Transportation in the Air 393 



400 cubic meters of gas. If hydrogen is used, how much of an addi- 

 tional load can it carry at sea level or where the air is of normal aver- 

 age density. It is necessary to know the densities of hydrogen and 

 of air. (What density was required in solving problems of objects 

 floating on water?) 



Air weighs 1.3 kilograms per cubic meter; hydrogen, 0.09 kilogram 

 per cubic meter. Thus we have the following data: 



Weight of solid materials of balloon 150 kilograms 



Weight of hydrogen 0.09 k. x 400 (cubic meters) . . 36 kilograms 



Total weight ....'. 186 kilograms 



Weight of air displaced, 400 cubic meters by gas . . 



1 cubic meter by solids 

 401 x 1.3 (k. per m. 3 ) ... 521 kilograms 



Buoyant force of air displaced 521 k. 



Weight of balloon, etc 186 k. 



Unbalanced force upwards 335 kilograms 



How heavy a load can the balloon carry and still float ? If you desire 

 to change these numbers to English units, you may take one kilogram 

 as equivalent to 2.2 pounds ; and one cubic meter equivalent to about 

 1.3 cubic yards. 



181. Dirigible balloon. Although the gas balloon has not 

 proved to be commercially important, it has made possible a 

 better knowledge of the world in which we live. But a new step 

 has been taken in the construction of airships, which utilizes the 

 internal combustion engine, electric ignition, and self-starting 

 devices. Drifting with capricious air currents at high altitudes 

 is not especially profitable ; steering and propulsion are in- 

 dispensable. Steering in the upper air is not, however, so simple 

 as steering on land or sea with a motor vehicle ; starting from 

 and returning safely to the earth, both being hazardous to men 

 and machinery, must be mastered. The airship, moreover, 

 must have stability ; that is, it must keep right side up, and be 

 at all times under the control of the aeronaut. 



It was early found practicable to combine without much risk 

 of explosion the gas engine with the hydrogen balloon. The 

 achievements of Santos Dumont in the years 1901-02 proved the 

 utility of the petrol or gasoline engine for this purpose. The 



