A GIFT OF GOD 23 



full play, too, when the strong fliers are shooting or 

 gliding forward with motionless, outstretched wings. 

 But I think it is not much used by small birds, such 

 as thrushes and finches, once well a-wing and engaged 

 in longer flights; I often see the tail hi these cases 

 doing little or no work. 



The tail is so made that, by its own trifling move- 

 ments, it can work up the air for supporting purpose. 

 But I have wondered whether the tail may not also 

 be fed during flight by some of the air which the 

 wings in their downward and forward strokes churn 

 and leave in agitation. This agitation may not be 

 all used up by the wing, and it must be considerable. 

 Before I knew of Pettigrew's or Marey's theories and 

 tests I wrote of every flying thing, from eagle to 

 the gnat, as riding on a whirlwind of its own making, 

 and I have found since that this is the exact imagery 

 Pettigrew employed. In flights of a few yards, of 

 a yard even, from branch to branch, some birds fan 

 vigorously, tail full spread, and then the air the tail 

 uses may well be that churned by the powerful wing 

 strokes. 



The flight of a quick, strong-winged bird through 

 the air, or of a strong fish through the water, is a 

 good example of the value for purpose of motion 

 that exists in curves. Alike in the bird and the 

 fish, what first appeals to the eye is the arrow straight- 

 ness of line with which they drive through their 

 element. Take a powerful swimmer, the trout, and 



