Structure. 21 



servant Bewick bids us note 'the pointed beak, the long and 

 pliant neck, the gently swelling shoulder, the expansive wings, 

 the tapering tail, the light and bony feet, of birds.' Every one of 

 these seem formed to combine, as far as possible, the least weight 

 with the greatest strength. There is no superfluous bulk in the 

 structure of a bird. Compared with its dimensions, and the 

 width of its expanded wings, how trifling and insignificant a 

 proportion does the body seem to occupy ; how every part seems 

 to conduce towards lightness and buoyancy. The plumage, too, 

 with which they are clothed is soft and delicate, and yet so close 

 and thick as to form an admirable protection against the intense 

 cold of the atmosphere through which they wing their way, and 

 to which their swift movements must necessarily expose them ; 

 the feathers which compose it are attached to the skin, somewhat 

 after the manner of hair, and are periodically moulted or changed, 

 and nothing can exceed the beauty, and often brilliancy, of their 

 colouring, as nothing can be conceived more adapted to combine 

 the two objects of extreme warmth and excessive lightness. 

 With such an airy framework, and clothed with a plumage in 

 specific gravity but little exceeding the air itself, we are at no 

 loss to understand the ease with which birds mount from the 

 earth and soar among the clouds ; but to enable them to pass 

 quickly through the air, to progress rapidly and without fatigue, 

 no instruments could be devised more excellent than the wings 

 with which they are provided ; so light and yet so vigorous, fur- 

 nished with such strong muscles, so spacious when extended in 

 flight, and yet so compact when closed in rest. By the help of 

 these oars or sails they can strike the air so forcibly, and with 

 such a succession of rapid and powerful strokes, as to impel for- 

 ward their bodies with wonderful velocity ; the greater the extent 

 of the wings in proportion to the size of the bird, the greater is 

 the facility with which it can sustain itself in the air, and the 

 greater the rapidity of its flight. As an example of this, compare 

 the stretch of wing and the proportionate speed of the common 

 Swift and the common Sparrow. Almost all species can fly with 

 exceeding swiftness ; but the progress of some is so very rapid, as 



