WILD LIFE OF ORCHARD AND FIELD 



describe, and yet it is a problem that the wisest 

 in such matters have not yet worked out to every- 

 body's satisfaction. This explanation, by the 

 Duke of Argyle, appears to me among the best: 

 An open wing forms a hollow on its underside 

 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 gym- 

 nasium. But he could never in this way 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 fore-arm, 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 phe- 

 nomenon of flight. 



The vigor and endurance that birds upon the 

 wing display is astonishing. Nearly all the 

 migratory species of Europe must cross the Medi- 

 terranean without resting. Many take the direct 



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