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 



* Log. cit., p. 88. 



