278 Our Surroundings 



The Balloon. For centuries, man has sought to make some 

 form of craft that would float in the air. These efforts came 

 to nothing until about 1783, when the Montgolfier brothers made 

 the first balloon of which we know. They made a bag some- 

 what more pointed than the modern balloon and filled it with 

 heated air. It went up and satisfied them that they were on 

 the right track. In further experiments they attached a basket 

 to the bag and sent up a lamb, a duck and a rooster. These 

 were carried up and then came safely back to earth. Later, 

 with the balloon held captive by ropes, first one person and 

 then two ascended and remained aloft for nearly half an hour. 

 As in all fields of science, steady improvements have been made 

 in balloons and other air craft. 



A standard balloon consists of an enormous bag of cotton 

 or silk cloth, coated with a rubber preparation to prevent leak- 

 age of gas. Over the bag is carefully fitted a rope net to the 

 lower strands of which a light-weight basket is attached to carry 

 passengers. 



The power of the balloon to lift weights depends upon the fact 

 that it is filled with gases which are lighter than air. Consequently, 

 they tend to rise and are able to lift a weight nearly equal to the 

 difference between the weight of the gases in the balloon and the 

 weight of a corresponding volume of air. Originally, hot air, 

 which is lighter than the ordinary air, but which cools rapidly, 

 was used. Then coal gas was employed, and after that hydrogen. 

 These two gases are highly dangerous because extremely inflam- 

 mable. Helium gas, non-inflammable and almost as light as hydro- 

 gen, is now being used to some extent, although the supply is 

 limited. 



Before a balloon starts on a flight, the collapsed bag is con- 

 nected with the gas tanks and gas is admitted until the bag is 

 partially inflated and begins to tug at its moorings. Then the 

 basket is attached and the mooring ropes are freed. The bag 

 becomes fully inflated as the balloon mounts, because the atmos- 

 phere becomes lighter and the balloon gas tends to expand rapidly. 

 When the air becomes so light as to equal the lightness of the gas 

 in the balloon, plus its load, the balloon stops rising. It may be 



