78 RAPIDITY OF FLIGHT. 



merits are calculated for, it may be almost said, eternal flight. 

 Its length of wing, ten or twelve feet from tip to tip, forked 

 tail, and short legs (the thighs or tarsi not exceeding an inch 

 in length), bear a close resemblance to those of our common 

 Swift, of whose wonderful powers of flight we have said so 

 much; but nature has provided the Frigate-bird with still 

 more surprising means, for not only floating for a time, but for 

 ever, without fatigue, in the regions of air, and even sleep 

 without risk of falling. We shall endeavour to explain this 

 (at first sight) most improbable capacity, so as to render it no 

 longer a matter of doubt or difficulty, but merely an additional 

 instance of the beautiful arrangement adopted by the providence 

 of God in all His wondrous works. 



On examining it we shall find just beneath the throat a large 

 pouch communicating with the lungs, and with the hollow and 

 particularly light bone-work of its skeleton. Suppose, then, 

 that the bird wishes to rest in the air ; in the first place, it 

 avails itself of its large wings, which it is enabled by constant 

 habit to keep expanded, and which are in themselves nearly 

 sufficient to sustain its weight and float its light body in the 

 air. But in addition to the wing, suppose the bird fills its 

 large pouch with air, and from thence forces it into all its bones 

 and cavities between the flesh and the skin, what will happen ? 

 That the heat of its circulation (and it is well known that the 

 heat of a bird's circulation is considerably beyond that of other 

 animals) will rarefy the internal air, which will therefore puff 

 up not only the pouch, but every cavity, and thus give the bird 

 a surprising additional buoyancy or power of floating even in 

 the higher regions of the atmosphere. And that this is the 

 case may be presumed from its habits; for when the lower 

 currents of air are stormy and disagreeable, up goes the Frigate- 

 bird to a higher and calmer current, where, just as we see the 

 light fleecy clouds in the sky, it remains, suspended with out- 

 spread wing, motionless and at rest, till, roused by hunger, it 

 expels the rarefied air, and emptying its pouch, descends towards 

 the waves ; but as it never either dives or swims, on approach- 

 ing within a few feet it instantly stops and changes its direction, 



