How A Bird Flies

The most prominent fact about a bird is a f aculty in which it diners from every other oreature except the tïat and insects - its power of flying. JETor this purpose, the bird's arm enda in only one long slender finger, instead of a f uil hand. To this are attached the quüls and email feathers (eoverts) on the upper side, which make up the wing. Observe how light all this is : In the flrst place, the bones are hollow, then the shafta ol the feathers are hollow, and, flnally, the feathers themselves are made of the most delicate filaments, interlocking and clinging to one another with little grasping hooks of microscopio ñneness. Well. how does a bird fly ? It seems simple enoivgh to describe, and yet it is a problem that the wisest in such matters have not yet worked out to everybody's satisfaetion. 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 foreed down the upward pressure of the air caught under this concavity, lifts the bird up, much as you hoist yourself up between the parallel in a gymnasium. But he oould 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 boDes and muscles of the fore-arm, ia rigid and unyieldiug, while the hinder margin is ïnerely the soft flexible ends of the feathers ; so when the wing is fcced down, the air under it, finding this margin yielding the easier would rush out hcre, and, in so doing, would bend up the ends of the quills, pushing them forward out of the way, which, of course, would tend tü shove the bird ahead. This procesa, quickly repeated, results in the phenomenon of flight.- Ernest Ingersoll, in Scribner for September.