WIND AND FLIGHT 143 
they described their sedate spirals. A bird is cer- 
tainly capable of a great deal during sleep. When 
he sleeps standing on one leg, he is perpetually 
making small adjustments in order to maintain his 
balance. When a Duck sleeps floating on a pond 
with one leg tucked up, he will keep the other 
paddling, so that he may move in a circle and not be 
driven by the wind into the bank, where a hungry 
stoat may be waiting for him. But to sleep while 
soaring is an altogether different matter. The 
soaring bird has not only to make perpetual adjust- 
ments, but also to feel the pulse of the wind, to be 
alive to every gust and find out what adjustments 
have to be made. But the fact that so good an 
observer could hold this theory shows how sedate 
the movement is. Though the pace may vary, there 
is not a rapid sweep down a gentle incline in one-half 
of a circle, then, in the other half, when the bird has 
wheeled round, a slow advance with much gain 
of altitude: nothing corresponding to the gallop of 
the four-in-hand down the last fifty or hundred 
yards of a hill, in order that the coach’s momentum 
may carry it some way up the hill that is immediately 
in prospect. The circling is slow, sedate, and appar- 
ently perfectly comfortable, and sometimes certainly 
the bird keeps rising through a whole turn of the spiral. 
He does not sweep downward in one part, then turn 
and gain elevation. Ii all goes well, if the wind is all 
that is required, there is no loss of altitude from 
beginning to end of the turn; there may be a gain 
throughout. 
The birds that soar are all of considerable size 
Small birds, however expert in flying, are, apparently, 
