42 AERIAL NAVIGATION. 
elongated balloon (fig 1) which he inflated with coal gas. 
Suspended beneath it by cords was a longitudinal shaft, 
at the end of which was a triangular sail that could be 
turned about an axis and made to serve the purpose of 
arudder. Below the shaft was a framework of wood 
supporting a small steam engine, whose piston gave 
motion to a screw propeller. He ascended with this to 
a height of five thousand feet and succeeded in making 
ys 
| mmenell 
FIG. 1. 
perceptible headway against a strong breeze, besides 
changing direction at will. Aerial navigation was thus 
proved to be possible, but this method was abandoned 
on account of the great danger, similar to that which 
had caused the death of PilAtre de Rozier, and the dif- 
ficulty in keeping the weight of the balloon constant. 
Giffard attained a speed estimated to be about nine 
miles an hour. 
