FLIGHT. 241 



lives on the wing ; it eats, drinks, and collects mate- 

 rials for its nest in flying, and never rests but during 

 darkness. If it be true that birds, when migrating, 

 require a wind that blows against them, it implies an 

 extraordinary power as well as continuance of mus- 

 cular exertion. 



" We see how Nature completes her work, when 

 the intention is that the animal shall rise buoyant 

 and powerful in the air : the whole texture of the 

 frame is altered and made light, in a manner consis- 

 tent with strength. We see also how the mechanism 

 of the anterior extremity is changed, and the muscles 

 of the trunk differently directed *." 



We deemed it the more necessary to enter with 

 some minuteness into the conformation and use of 

 the air-cells, from their not being so obvious to a 

 common observer, in reference to the flying of a bird, 

 as are the wings and the tail, to which we shall now 

 direct attention. 



Though it is obvious that birds could not fly with- 

 out wings, yet the peculiar mechanism of the process 

 is not, we believe, generally understood. It is no 

 uncommon thing to see a goose, while walking on a 

 common, spread out its wings to their full extent, 

 and begin to flap them about with great violence, 

 and yet the bird is not thereby moved an inch from 

 the ground ; a circumstance that, without inquiry 

 into the cause, seems contrary to what might have 

 been anticipated. By observing the difference be- 

 tween this ground-flying (if we may call it so) of the 

 goose, and the actual rising of a pheasant, for ex- 

 ample, into the air, we may arrive at the reason why 

 the goose does not, while the pheasant does, ascend. 

 The goose, it may be remarked, keeps her wings 

 spread both in the upward and the downward 

 motion, and consequently the resistance of the air in 

 * Bridgewater Treatise on the Hand, p, 77. 



