USEFUL ARTS. 



CHAPTER XL 



AEROSTATICS. WEIGHT OF AIR. EXPANSION BY HEAT. 



Ascent and Descent. The Balloon and the Parachute. Description of the 

 Balloon. The Montgolfier Balloon. Causes of its Abandonment. The Gas 

 Balloon. Hydrogen Gas and its Manufacture. The Gossamer Spider. 

 Reasons of its Ascent and Descent. Many Species of Gossamers. Descrip- 

 tion of the Parachute. Its Mode of Action. A Balloon converted into a 

 Parachute. Toy Parachutes. Natural Parachutes. The Dandelion Seed 

 and its Structure. The Flying Squirrel. The Flying Monkey. Flying 

 Mice and Flying Opossums. The Flying Dragon and its Pseudo-wings. 

 The Flying Frog. Weight of Air. Pressure per Square Inch. The Air 

 Ocean and its Storms. Principle of Air-currents. The Sun, the Earth, and 

 the Air. Ventilation of Mines. Choke-damp and Fire-damp. The Air- 

 shafts. Chimneys of Factories. The Steam-blast. The Barometer, and 

 Mode of its Construction. Water and Mercury. Sucking Eggs and Sugar- 

 cane. Expansion of Water and Metals by Heat. The Thermometer. 

 Wheel-making. 



AEROSTATICS. 



T7E will begin this chapter with the only two modes at 

 present known by which man can ascend from the earth 

 or descend to it with safety, namely, the Balloon and the 

 Parachute, the latter being generally attached to the former, 

 and detachable at pleasure. 



The Balloon is, in fact, as its name imports, a large, hollow, 

 air-tight ball, filled with some substance lighter than ordinary 

 air. The original Balloons by Montgolfier were filled with 

 heated air exactly like our toy fire-balloons. Just as the 

 supply of hot air is kept up in them by a sponge dipped in 

 lighted spirits of wine, so in Montgolfier' s balloons the same 

 object was attained by straw which was kept continually 

 burning in a grate. 



There were, however, two disadvantages about this plan. The 

 first was the great danger of fire, which on one occasion did 



