Now, facts prove that man can, without danger, descend from an high elevation under a surface of much less than fifteen feet diameter; and the force to lift himself, as will be shown hereafter, is also comparatively small. He can walk up stairs, and likewise mount upon air, which, properly manipulated, becomes sufficiently solid.
It has been demonstrated beyond a doubt, that the heaviest flying animals require the smallest amount of surface and power in proportion. The surface is less, because the resistance of the atmosphere is much greater toward one unbroken body than all the parts thereof if detached. Hence a stork, weighing eight times as much as a pigeon, needs only five square feet of surface, while the eight pigeons, with nearly one square foot each, possess together over seven square feet; and the common fly, if magnified to the size of the crane, would show a surface sixty times as large.
The heaviest flyers require the least amount of power, because weight, as stated before, itself is power, which increases in a certain ratio. Hence we find the muscular force of the smaller beings, who possess little weight, to be enormous; this is particularly so with insects, who are the strongest in creation. A stag-beetle, of which two hundred weigh only one pound, can lift fourteen ounces; crickets leap eighty times their own length, and the "lively flea" can jump through space estimated at even two hundred times the length of its body—which accounts for the difficulty of catching it. If a mouse would simply reproduce the gait of a horse, its progress would be about twenty inches per minute only, and cats would soon find themselves out of employment.
Nature has wisely established a compensation to make amends for the diminutiveness of organs by rapidity of movement, and has, consequently, furnished the animal with the necessary power to produce this rapidity.
The force necessary for lifting in all winged beings is not near so great as is generally supposed. The fall of a body, continually accelerating, is seventeen feet per second, and a very great force would be necessary indeed to offset this gravitation, if that second were allowed to expire without a counter-movement; but when that body is provided with a parachute-like arrangement, there is no such rapid fall of seventeen feet per second; and when, besides, the force is applied constantly, thereby counteracting even a fraction of the fall, the power needed to accomplish this is but a trifle; it is the principle, to use a homely phrase, that "a stitch in time saves nine." What extra strength the animal possesses has to be used in pursuit or escape, from the powerful eagle to the minutest insect; they must be prepared to exert at a given moment all the strength that nature has given to them in store.
Their strength is no greater than that of fishes or quadrupeds; all possess surplus power greatly above the need of their average use, and the strength exhibited therefore by flying creatures shows only that but a small portion of it is used for lifting and propelling purposes.
Eagles have been known to carry off small deer, lambs, hares, and even young children. Many of the fishing birds, as pelicans and herons, can likewise carry considerable loads, while the smaller birds are capable of transporting comparatively large twigs for building purposes. A swallow can traverse 1000 miles at a single journey, and the swift, the fastest of all, is known to have made nearly 180 miles an hour. The albatross, despising compass and land-mark, trusts himself boldly for weeks together to the mercy or fury of the mighty ocean; and the huge condor of the Andes, as Humboldt, Darwin, Orton, and others inform us, lifts himself to a hight where no sound is heard, and from an unseen point surveys, in solitary grandeur, the wide range of plain and mountain below. He has been seen flying over the Chimborazo, and attains, on occasions, an altitude of six miles.
XVI.—FLYING CREATURES, THEIR PROPORTIONS, MOVEMENTS.
The great common characteristic of the different winged beings are the same throughout all the modifications of detail. These are, as stated, weight, extension of surface, and the mechanical application of the propelling force; so that the animal is a gliding plane, part of which is fixed and the other moveable, and the whole being maintained in stable equilibrium by the weight of the body, placed a little below the plane of suspension.