210 



TIGREW ON THE MECHANISM OF FLIGHT 



Flight of the Flying fish $ 



Whether the Plyingfish uses its greatly expanded pec 



toral fins as 8 bird its wings, or only as parachutes, has not, so far as I am aware, 

 been determined by actual observation. Most observers are of opinion that these 



creatures glide up the wind and do not beat it after the manner of birds 



of a circle, the sea 



sup 



so that their flight (or, rather, leap) is indicated by the arc 

 plying the chord. I have carefully examined the structure, relations, and action of 

 those fins, and am satisfied in my own mind that they act as true pinions within 

 certain limits, their inadequate dimensions only preventing them from sustaining the 

 fish in the air for an indefinite period — at all events so long as they remain moist. 

 When the fins are fully flexed, as happens when the fish is swimming, they are arranged 



are raised above the 



the sides of the body ; but when it takes to the 



they 



body and make a certain angle with it. In being raised they are likewise turned 

 outwards, the fin rotating on its axis until it makes an angle of something like 30° with 

 the horizon — this beins*. as nearly as I can determine, the greatest angle made by the 



or down stroke in the flight of insects and birds*. The angle 



o 



g during the effective 



o 



which the wing makes with the long axis of the body, from the fact of the trunk bein 

 usually inclined obliquely upwards in flight, is considerably less than 30°, and probably 

 does not exceed 15° or 20°. It varies, however, during the flexion and extension of the 

 Wing, and also, though in a less degree, during the down and up strokes — the angle being 

 gradually increased when the wing descends, and 

 ascends. 



pondingly decreased when it 



It is further determined by the absence or presence of atmosphei 



ents 



by the shape and size of the body, the expanse of 

 shown in the annexed woodcuts 



o 



and the rapidity of flight 



Horizon 



Horizon 



Diagram 3. 



Duck in ordinary flight. 



Diagram 4. — Duck in rapid flight. 



The angle assigned must therefore be regarded as only approximately true. The increase 

 or diminution of the angle made by the wing and by the body with the horizon in flight 

 enables the insect and bird to balance themselves with remarkable adroitness, and to main- 



alter their position at pi 



This balancing-power is well seen in the I lummin 



bird, Humming-bird Moth f, and -Wind-hover (PI. XV. fig. CO), all of winch can, by the 

 rapid oscillation of their wings, and by the judicious management of the angle at which they 



* In a lecture which I delivered at the Royal Institution of Great Britain "On the Various Modes of Flight in 

 Relation to Aeronautics," I stated the angle at which the wing strikes the air during the downward stroke to be 45°. 

 Recent examinations, however, induce me to believe that the one given above is relatively the more accurate. 



(Mt 



March 1867.) 



appearance 



beak . 



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