STABILITY 27 



the cardboard being set so as to have an upward 

 incline ; in fact as an aeroplane is set when it is 

 travelling horizontally. This was managed by 

 means of small wire carriers having various inclines, 

 on which the cardboard rested, and which were 

 themselves thrown with the cardboard. So far 

 from pitching head downwards, the cardboard 

 missiles would, even when the angle of deflection 

 from the horizon was small, rise in the air, and some- 

 times even turn over backwards, so strong was the 

 action of the air on the front margin. 



In the bird's wing there is a further automatic 

 safeguard. It curves downwards at the back, 

 at any rate that part of it that is nearer to the body. 

 The wind acting over-strongly upon the downward- 

 curving back part of the wing might, if the whole 

 wing-surface were rigid, capsize the bird and send 

 him diving head-foremost downward. But the 

 elasticity of the feathers prevents an excessive lift. 

 They yield to pressure, and the reduction of their 

 curvature relieves the wing of any excess of pressure 

 on its hinder part. 



The same principle holds good with regard to 

 lateral stability. If a strong gust or eddy of air 

 strikes the right wing while the left is struck with 

 less violence, the feathers of the right wing yield 

 to the rush of air and bend upward, so that the 

 very force of the gust to some extent reduces its 

 effect. Such elasticity would seem to be impossible 

 in the case of an aeroplane without dangerously 

 reducing its strength. And yet an aeroplane, from 

 its enormous breadth, is far more liable than a bird to 

 suffer from gusts falling with unequal force on its 



