278 FACULTIES OF BIRDS. 



strokes upon the air in quick succession; and in 

 descending obliquely, these actions are proportion- 

 ally slower. 



" In birds of prey the form of the wings is very 

 oblique, so that they cannot rise in the air perpen- 

 dicularly unless they fly against the wind; they 

 have, however, a greater power of horizontal mo- 

 tion than other birds, because the extreme parts of 

 the wings are long, and the ends of the feathers lap 

 over each other, which opposes a uniform resist- 

 ance to the air ; while in other birds the air passes 

 through between the feathers, which lessens the 

 power of keeping the wing oblique. To enable 

 themselves to turn to the right or left, they move 

 one wing more rapidly than the other. This is at- 

 tended with difficulty when the flight is rapid ; they 

 therefore make a large sweep before they can turn 

 round."* 



In the ingenious attempts which have been made 

 to devise wings to enable men to fly in the air, it 

 has rarely been taken into account that the muscles 

 of the most powerful arm are proportionably slen- 

 der and weak when compared with the wing-mus- 

 cles of birds; and, therefore, even if wings suffi- 

 ciently efficient could be contrived, the arms would 

 be too feeble to wield them, considering also that 

 there are no aircells distributed through the human 

 body as in birds, to diminish its specific gravity by 

 inflation. 



* Home, Comp. Anat., i., 8. 



