356 



DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 



thin yielding posterior margins (ef, g h), are allowed to drop from a height (r), 

 they describe double curves in falling, as shown at m n o I, ij k I, the roots of 

 the wings (c, a) reaching the ground first, a circumstance which proves the 

 greater buoying power of the tips of the wings. I might refer to many other 

 experiments made in this direction, but sufficient have been adduced to show 

 that weight, when acting upon wings, or, what is the same thing, upon elastic 

 twisted inclined planes, must be regarded as an independent moving power. But 



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■<r 



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Fig. 23. 



for this circumstance flight would be at once the most awkward and laborious form 

 of locomotion, whereas in reality it is incomparably the easiest and most graceful* 

 The power which rapidly vibrating wings have of sustaining a body which tends 

 to fall vertically downwards, is much greater than one would naturally imagine, 

 from the fact that the body, which is always beginning to fall, is never per- 

 mitted actually to do so. Thus, when it has fallen sufficiently far to assist m 

 elevating the wings, it is at once elevated by the vigorous descent of those 

 organs. The body consequently never acquires the downward momentum 

 which it would do if permitted to fall through a considerable space uninter- 

 ruptedly. It is easy to restrain even a heavy body when beginning to fall, 

 while it is next to impossible to check its progress when it is once fairly 

 launched into space and travelling rapidly in a downward direction (see foot- 

 note to page 371). 



The importance to be attached to weight in flight is variously explained in my Memoir on the 

 subject, Trans. Linn. Society, vol. xxvi. pages 218, 219, 246, 260, and 261. 



