Flying Machines. 377 



vane communicates its own motion to the air, the reaction of 

 the air against the motion of the vane will be lessened. If at 

 each moment of its progress in a horizontal direction the vane 

 acted npon a stratum of air whose vis inertice had not been 

 disturbed, the maximum of reaction would be obtained. Mr. 

 Wenham, in a very ingenious way, applies these facts to the 

 action of the long wings of swallows, and other birds charac- 

 terized by the length of their . flying apparatus, and he shows 

 very pointedly the great mechanical disadvantage at which a 

 bird or a machine must operate in order to raise a weight per- 

 pendicularly, as compared with raising it obliquely. He says 

 it does not appear that any large bird can raise itself perpen- 

 dicularly in a still atmosphere, but pigeons can accomplish it 

 approximately to a moderate height, and the humming-bird, by 

 the extremely rapid vibration of its pinions, can sustain itself 

 for one minute in still air in the same position. ' ( The muscular 

 force required for this feat being much greater than for any 

 other performance of flight. The wings uphold the weight, 

 not by striking vertically downwards upon the air, but as in- 

 clined surfaces reciprocating horizontally like a screw, but 

 wanting in its continuous rotation in one direction/ - ' and, there- 

 fore, with some loss of power from the rapid alternation of 

 motion. 



A bird is sustained in the air by the weight of that fluid, and 

 the sustaining power of its wings will depend upon the quan- 

 tity or weight of air that would have to be displaced by its 

 fall. By a wide stretch of wing, and a horizonal motion, the 

 resistance is maximized, and a long-winged bird that has raised 

 itself in the air may avoid falling by maintaining a certain 

 horizontal velocity with a moderate expenditure of force. 



A kite is sustained and moved obliquely by the force of the 

 wind, and the weight of the air which its fall must displace. 

 Thus there is some analogy between a wing and a kite, it being 

 mechanically pretty much the same thing, whether a breeze 

 blows against a resisting surface, or a resisting surface is moved 

 against a mass of air. Mr. Wenham cites an experiment of 

 Captain Dansey, in which a kite, having a surface of only 55 

 square feet, raised a weight of 92Jlbs. in a strong breeze, and 

 he considers that exploring kites might be safer and more con- 

 venient than exploring balloons for purposes* of war, though 

 their employment would be dependent on the force of the wind. 



Notwithstanding the ingenuity of the preceding explana- 

 tions, the reader may scarcely be prepared to admit Mr. 

 Wenham' s inference, that "man is endowed with sufficient 

 muscular power to enable him to take individual and extended 

 flights, and that success is probably only involved in a question 

 of suitable mechanical adaptations." An imitation of the 



