Wing covert

“ The Wing at all times thoroughly under control.—The wing is moveable in all parts, and can be wielded intelligently even to its extremity; a circumstance which enables the insect, bat, and bird to rise upon the air and tread it as a master—to subjugate it in fact. The wing, no doubt, abstracts an upward and onward recoil from the air, but in doing this it exercises a selective and controlling power; it seizes one current, evades another, and creates a third; it feels and paws the air as a quadruped would feel and paw a treacherous yielding surface. ”

“ Above all, an untiring and swift wing is necessary, one that does not flag in the pursuit of game desperately putting forth its utmost efforts to escape, and one that is not baffled by the tortuous course of a moth driven to bay. A beak inordinately cleft and wings of extraordinary power—such, in a word, should be the equipment of the bird whose hunting ground is the vast expanse of the open air. ”

“ The wave wing is endowed with the very remarkable property that it will fly in any direction, demonstrating more or less clearly that flight is essentially a progressive movement, i.e. a horizontal rather than a vertical movement. Thus, if the anterior or thick margin of the wing be directed upwards, so that the under surface of the wing makes a forward angle with the horizon of 45°, the wing will, when made to vibrate by the hand, fly with an undulating motion in an upward direction, like a pigeon to its dovecot. ”

“ They afford an opportunity only of admiring at a distance the extraordinary agility and the stateliness likewise of their motions, the richness of their plumage, and the great propriety there was of ascribing to them ‘an expanded, quivering wing.’ Nothing certainly can be more beautiful and entertaining than such a sight! the wings, by their repeated though unwearied vibrations, equally serving them for sails and oars; while their feet, no less assisting in conveying them out of sight, are no less insensible of fatigue. ”

“ The wing is beautifully twisted upon itself, and when it is elevated and advanced, it rolls up from the side of the bird at varying degrees of obliquity, till it makes a right angle with the body, when it presents a narrow or cutting edge to the water. The wing when fully extended, as in ordinary flight, makes, on the contrary, an angle of something like 30° with the horizon. When the wing is depressed and carried backwards,58 the angles which its under surface make with the surface of the water are gradually increased. ”

“ It is necessary that the wings descend further than they ascend; that the wings be convex on their upper surfaces, and concave on their under ones; and that the concave or biting surfaces be brought more violently in contact with the air during the down stroke than the convex ones during the up stroke. The greater range of the wing below than above the body, and of the posterior margin below than above a given line, may be readily made out by watching the flight of the larger birds. It is well seen in the upward flight of the lark. ”

“ An artificial wing, propelled and regulated by the forces recommended, is in some respects as completely under control as the wing of the insect, bat, or bird.
Necessity for supplying the Root of Artificial Wings with Elastic Structures in imitation of the Muscles and Elastic Ligaments of Flying Animals.—Borelli, Durckheim, and Marey, who advocate the perpendicular vibration of the wing, make no allowance, so far as I am aware, for the wing leaping forward in curves during the down and up strokes. ”

“ Flexion of the Wing necessary to the Flight of Birds.—Considerable diversity of opinion exists as to whether birds do or do not flex their wings in flight. The discrepancy is owing to the great difficulty experienced in analysing animal movements, particularly when, as in the case of the wings, they are consecutive and rapid. My own opinion is, that the wings are flexed in flight, but that all wings are not flexed to the same extent, and that what holds true of one wing does not necessarily hold true of another. ”

“ The curves and the reversal thereof are necessary to give continuity of motion to the wing during its vibrations, and what is not less important, to enable the wing alternately to seize and dismiss the air.
70 In birds which skim, sail, or glide, the pinion is greatly elongated or ribbon-shaped, and the weight of the body is made to operate upon the inclined planes formed by the wings, in such a manner that the bird when it has once got fairly under weigh, is in a measure self-supporting. ”

“ That birds which fly with flapping wings derive their support from the air, is undoubtedly true, and that the lift produced is due, not to the form, or shape, or area of the wing, is also beyond question. The records show that every conceivable type of outlined structure is used by nature; the material and texture of the wings themselves differ to such a degree that there is absolutely no similarity; some have concaved under surfaces, and others have not; some fly with rapidly beating wings, and others with slow and measured movements ”

“ The Wing, when advancing with the Body, describes a Looped and Waved Track.—Although the figure-of-8 represents with considerable fidelity the twisting of the wing upon its long axis during extension and flexion, and during the down and up strokes when the volant animal is playing its wings before an object, or still better, when it is artificially fixed, it is otherwise when it is free and progressing rapidly. ”

“ The wing would have much less purchase on fig. 8 than on fig. 9, provided the surfaces exposed by the latter were passive or dead surfaces. But they are not dead surfaces: they represent the spaces occupied by the rapidly vibrating wings, which are actively moving flying organs. As, moreover, the wings travel at a much higher speed than any wind that blows, they are superior to and control the wind; they enable the insect to dart through the wind in whatever direction it pleases. ”

“ The flexion of the wing is most obvious when the bird is exerting itself, and may be detected in birds which skim or glide when they are rising, or when they are vigorously flapping their wings to secure the impetus necessary to the gliding movement. ”

“ How to apply Artificial Wings to the Air.—Borelli, Durckheim, Marey, and all the writers with whom I am acquainted, assert that the wing should be made to vibrate vertically. I believe that if the wing be in one piece it should be made to vibrate obliquely and more or less horizontally. ”

“ The way in which the natural wing rises and falls on the air, and reciprocates with the body of the flying creature, has a very obvious bearing upon artificial flight. In natural flight the body of the flying creature falls slightly forward in a curve when the wing ascends, and is slightly elevated in a curve when the wing descends. The wing and body are consequently always playing at cross purposes, the wing rising when the body is falling and vice versa. ”

“ A wing constructed on this principle gives a continuous elevating and propelling power. It develops figure-of-8 curves during its action in longitudinal, transverse, and oblique directions. It literally floats upon the air. It has no dead points—is vibrated with amazingly little power, and has apparently no slip. It can fly in an upward, downward, or horizontal direction by merely altering its angle of inclination to the horizon. It is applied to the air by an irregular motion—the movement being most sudden and vigorous always at the beginning of the down stroke.—Original. ”

“ The plane of the wing at its base varies but little during flight; the plane of the median part of the wing is very much displaced on one and the other side of its mean position; finally, the outer part of the wing, and especially its tip, experiences considerable change of plane. This warping of the wing is modified at each instant during its elevation and depression, in the manner just indicated; at the extreme points of its beat the wing is nearly plane. ”

“ To meet this difficulty, the wing is so shaped that it is concave or hollow upon its lower surface, so that it gathers the air together and prevents it from escaping; while the upper surface is convex or bulging, so that the air slides off from it when the wing is moved upward. ”

“ In all the wings which I have examined, whether in the insect, bat, or bird, the wing is recovered, flexed, or drawn towards the body by the action of elastic ligaments, these structures, by their mere contraction, causing the wing, when fully extended and presenting its maximum of surface, to resume its position of rest and plane of least resistance. ”

“ The upper surface of the wing is convex, the lower surface concave. In flying the wings are thrown forward and downward. Flying is not a flapping of the wings up and down, and if a bird were to strike its wings backward and downward, as its manner of flight is so often pictured, it would turn a forward somersault in the air. ”

“ Their plumage is of the finest order, copious, and without the slightest stain. They find great difficulty in getting on wing, and must run twenty or thirty yards along the ground with expanded wings, before they can get fairly under way. ”

“ Hence the whole mass of the bird rebounds, making a fresh leap through the air; whence it follows that flight is simply a motion composed of successive leaps accomplished through the air. And I remark that a wing can easily beat the air in a direction almost perpendicular to its plane surface, although only a single one of the corners of the humerus bone is attached to the scapula, the whole extent of its base remaining free and loose, while the greater transverse feathers are joined to the lateral skin of the thorax. ”

“ The figure-of-8 and kite-like action of the wing referred to lead us to explain how it happens that the wing, which in many instances is a comparatively small and delicate organ, can yet attack the air with such vigour as to extract from it the recoil necessary to elevate and propel the flying creature. ”

“ The Wing during its Vibration produces a Cross Pulsation.—The oscillation of the wing on two separate axes—the one running parallel with the body of the bird, the other at right angles to it (fig. 80, a b, c d) —is well worthy of attention, as showing that the wing attacks the air, on which it operates in every direction, and at almost the same moment, viz. from within outwards, and from above downwards, during the down stroke ”

“ The wing is supplied with vertical springs, which assist in slowing and reversing it towards the end of the down and up strokes, and these, in conjunction with the elastic properties of the wing itself, contribute powerfully to its continued play. ”

“ But in humming-birds and swifts, the lower part of the wing is the longer.
In some birds, the wing, when spread out, is much longer than all the body. The wing folds up, something like a crab’s claw, or as you would shut a knife. In birds that are walkers, and not flyers, the first wing-bone is short. The penguin, which never flies, has a little short wing, which looks like a hand, without any arm. ”

“ The wing is not one surface but a series of narrow surfaces lapping in such a manner that they unite to form one broad surface when the downward stroke is made, and with the upward stroke are separated so that the air passes between them. Greater power in the downward stroke and less resistance in the upward stroke are also secured by the curvature of the wing. ”

“ THE WING STRUCTURE.—The wing structure of every flying creature that man has examined, has one universal point of similarity, and that is the manner of its connection with the body. It is a sort of universal joint, which permits the wing to swing up and down, perform a gyratory movement while doing so, and folds to the rear when at rest. ”

“ The wings of the bird, if flying, are only visible as a thin grey film, bounded above and below by fine black threads, in form of a St Andrew’s cross,—the effect on the observer’s retina of the instantaneous reversal of the motion of the wing at each beat—the strokes being so rapid as to leave no more distinct image. ”

“ A short and rounded wing, on the other hand, always accompanies a more feeble or more laborious flight, and one much less under command. We might suppose, therefore, that the butterflies which possess this peculiar form were better able to escape pursuit. ”