WELLNER'S SAIL -WHEEL FLYING MACHINE. 629 



nearer to or remoter from the axis. This diiference of speed in 

 the turning of the screw combined with the inevitably small 

 angles at which its slanting surfaces are presented to the wind 

 make it incapable of developing, by the help of any of the dynamo 

 machines now in use, a power adequate to the weight of the 

 machine itself, its accessories, and the aeronauts. 



The laws that come into play in the flying of a kite are in- 

 volved in the flight of birds independent of the movement of their 

 wings. In calm weather the kite is moved forward by the boy, 

 who runs along, drawing the string with him. This movement, 

 creating a wind under the kite, causes the air to gather under its 

 slanting surface, and thus calls into play the lifting power of the 

 atmosphere. The flying machines propelled from the rear by a 

 motor with sufficient velocity, on rising into the air are enabled 

 to soar on the same principle. The stronger the wind, the better 

 the kite will rise ; the quicker the horizontal motion of the flying 

 machine, the better its aeroplanes will develop the supporting 



Fio. 2. Lilientiial's Flying Apparatus. The start. 



power of the air. The exertion made by a bird on traveling a 

 long distance is smaller, and its sailing jjower greater, the faster 

 it flies. 



The fastest fliers have the smallest wing surface. Some birds 

 even reduce the area of their supporting surfaces when they in- 

 crease their speed by drawing in their wings and closing their 

 tails. Consequently, in order to keep the aeroplanes of the flying 

 machine within a moderate size, considerable velocity has to be 

 developed. This at the same time serves to overcome the resist- 

 ance of the wind and of air currents. The air-ship is not capable 

 of maintaining the direction pursued unless its velocity is so 

 much greater than that of the strongest wind that it can over- 

 come the latter and yet have velocity to spare. 



While the construction of the kite machines seems to insure 

 success through the high velocity of movement that must be 

 attained, a new obstacle arises from the difficulty of ascent. The 

 speed of motion being the condition of their rising power, they 



