FL YING-MA CHINES. 



Of course we may provide our balloon with wings or propeller, and 

 fly as the birds fly. This has been and continues to be a favorite com- 

 bination with our inventors. One patented in this country in 1880 has 

 been chosen as an illustration. The balloon, oblong in shape and 

 divided for safety into compartments, supports a car containing the 

 propelling machinery, and also a gas-generator to make up such loss 

 of hydrogen as may occur. Two immense rudders steer tbe machine. 

 It is propelled by four paddle-wheels, which would act, one would 

 think, very much as the wheels of our river-steamers would act, if 

 totally immersed in the water, and would be about as likely to drive 

 the balloon backward as forward. 



Generally, however, in machines of this class the propeller is one 

 gigantic screw, or a number of screws, and the balloons have a variety 

 in shape and grouping which is quite remarkable. 



It is strange that people have not realized that a thing necessarily 

 so big and light as a balloon can not be made strong and durable 

 enough to stand the pressure of the wind at comparatively low ve- 

 locities. Floating with the current, the velocity would have no de- 

 structive effect ; but brought into opposition to this current, or forced 

 at any great speed through the air, the resistance would be much 

 greater than a silk bag could safely stand. 



It may be well here to refer to a table giving the relation of press- 

 ure to velocity of air, experimentally determined and verified time 

 and again — results very important in the study of flying and flying- 

 machines : 



Now let us suppose that a balloon only forty feet in diameter should 

 resist the pressure of wind blowing at the rate of twenty miles an hour, 

 or, what is the same thing, that the balloon should be traveling through 

 still air at this speed. The surface presented to the wind would be 

 about twelve hundred square feet, and the pressure on each square 

 foot, from our table, would be 1*9 pound, and the total pressure over 

 a ton. A calculation is hardly necessary to show that such a pressure. 



