Balloon

Balloon. A general account of the historic development of aerial navigation has been given in the article Aeronautics. It is necessary here to explain the general conditions to be followed in the design of balloons, and the directions in which improvement may be sought. Archimedes' principle tells us that the entire weight of a balloon and its appendages must be less than that of the air displaced. Hence some substance specifically lighter than air, such as hydrogen gas, must form part of the balloon. The lighter the gas employed, the smaller the volume of it required to raise a given load. The above principle, again, assigns a limit to the height a balloon can rise, for it evidently cannot be sustained at a height where the density of the atmosphere is less than that of the enclosed gas.

A definite quantity of this gas must be contained in an envelope of suitable dimensions and strength. As the balloon rises, the external pressure of the atmosphere diminishes, thereby increasing the tendency of the enclosed gas to burst its envelope. The spherical-shaped envelope is the strongest, and has been generally adopted. When translation from place to place is effected by air currents simply, this form is very convenient; but when the air-vessel is intended to provide its own means of locomotion, a shape is required that shall combine strength with small resistance to its motion through the air. Such we have in the torpedo-shaped aerostat.

Concerning the motive power necessary to make our vessel more or less independent of the various air-currents, some means for the compact storage of energy readily convertible into motion must be available. Electric accumulators may for instance drive a quick-speed motor that shall work a screw-propeller. Already such an arrangement has been successfully tried, and inasmuch as the questions of compact electrical storage batteries and of compact motors are of great importance in other fields, we may hope for a direct application of these to aerial navigation. In the above, definite distinction is made between a balloon and a flying-machine (q.v.). The former can remain motionless in the air by reason of its lightness; the latter requires expenditure of energy to prevent its falling.