88 FRIENDS WORTH KNOWING. 



Well, how does a bird fly ? It seems simple enough to de- 

 scribe, and yet it is a problem that the wisest in such mat- 

 ters have not yet worked out to everybody's satisfaction* 

 This explanation, by the Duke of Argyle, appears to me to 

 be the best: An open wing forms a hollow on its under- 

 side like an inverted saucer; when the wing is forced 

 down, the upward pressure of the air caught under this 

 concavity lifts the bird up, much as you hoist yourself up 

 between the parallel bars in a gymnasium. But he could 

 never in this waj^ get ahead, and the hardest question is 

 still to be answered. Now, the front edge of the wing, 

 formed of the bones and muscles of the forearm, is rigid 

 and unyielding, while the hinder margin is merely the soft 

 flexible ends of the feathers ; so, when the wing is forced 

 down, the air under it, finding this margin yielding the 

 easier, would rush out here, and, in so doing, would bend 

 up the ends of the quills, pushing them forward out of the 

 way, which, of course, would tend to shove the bird ahead. 

 This process, quickly repeated, results in the phenomenon 

 of flight. 



The vigor and endurance that birds upon the wing dis- 

 play is astonishing. Nearly all the migratory species of 

 Europe must cross the Mediterranean without resting. 

 Many take the direct course between the coast of Africa 



