PETTIGREW ON THE MECHANISM OF FLIGHT. 211 



cause them to strike, fix themselves, as it were, in the air*. It is also observable in i lie 

 gyrations of the Eagle and Albatros (see Diagram), both of which modify the angle in 

 such a manner as enables them to sail about for incredible periods, and to lly immeiiae 

 distances without apparently moving the wings at all. The wing, it nppean to me, is 

 applied to the air very much after the manner of a boy's kite — the angle in the kite being 

 modified and determined by the stiffness of the breeze, and the length and weight of the 



string and tail. The pectoral fin of the Elyingfish affords a <»od illustration of its 



peculiar mode of action. In this anomalous and interesting creature I he il ving-iin or w ing 

 attacks the air from beneath, whilst it is being raised above the bodyf. Ji has no down- 

 ward stroke, the position and attachments of the fin prevent inn 1 it from descending beneath 

 the level of the body of the fish. In this respect the llying-lin of the lish materially 

 differs from the wing of the insect, bat, and bird. The gradual expansion and raising of 

 the fins of the fish in almost the same plane during extension accounts for the admitted 

 absence of beating, and has no doubt originated the belief that the pectoral fins arc merely 

 passive organs. If, however, they do not act as true pinions within the limits prescribed, 

 it is difficult, and, indeed, impossible, to understand how such small creatures could obtain 

 the momentum necessary to project them a distance of 200 or more yards, and to attain, 

 as they sometimes do, an elevation of 20 or more feet above the water. Mr. Swainson, 

 in crossing the line in 1816, zealously attempted to discover the true action of the fins 

 in question; but the flight of the fish is so rapid that he utterly failed, lie gives it as 

 his opinion that flight is performed in two ways,— 1st by a spring or leap, and 2nd by tin 

 spreading of the pectoral fins, which are employed in propelling the fish in a forward 

 direction, either by flapping or by a motion analogous to the skimming of Swallows. lie 

 records the important fact that the Elyingfish can change its course after leaving the 

 water, which satisfactorily proves that the fins are not limply passive structures. 3»£r. 

 Lord, of the Royal Artillery J, thus writes of those remarkable specimens of the finny tribe. 

 "There is no sight more charming or pleasant to remember than the flight of a shoal 

 of Elyingfish as they shoot forth from the dark-green wave in a glittering throng, like silver 

 birds in s°ome gay fairy tale, gleaming brightly in the sunshine, and t hen, with a mere touch 

 on the crest of the heaving billow, again flitting onward reinv i gorated and refreshed." 



This circumstance goes against the belief that the wing requires to operate upon fresh or undisturbed columns of air 



at each stroke to prove effective. Indeed the rapid division and reunion of the air renders this condition in a measure 

 unnecessary. For explanation of the manner in which the wing acts in these cases ride itfri. Although the insect 

 and bird can sustain themselves in the air by acting upon air previously agitated, I think it proper to observe that, m such 



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instances, the muscular efforts required are incomparably greater than when fresh columns are operated upon, and when 

 insect and bird are progressing at a high speed. Tn the latter case the momentum acquired by the body reduces the 

 excessive expenditure of muscular action, the velocity attained securing additional support^ not giving the par- 

 ticles of air acted upon time to escape or separate 



t In insects whose wing* during the period of repose are raised vertically above their backs, as is the case m Butter, 

 flies, the wings are lowered and slewed round till they make an angle of 30°, or thereabouts, with the horizon, so 



The Butterfly, as well as insects generally, has there- 



fo7e\^ovvr a n7airup"stroke-the Flyingfish having only the latter. In the insect the stroke is delivered, as it 

 were, at the proper angle, and the gliding upward follows, but so closely as to be almost simultaneous; whereas in the 

 Flyingfish the stroke and the gliding upward* are synchronous 

 t * Nature and Art,' November I860, p. 1 73. 



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