PROGKE&SiON IN OK THKOUGH THE AIR. 113 



kn example of flight produced by purely mechanical appli- 

 ances. The winged seeds fly in precisely the same manner. 

 The seeds of the plane-tree have, e,g, two wings which 

 exactly resemble the wings employed for flying ; thus they 

 taper from the root towards the tip, and from the ante- 

 rior margin towards the posterior margin, the margins being 

 twisted and disposed in different planes to form true screws. 

 This arrangement prevents the seed from falling rapidly or 

 vertically, and if a breeze is blowing it is wafted to a con- 

 siderable distance before it reaches the ground. Nature is 

 uniform and consistent throughout. She employs the same 

 principle, and very nearly the same means, for flying a heavy, 

 solid seed which she employs for flying an insect, a bat, or a 

 bird. 



When artificial wings constructed on the plan of natural 

 ones, with stift* roots, tapering semi-rigid anterior margins, 

 and thin yielding posterior margins, are allowed to drop from 

 a height, they describe double curves in falling, the roots of 

 the wings reaching the ground first. This circumstance 

 proves the greater buoying power of the tips of the wings as 

 compared with the roots. I might refer to many other 

 experiments made in this direction, but these are sufficient to 

 show that weight, when acting upon wings, or, what is the 

 same thing, upon elastic twisted inclined planes, must be re- 

 garded as an independent moving power. But for this cir- 

 cumstance flight would be at once the most awkward and 

 laborious form of locomotion, whereas in reality it is incom- 

 parably the easiest and most graceful. The power which 

 rapidly vibrating wings have in 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 permitted actually to do 

 so. Thus, when it has fallen sufficiently far to assist in 

 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 per- 

 mitted to fall through a considerable space uninterruptedly. 

 It is easy to restrain even a heavy body when beginning to 

 fall, while it is next to impossible to check its progress when 



