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birds, all which goes to prove that sound is a concomitant of rapidly vibrating wings.
The Wing area Variable and in Excess.—The travellingsurfaces of insects, bats, and birds greatly exceed those of fishes and swimming animals; the travelling-surfaces of swimming animals being greatly in excess of those of animals which walk and run. The wing area of insects, bats, and birds varies very considerably, flight being possible within a com
Fig. 57.—Shows a butterfly with comparatively very large wings. The nervures are seen to great advantage in this specimen : and the enormous expanse of the pinions readily explains the irregular flight of the insect on the principle of recoil, a Anterior wing, b Posterior wing, e Anterior'margin of wing. /Ditto posterior margin, g Ditto outer margin. Compare with beetle, fig. 58.—Original.
paratively wide range. Thus there are light-bodied and largewinged insects and birds—as the butterfly (fig. 57) and heron (fig. 60, p. 126); and others whose bodies are comparatively heavy, while their wings are insignificantly small—as the sphinx moth and Goliath beetle (fig. 58) among insects, and the grebe, quail, and partridge (fig. 59, p. 126) among birds. The apparent inconsistencies in the dimensions of the body and wings are readily explained bythe greater muscular development of the heavy-bodied short-winged insects and birds, and the increased power and rapidity with which the wings in them are made to oscillate. In large-winged animals the movements are slow; in small-winged ones comparatively very rapid. This shows that flight may be attained by a heavy, powerful animal with comparatively small wings, as well as by a lighter one with enormously enlarged wings. While there is apparently no fixed relation between the area of the wings and the animal to be raised, there is, unless in the case of sailing birds,1 an unvarying relation between the weight of
Fig. 58. —Under-surface of large beetle (Goliathus micans), with deeply cdncave and comparatively small wings (compare with butterfly, fig. 57), shows that the nervures (r, d, e, /, n, %, n) of the wings of the beetle are arranged along the anterior margins and throughout the substance of the wings generally, very much as the bones of the arm, forearm, and hand, are in the wings of the bat, to which they bear a very marked resemblance, both in their shape and mode of action. The wings are folded upon themselves at the point e during repose. Compare letters of this figure with similar letters of fig. 17, p. 36.—Original.
the animal, the area of its wings, and the number of oscillations made by them in a given time. The problem of flight thus resolves itself into one of weight, power, velocity, and small surfaces; versus buoyancy, debility, diminished speed, and extensive surfaces,—weight in either case being a sine gud non. In order to utilize the air as a means of transit, the body in motion, whether it moves in virtue of the life it possesses, or because of a force superadded, must be heavier
1 In birds which skim, sail, or glide, the pinion is greatly elongated or rihbon-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. This is especially the case when it is proceeding against a slight breeze—the wind and the inclined planes resulting from the upward inclination of the wings reacting upon each other, with this very remarkable result, that the mass of the bird moves steadily forwards in a more or less horizontal direction.
Fig. 59.—The Red-legged Partridge (Perdix rubra) with wings fully extended as in rapid flight, shows deeply concave form of the wings, how the primary and secondary feathers overlap and support each other during extension, and how the anterior or thick margins of the wings are directed upwards and forwards, and the posterior or thin ones downwards and backwards. The wings in the partridge are wielded with immense velocity and power. This is necessary because of their small size as compared with the great dimensions and weight of the body.
If a horizontal line be drawn across the feet [a, e) to represent the horizon, and another from the tip of the tail (a) to the root of the wing (d), the angle at which the wing strikes the air is given. The body and wings when taken together form a kite. The wings in the partridge are rounded and broad. Compare with heron, fig. 60.—Original.
than the air. It must tread and rise upon the air as a swimmer upon the water, or as a kite upon the wind. It must act against gravity, and elevate and carry itself forward at the expense of the air, and by virtue of the force which
Fig. 00.— The Grey Heron (Ardea cinerea\ in full flight. In the heron the wings are deeply concave, and unusually large as compared with the size of the bird. The result is that the wings are moved very leisurely, with a slow, heavy, and almost solemn beat.. The heron figured weighed under 3 lbs.; and the expanse of wing was considerably greater than that of a wild goose which weighed over 9, lbs. Flight is consequently more a question of power and weight than of buoyancy and surface. d, e,fAnterior thick strong margin of right wing, c, a, b Posterior thin flexible margin, composed of primary ('«), secondary (a), and tertiary (c) feathers. Compare with partridge, fig. 59.—Original.
resides in it. If it were rescued from the law of gravity on the one hand, and bereft of independent movement on the other, it would float about uncontrolled and uncontrollable, as happens in the ordinary gas-balloon.
That no fixed relation exists between the area of the wings and the size and weight of the body, is evident on comparing the dimensions of the wings and bodies of the several orders of insects, bats, and birds. If such comparison be made, it will be found that the pinions in some instances diminish while the bodies increase, and the converse. No practical good can therefore accrue to aerostation from elaborate measurements of the wings and trunks of any flying thing; neither can any rule be laid down as to the extent of surface required for sustaining a given weight in the air. The wing area is, as a rule, considerably in excess of what is actually required for the purposes of flight. This is proved in two ways. First, by the fact that bats can carry their young without inconvenience, and birds elevate surprising quantities of fish, game, carrion, etc. I had in my possession at one time a tame barn-door owl which could lift a piece of meat a quarter of its own weight, after fasting four-and-twenty hours; and an eagle, as is well known, can carry a moderatesized lamb with facility.
The excess of wing area is proved, secondly, by the fact that a large proportion of the wings of most volant animals may be removed without destroying the power of flight. I instituted a series of experiments on the wings of the fly, dragon-fly, butterfly, sparrow, etc., with a view to determining this point in 1867. The following are the results obtained:—
Blue-bottle Fly.—Experiment 1. Detached posterior or thin half of each wing in its long axis. Flight perfect.
Exp. 2. Detached posterior two-thirds of either wing in its long axis. Flight still perfect. I confess I was not prepared for this result.
Exp. 3. Detached one-third of anterior or thick margin of either pinion obliquely. Flight imperfect.
Exp. 4. Detached one-half of anterior or thick margin of either pinion obliquely. The power of flight completely destroyed. From experiments 3 and 4 it would seem that the anterior margin of the wing, which contains the principal nervures, and which is the most rigid portion of the pinion, cannot be mutilated with impunity.
Exp. 5. Removed- one-third from the extremity of either wing transversely, i.e. in the direction of the short axis of the pinion. Flight perfect.
Exp. 6. Removed one-half from either wing transversely, as in experiment 5. Flight very slightly (if at all) impaired.
Exp. 7. Divided either pinion in the direction of its long axis into three equal parts, the anterior nervures being contained in the anterior portion. Flight perfect.
Exp. 8. Notched two-thirds of either pinion obliquely from behind. Flight perfect.
Exp. 9. Notched anterior third of either pinion transversely. The power of flight destroyed. Here, as in experiment 4, the mutilation of the anterior margin was followed by loss of function.
Exp. 10. Detached posterior two-thirds of right wing in its long axis, the left wing being untouched. Flight perfect. I expected that this experiment would result in loss of balancing-power; but this was not the case.
Exp. 11. Detached half of right wing transversely, the left one being normal. The insect flew irregularly, and. came to the ground about a yard from where I stood. I seized it and detached the corresponding half of the left wing, after which it flew away, as in experiment 6.
Dragon-Fly.—Exp. 12. In the dragon-fly either the first or second pair of wings may be removed without destroying the power of flight. The insect generally flies most steadily when the posterior pair of wings are detached, as it can balance better; but in either case flight is perfect, and in no degree laboured.
Exp. 13. Removed one-third from the posterior margin of the first and second pairs of wings. Flight in no wise impaired.
If more than a third of each whig is cut away from the posterior or thin margin, the insect can still fly, but with effort.
Experiment 13 shows that the posterior or thin flexible margins of the wings may be dispensed with in flight. They are more especially engaged in propelling. Compare with experiments 1 and 2.
Exp. 14. The extremities or tips of the first and second pair of wings may be detached to the extent of one-third,