. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. a\ the resistance of the air, compared with the re- sistance to the wing when horizontal, is dimi- nished in the ratio of radius to the cube of the sine of inclination, that is, as « b to d c3; con- sequently, a bird with its wings elevated at any angle to the horizontal plane will descend with greater velocity than when they are in the direc- tion of a b. We most frequently observe that Pigeons elevate their wings in this manner until they arrive within a foot or two of the ground, when, to prevent the shock they would
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. a\ the resistance of the air, compared with the re- sistance to the wing when horizontal, is dimi- nished in the ratio of radius to the cube of the sine of inclination, that is, as « b to d c3; con- sequently, a bird with its wings elevated at any angle to the horizontal plane will descend with greater velocity than when they are in the direc- tion of a b. We most frequently observe that Pigeons elevate their wings in this manner until they arrive within a foot or two of the ground, when, to prevent the shock they would otherwise receive, owing to the velocity ac- quired during their descent, they suddenly turn their axis perpendicular, which had previously been parallel, to the direction of their motion, and by a few rapid strokes of the wing neu- tralize their momentum, and thus reach the ground with ease and safety. In order to pro- duce lateral motion one wing oscillates more rapidly than the other, thereby causing the head to turn towards the side to which the latter wing is attached. The tail of the bird performs the office of a rudder in steering its course ; its plane being horizontal tends chiefly, as Borelh has demon- strated, to elevate and depress the head, ratiier than to turn the axis of the bird laterally. Let us, for instance, suppose that a bird, flying in the direction of its axis gf, (fig. 224) elevates Fig. its tail into the position b h parallel to o n, the resistance of the air will depress b towards A, and causing the bird to rotate on its centre of gravity c will elevate the head from a to- wards /; on the other hand, if the tail be de- pressed into the position b i, parallel to I k, by the resistance of the air, the point b will be raised towards n, and the head depressed to- wards o, consequently the direction of the bird in its mesial plane is regulated by the tail.* In the Grallatores the tail is short and its sur- face very small, and the function of a rudd
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