DE, PETTIGKEW ON THE PHYSIOLOGY OF WINGS. 



353 



and wing when oscillating on either side of the fixed point x, this furnishing 

 the fulcrum on which the body and the wing alternately act. The pecu- 

 liarity, however, of the wing consists in the fact that it is a flexible lever and 



Fig. 21. 



^~ I 



Fig. 22. 



acts upon yielding fulcra (the air), the body participating in, and to a certain 

 extent perpetuating the movements originally produced by the pinion. The 

 part which the body performs in flight is illustrated at fig. 21. At a the body 

 is depressed, the wing being elevated and ready to make the down stroke at b. 

 The wing descends in the direction c d, but the moment it begins to descend 

 the body moves upwards and forwards (see arrows) in a curved line to e. As 

 the wing is attached to the body it is made gradually to assume the position/. 

 The body is now elevated and the wing depressed, the under surface of the 

 latter being so adjusted that it strikes upwards and forwards as a kite would. 

 The body now falls doivmvards and forwards in a curved line to g, and in doing 

 this it elevates or assists in elevating the wing to /. The pinion is a second 

 time depressed in the direction k I, which has the effect of forcing the body 

 along a waved track and in an upward direction until it reaches the point 

 m. The ascent of the body necessitates the descent of the wing as at n. The 

 body and wing, as will be seen from this figure, are alternately above and beneath 

 a given line x x. The same points are shown at fig. 22, the only difference 

 being that the sweep of the wing is greater and the undulation made by the 

 body less abrupt, as seen in vigorous flight. At a the body is depressed/and 

 the wing (b) elevated high above the body. The pinion (b) descends in the 

 direction c d, and forces the body in an upward curve to e. The body (e) is 

 now elevated and the wing (/) depressed. The body (<?) falls doivmvards and 



wings, which, was the more necessary, as the surface from which they rose was in many cases a yield- 

 ing surface. The falling forward of the body during flight was indicated in my Memoir " On the 

 Mechanism of Flight," Trans. Linn. Society, vol. xxvi. p. 22G. 



