238 



AERONAUTICS. 



clearly shows that the down and up strokes are parts of one 

 whole, and that neither is perfect without the other. 



The wave wing is endowed with the very remarkable pro- 

 perty that it will fly in any direction, demonstrating more or 

 less clearly that flight is essentially a progressive movement, 

 i.e. a horizontal rather than a vertical movement. Thus, if 

 the anterior or thick margin of the wing be directed up- 

 wards, so that the under surface of the wing makes a fonvard 

 angle with the horizon of 45°, the wing will, when made to 

 vibrate by the hand, fly with an undulating motion in an 

 upward direction, like a pigeon to its dovecot. If the under 

 surface of the wing makes no angle, or a very small forward 

 angle, with the horizon, it will dart forward in a series of 

 curves in a horizontal direction^ like a crow in rapid horizontal 

 flight. If the anterior or thick margin of the wing be directed 

 downwards, so that the under surface of the wing makes a 

 backward angle of 45° with the horizon, the wing will de- 

 scribe a waved track, and fly downwards, as a sparrow from 

 a house-top or from a tree (p. 230). In all those move- 

 ments progression is a necessity. The movements are 

 continuous gliding forward movements. There is no halt or 

 pause between the strokes, and if the angle which the under 

 surface of the wing makes with the horizon be properly 

 regulated, the amount of steady tractile and buoying power 

 developed is truly astonishing. This form of wing, which 

 may be regarded as the realization of the figure-of-8 theory 

 of flight, elevates and propels both during the down and up 

 strokes, and its working is accompanied with almost no slip. 

 It seems literally to float upon the air. No wing that is 

 rigid in the anterior margin can twist and untwist during its 

 action, and produce the figure-of-8 curves generated by the 

 living wing. To produce the curves in (][uestion, the w^ng 

 must be flexible, elastic, and capable of change of form in all 

 its parts. The curves made by the artificial wing, as has 

 been stated, are largest when the vibration is slow, and least 

 when it is quick. In like manner, the air is thrown into 

 large waves by the slow movement of a large wing, and into 

 small waves by the rapid movement of a smaller wing. The 

 size of the wing curves and air waves bear a fixed relation to 

 each othor, and both are dependent on the rapidity with 



