122 THE FLIGHT OF BIRDS 



Cormorant style. There was a fresh breeze blowing 

 from the feeding-place to the rock. As a preliminary, 

 therefore, he flew some considerable distance in the 

 opposite direction, then turned and joined the others. 



If the wind is to help the bird to rise he must have 

 inertia ; in other words, he must not drift with it like 

 a balloon, but offer resistance. When he faces the 

 wind and takes his initial jump, obviously he has 

 inertia, for he has just left the earth, which is not 

 moving with the wind. Facing the wind he gets it 

 to help him. Imagine what would happen if he 

 faced in the direction of the wind ; impinging on 

 his back it would drive him downwards to earth 

 again. But the assistance got from the wind does 

 not end with the first jump into the air. The wind 

 rapidly increases in velocity with altitude. During 

 a terrific blizzard I once saw some Gulls with effort 

 making headway against the blast ; they succeeded 

 only by flying so close to the ground that their wings 

 almost touched it. Even when there has been no 

 gale blowing, but only a fairly stiff breeze, I have 

 noticed that Gulls, heading against the wind, will 

 fly as low as possible. Friction reduces the wind's 

 velocity. Some years back some friends and I called 

 in the help of an anemometer in order to get more 

 definite evidence. On one occasion the anemometer 

 recorded a velocity of 770 feet per minute at a 

 height of 2 feet from the ground ; at 7 J feet the 

 velocity rose to 1,000 feet. 



Here are facts of the utmost importance to bird 

 and to aviator. We may for the sake of clearness 

 divide the air into distinct successive streams, the 

 second more rapid than the lowest, and each, as we 



