THE MASTERY OF THE AIR 245 
fect them—no one knows; but they have the 
same general nature as scales, and perhaps 
they may be thought of as glorified scales or 
parts of scales. 
DIFFERENT KINDS OF FLYING IN BIRDS 
In the ordinary flight of a bird the wings 
begin vertically above the back, and every one 
is familiar with the “clap” that they make in 
pigeons when they strike one another. They are 
drawn forwards, downwards, and backwards 
by the muscles which depress the wing, the 
largest of which, for it has most work to do, 
sometimes weighs half the whole weight of the 
bird. At the end of the downstroke the wing 
is pulled up again to begin another stroke. 
To describe a complete movement four ad- 
verbs are required—forwards, downwards, 
backwards, upwards; and the tip of the wing 
moves through a complex curve, like a figure 
8 of which the upper part is much the larger. 
A bird is lightly built, but every bird is 
heavy, and if it be killed it falls to the ground 
with a thud. As Ruskin said, we go quite 
wrong if we think of a bird as like a buoyant 
balloon; it is like a flying bullet. In other 
