ON AF.RIAL LOCOMOTION, 313 



ble degree of "slii)" and direct Ibrward resi«taiice. Tlionsauds of ex- 

 amples in nature testify its success and sliow tlie principle in perfec- 

 tion, — apparently the only one, and therefore beyond the reach of 

 amendment, — the wing of a bird, combining a propelling and supporting- 

 organ in one, each perfectly efficient in its mechanical action. 



This leads to the consideration of the amount of power reqnisite to 

 maintain the tlightof a bird. Anatomists state that the pectoral mus- 

 cles for giving motion to the wings are excessively large and strong; 

 but this furnishes no proof of the expenditure of a great amount of force 

 in the act of Hying. The wings are hinged to the body like two powerful 

 levers, and some counteracting force of a passive nature, acting like a 

 spring under tension, must be requisite merely to balance tlie weight of 

 the bird. It can not be shown, that while there is no active motion, 

 there is any real exertion of muscular force, for instance, during the 

 time when a bird is soaring with motionless wings. This must be con- 

 sidered as a state of eciuilibvium, the downward spring and elasticity 

 of the wings vserving to support the body, the muscles in such a case 

 ])erformiug like stretched india-rubber spring would do. The motion 

 or active power required for the performanceof flight must be considered 

 exclusive of this. 



It is difticult, if not impossible, by any form of dynamometer to ascer- 

 tain the precise amount of force given out bj' the wings of birds; but 

 this is perhaps not requisite in proof of the principle involved ; for when 

 the laws governing their movements in air are better understood it is 

 quite possible to demonstrate by isolated experiments the amount of 

 power required to sustain and propel a given weight and surface at any 

 speed. 



If the pelican, referred to as weighing 21 pounds with near the same 

 atnount of wing area (in square ieet), were to descend perpendicularly, 

 it would fall at the rat'e of 1,320 feet per miiuite (22 feet per second), 

 being limited to this speed by the resistance of the atmosphere. 



The standard generally employed in estimating power is by the rate 

 of descent of a weight. Therefore, the weight of the bird being 21 

 j)Ound«!, which falling at the above speed, will expend a force on the air 

 set in motion nearly equal to 1 horse (.84 horse-power) or that of five men ; 

 and conversely, to raise this weight again perpendicularly upon a yield- 

 ing support like air, would require even more power than this expres- 

 sion, which it is certain that a pelican does not possess ; nor does it 

 appear that any large bird has the faculty of raising itself on the wing 

 ])erpendicularly in a still atmosphere. A pigeon is able to accomplish 

 this nearly, mounting to the top of a house in a very narrow compass ; 

 but the exertion is evidently severe and can only be maintained for a 

 short period. For its size, this bird has great jmwer of wing ; but this 

 is perhaps far exceeded in the humming-bird, which, by the extremely 

 rapid movements of its pinions, sustains itself for more than a minute 

 in still air in one position. The muscular force required for this feat is 



