38 HOLDING ON IN AIR. 



taken above or in front. The wings are always more 

 or less hollow on the under sides, and they take hold 

 of the air by millions of fibres ; so that a bird with 

 its flying feathers on the stretch, would fall much 

 more slowly than one would suppose from the differ- 

 ence between its specific gravity and that of the air. 



The resistance which all the feathers on the body 

 of the bird offer to motion backwards is still greater ; 

 and it increases with the force which tends to move 

 the animal in that direction. The instant that it 

 begins to be driven backwards so that a current 

 against its body is produced, the points of the feathers 

 rise, ana take the wind with so many fibres that the 

 resistance is very similar to that made by a scaly 

 fish, when one attempts to draw one of these by the 

 tail; and every one who has angled, and accidentally 

 caught even a common trout in that way, knows that 

 an ounce weight is as difficult to land when so hooked 

 as a pound weight is when hooked by the head. 

 But the feathers of birds rise much more in propor- 

 tion than the free edges of the scales upon any fish ; 

 and they are every way as well formed for " holding 

 on" in the air, as those are for holding on in the 

 water. Thus the bird may be said to resist motion 

 backwards in the air, by throwing out the point of 

 each feather like the " fluke " of an anchor. 



And all this curious complexity of structure is 

 necessary for enabling the bird to perform those 

 motions which, in the case of an "air-bird," or one 

 which is much on the wing, and on it in all weathers, 

 is absolutely necessary. We are so much in the habit 

 of seeing birds fly, and they fly with such apparent 

 ease, that we are apt to overlook the many mechanical 

 difficulties that have to be overcome by their organi- 

 sation. But when attempts have been made by men 



