62 8 THE POPULAR SCIENCE MONTHLY. 



These circumstances lead to the conviction that the aeronautic 

 problem will most probably admit of a satisfactory solution only 

 by means of dynamic flying machines. Prof. Wellner is of the 

 opinion that, manifold as are the difficulties besetting the road to 

 this end, it is likely to be attained before the close of our century. 

 The inventor's starting point is the observation and analysis of 

 the flight of insects and birds, which have of late been made pos- 

 sible by the graphic methods of chronometric observation and 

 photography. It would, of course, be a mistake to attempt a close 

 imitation of the organs of motion observed in birds or insects, as 

 these would lose their utility through the unavoidable clumsiness 

 of man's appliances. What must be aimed at is the most advan- 

 tageous shape and construction of wings, productive of the 

 greatest propelling poAver with the expenditure of the smallest 

 possible sum of energy ; the application of a light but powerful 

 motor; a contrivance for easy and efficient steering, available 

 alike at the time of the ascent, while flying, and in alighting ; and 

 arrangements for the prevention of accidents. 



It may be regarded as an established fact that gently curved 

 or arched surfaces, pointed toward their ends, make the fittest 

 wings for flying machines ; they must be carried against the 

 atmosphere at small angles. The lifting power of the wings 

 arises from the carrying quality of the air compressed and form- 

 ing, we might say, an air-cushion under the aeroplanes. The air 

 pressure increases in a duplicate ratio to the velocity of the latter ; 

 consequently very small wings are capable of great lifting power 

 when vigorously and swiftly plied. In order to advance the air- 

 ship, a power imparting horizontal motion is needed ; this has to 

 be secured by a retrograde movement, thrusting the air backward 

 and thus causing it to propel the air-ship. The shape, position, 

 and direction of the aeroplanes will have to be such as to com- 

 bine the vertical lifting with the horizontal propulsion. The two 

 great distinct groups of air-ships attempting to secure this end 

 are those propelled by screws and those working on the principle 

 of a kite. 



The models constructed by Ponton d'Amdcourt, Achenbach, 

 Dieuaide, Forlanini, Philipps Popper, Jarolimik, and some others 

 are based on the screw principle. They employ propeller screws 

 moving horizontally on vertical axes and connected with aero- 

 plane surfaces which are capable of inclination between the hori- 

 zontal and vertical positions like those of a windmill. These 

 aeroplanes pressing down the air act very much like the propeller 

 screw in a ship, which drives the water backward so as to make it 

 move the ship forward. The difficulty inherent to this construc- 

 tion arises from a considerable loss of motive power, caused by 

 the difference in revolving speed of the screw at various points 



