THE MASTERY OF THE AIR 245 



feet 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. 



V 



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 



