92 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK i. 



whole surface of the balloon covered with the net, arid gives both to 

 the car and to the travellers a steadiness absolutely indispensable. 



To inflate a hot-air balloon, it is simply necessary to place a 

 stove or vessel filled with burning materials under the opening ; the 



FIG. 5C. Gas-balloon. 



heated air rises into the envelope, and by degrees its elastic force 

 stretches the sides and makes them take a spheroidal form. When 

 Montgolfier made his first experiments, he believed that electricity 

 took part in the phenomenon of ascension, whilst it was the specific 



