436 DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



with the horizon, depend chiefly upon the speed with which the wing is urged 

 at different stages of the stroke, the angle always decreasing as the speed 

 increases, and vice versa. As a consequence, the angle is greatest when the 

 speed is least. 



The course described, and the angles made by the artificial wave wing with the 

 horizon during the stroke from right to left, are represented at fig. 70, page 435. 



When the wing reaches the point b, its speed is much less than it was at q. 

 The wing is, in fact, preparing to reverse. At c the wing is in the act of revers- 

 ing (compare with c of figs. 16 and 17, page 349), and, as a consequence, its 

 speed is at its minimum, and the angle which it makes with the horizon at its 

 maximum. At d the wing is reversed, its speed being increased, and the angle 

 which it makes with the horizon diminished. Between the letters d and u the 

 wing darts suddenly up like a kite, and at u it is in a position to commence the 

 stroke from left to right, as indicated at u of fig. 71 p. 435. The course described, 

 and the angles made by the wing with the horizon during the stroke from left 

 to right, are represented at fig. 71 (compare with figs. 4 and 6, page 338). The 

 stroke from left to right is in every respect the converse of the stroke from 

 right to left, so that a separate description is unnecessary. 



The Artificial Wave Wing can be driven at any speed — it can make its own 

 currents, or utilise existing ones. — The remarkable feature in the artificial wave 

 wing is its adaptability. It can be driven slowly, or with astonishing rapidity. 

 It has no dead points. It reverses instantly, and in such a manner as to dissi- 

 pate neither time nor power. It alternately seizes and evades the air so as to 

 extract a maximum amount of support with a minimum of slip, and with a 

 minimum expenditure of power. It supplies a degree of buoying and propelling 

 power which is truly remarkable. Its buoying area is nearly equal to half a 

 circle. It can act upon still air, and it can create and utilise its own currents. 

 I proved this in the following manner. I caused the wing to make a horizontal 

 sweep from right to left over a candle ; the wing rose steadily as a kite would, 

 and after a brief interval, the flame of the candle was persistently blown from 

 right to left. I then waited until the flame of the candle assumed its normal 

 perpendicular position, after which I caused the wing to make another and 

 opposite sweep from left to right. The wing again rose kite fashion, and the 

 flame was a second time affected, being blown in this case from left to right. I 

 now caused the wing to vibrate steadily and rapidly above the candle, with this 

 curious result, that the flame did not incline alternately from right to left and 

 from left to right. On the contrary, it was blown steadily away from me, i.e., 

 in the direction of the tip of the wing, thus showing that the artificial currents 

 produced, met and neutralised each other always at mid stroke. I also found 

 that under these circumstances the buoying power of the wing was remarkably 

 increased. 





