ane FLIGHT aay 
this he would have to be perpetually feeling the 
pulse of the wind, and, moreover, soaring would 
be a much less regular progress upward than it 
is supposed to be. Some turns of the helix would 
be failures. There would be a loss instead 
of a gain of elevation, or nothing more than a 
maintenance of level would be achieved. But when 
we watch a bird circling at a great height, what can 
we tell of his progress during a particular minute? 
We only know that his general tendency is upward. 
Gulls make many only partially successful turns when - 
they soar, and it is possible that similar failures in 
a nobler performer like the Adjutant may remain 
undetected. 
Supposing the irregularity of the wind to be due to 
eddies, the bird may still be able to avail himself of 
it, turning to account the difference in velocity of the 
outer and inner rings of the whirl. This supposes that 
the eddy is of a convenient size. It may be cither so 
large or so small as to be useless to him. The com- 
plications of the problem, when we introduce into it 
the question of eddies, are almost insurmountable. 
In the present state of our knowledge we can only 
say that there are great irregularities of velocity, to 
whatever cause they may be due, and that it is highly 
probable that a bird in soaring turns them to account. 
We are apt to speak of soaring as being effected 
without any muscular effort. But it is by muscles 
that the wings are held fixed and immovable, and the 
strain must be considerable. Apparently, however, 
there is hardly any limit to the time during which a 
bird can continue an exertion of this kind. No such 
