PKOGKESSION IN OR THEOUGH THE AIR. 



201 



albatross, the ceaseless activity of those of the humming-bird 

 may be adduced. In those delicate and exquisitely beautiful 

 birds, the wings, according to Mr. Gould, move so rapidly 

 when the bird is poised before an object, that it is impossible 

 for the eye to follow each stroke, and a hazy circle of indis- 

 tinctness on each side of the bird is all that is perceptible. 

 When the humming-bird flies in a horizontal direction, it 

 occasionally proceeds with such velocity as altogether to elude 

 observation. 



The regular and irregular in Flight. — The coot, diver, duck, 

 and goose fly with great regularity in nearly a straight line, 

 and with immense speed ; they rarely if ever skim or glide, 

 their wings being too small for this purpose. The wood- 

 pecker, magpie, fieldfare and sparrow, supply examples of 

 what may be termed the " irregular " in flight. These, as is 

 well known, fly in curves of greater or less magnitude, 

 by giving a few vigorous strokes and then desisting, the 

 eff*ect of which is to project them along a series of para- 

 bolic curves. The snipe and woodcock are irregulS^r in 

 another respect, their flight being sudden, jerky, and from 

 side to side. 



Mode of ascending, descending, turning, etc, — All birds which 

 do not, like the swallow and humming-birds, drop from a 

 height, raise themselves at first by a vigorous leap, in which 

 they incline their bodies in an upward direction, the height 

 thus attained enabling them to extend and depress their 

 wings without injury to the feathers. By a few sweeping 

 strokes delivered downwards and forwards, in which the 

 wings are made nearly to meet above and below the body, 

 they lever themselves upwards and forwards, and in a sur- 

 prisingly short time acquire that degree of momentum which 

 greatly assists them in their future career. In rising from 

 the ground, as may readily be seen in the crow, pigeon, 

 and kingfisher (fig. 102, p. 183), the tail is expanded and the 

 neck stretched out, so that the body is converted into an 

 inclined plane, and acts mechanically as a kite. The centre 

 o^ gravity and the position of the body are changed at the 

 will of the bird by movements in the neck, feet, and tail, 

 and by increasing or decreasing the angles which the under 

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