34^ THE CONQUEST OF THE AIR. 



For inflating- we employ in most cases ordinary eas from the 

 gas works. If therefore in this country we wish to go in for 

 ballooning-, we shall have to extend our gas works. Gas may, of 

 course, be bottled and transported in steel bottles, but this is 

 rather expensive. Usually this is done by the military. Such 

 bottles may also take the place of the ballast. The latter consists 

 as a rule of sand, in bags of 15 to 20 kg-s. weig-ht. The ballast is 

 of immense importance to an aeronaut and gives him a certain 

 freedom in his actions. Once all ballast has been dropped the 

 control has gone. For landing, at least two bags should be kept 

 in reserve, m order to prevent heavy impacts on the ground. At 

 the last moment, the bags are emptied. The upward pressure of 

 a cubic metre of ordinary gas is about 0.7 kg., hence a balloon 

 with a contents of 1,000 cubic metres has an upward pressure of 

 700 kgs. Its weight is about 250 kgs., so that 450 kgs. are left 

 for ballast, equipment and passengers. With such a balloon the 

 ballast should weigh not less than 10 sand bags of 15 kgs. each, 

 so that 300 kgs. are left for provisions, outfit and two passengers. 



During recent years the ordinary gas has often been replaced 

 by hydrogen, which gives an upward pressure of about i kg. per 

 cubic metre. This is of great importance. It means that a balloon 

 with 1,000 cubic metres content has an upward pressure of 1,000- 

 kgs., so that after deducting its own weight of 250 kgs., 750 kgs. 

 are left for ballast, equipment and passengers. 



When an ascent has to be made, the envelope is first spread 

 out, the net carrying the basket is then placed o^er it, the hose 

 from the gas mains is joined on, and gradually the balloon 

 becomes inflated. As the sphere becomes larger, sandbags ar^^ 

 hooked into lower meshes of the net. In the meantime the basket 

 is made ready. When the inflating is accomplished, the hose is 

 disconnected, and until the ascent commences the lower end of 

 the balloon is closed. The cage or basket is now joined to the 

 sphere and the conductor enters with his companions. The 

 weighing now commences. This is done by an expert and consists 

 in the determination of the number of sandbags to be carried. 

 Ready hands lift up sandbags and cage, others take bags away 

 until the expert thinks that the upward pressure is just right. 

 The lower end of the balloon is then opened again and the ascent 

 begins. 



The landing is carried out as follows : — When the ballast is 

 running short or other reasons make a landing necessary, the 

 aeronaut looks out for a suitable landing place, if possible near a 

 railway station or in a field where little damage can be done to 

 the crops. When such a spot is found, the conductor pulls the 

 valve line, which opens the valve at the top of the balloon and 

 allows the gas to escape. His companions keep the sandbags 

 ready, employing them if the descent is too rapid. Just before 

 the balloon reaches the ground the ripping gore is pulled off" which 

 empties the balloon almost instantaneously. The balloon is then 

 ]>acked together on a wagon and taken to the station. 



Ascents of this nature are on the whole connected with little or 

 no danger. As a matter of fact, in spite of the accidents we have 



