dynamo-electric machines of Captain Krebs and Renard had