28 THE FLIGHT OF BIRDS 



two extremities. At present the aviator is at a 

 great disadvantage as compared with a bird. The 

 great expanse of his planes is in itself a danger, 

 and his machine has less power of automatic adjust- 

 ment. Moreover, the most experienced pilot is 

 a mere novice compared with a bird that has flown 

 many times every day since he left the nest. Still, 

 birds as flyers have already reached their zenith; 

 for aviators greater things are still possible. 



Leaving the possibilities or impossibilities of the 

 future, I must return to the bird as he is, and call 

 attention to another point which promotes stability. 

 The extremities of the wings of the best flyers 

 have very little downward curve. If they are 

 travelling very fast through the air, the primary 

 wing-feathers may even bend slightly upwards, 

 and aviators have found that the upward incline 

 of their " planes " reduces the amount of rolling. 

 Thus inclined they give less support than if curved 

 downwards at the extremities, but the very fact 

 that the air is allowed to escape easily to right and 

 left is favourable to equilibrium. If an attempt 

 is made by bending the extremities downward to 

 check its escape, to coop it up, it may make a 

 sudden rush from the right or from the left con- 

 cavity and cause risk of a capsize. The wing, 

 amply concave as it is till it begins to taper, and 

 shallowing as it tapers, keeps in view the questions 

 of lift and equilibrium ; it holds the air, yet provides 

 for its escape. Sometimes when a bird wishes to 

 glide downward he will point his wings steeply 

 upward — a method often adopted by pigeons — 

 much more steeply than the right and left surfaces 



