122 THE FLIGHT OF BIRDS 
Cormorant style. There was a fresh breeze blowing 
from the feeding-plac#to the rock. Asa 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 74 feet the 
velocity rose to 1,000 feet. 
Here are facts of the utmost importance to bie 
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 
