WIND AND FLIGHT 149 
ascending column of air and suddenly find himself 
in a descending one. Captain Brooke-Popham, 
whom I have already quoted, says that it is probable 
that these remous seldom exceed 100 feet in width.* 
In order to understand soaring, which often takes 
place at great heights where it is impossible, at any 
rate for anyone who is not an aviator, to investigate 
air currents, it is well to consider whether it is in 
principle at all different from what we may see taking 
place close at hand where investigation is easy. 
Gulls, as we know, have no difficulty, when the wind 
has an upward trend, in poising upon it and making 
headway against it. We have also seen that, the 
upward trend being there, they will occasionally 
advance, wings motionless, with the wind behind 
or almost behind them. When a soaring Eagle 
wheels round and circles, he does high aloft these 
two things that the Gull does near to the earth. He, 
of course, does something more, for when he makes 
a complete turn of the spiral he must, in the course 
of it, have the wind blowing first on one side of him 
and afterwards on the other. But the Gull too does 
something that approaches to this, for when he 
glides sideways he is not absolutely full face to the 
wind, but makes a slight turn so that it strikes him 
a little on one side. The soaring Eagle faces each 
point of the compass in turn, for he has to circle 
round in order not to pass beyond the limits of the 
upward stream of air that supports him. Let us 
picture him as he turns the spiral. He does not, 
like the earth, keep his axis pointed the same way 
from the beginning to the end of his orbit. As he 
* Loc. ctt., p. 88. 
