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 
