FLIGHT. 243 



with the fingers closed, slanting, in a similar way to 

 the bird raising its folded wings, so as to diminish 

 the surface opposed to the resisting medium *. The 

 direction in which a bird can fly depends greatly on 

 the form of its wings ; and hence Sir Everard Home 

 justly infers, that a motion directly upwards can 

 only be performed by birds whose wings are nearly 

 horizontal, as the lark and the quail. " In general,'' 

 he says, " the wings are placed oblique : this is prin- 

 cipally owing to the length of their feathers, the fixed 

 point of which is at the root. When birds fly hori- 

 zontally, their motion is not in a straight line, but 

 obliquely upwards, and they allow the body to come 

 down to a lower level before a second stroke is made 

 by the wings, so that they move in a succession of 

 curves. To ascend obliquely, the wings must re- 

 peat their strokes upon the air in quick succession ; 

 and in descending obliquely, these actions are pro- 

 portionally 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 motion 

 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 resistance 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 attended with diffi- 

 culty when the flight is rapid ; they therefore make a 

 large sweep before they can turn round f." 



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 

 * J. R. f Home, Comp. Anat. i. 109. 



