The problem is not an unphilosophical phantom, but a mathematically demonstrated truth, which needs only actual realization to revolutionize the world for the better. That the air is navigable can no longer be denied.
XII.—FUNDAMENTAL PRINCIPLES OF FLIGHT.
In contemplating the boundless atmosphere, we perceive it to be tenanted by a multitude of creatures of varied form and size, who move and direct themselves with marvellous ease and skill. These beings, so different in their nature, form and construction—from the proud eagle to the "blood-thirsty" mosquito—resemble one another in the possession of three important fundamental principles which constitute the power of flight. These are—weight or gravity, surface or resistance of the atmosphere against it, and force or power of projection.
The medium in which the phenomenon of flight is produced—the air—is an invisible, impalpable, comparatively imponderable fluid, and its density is nearly 800 times less than that of water. Hence a movement through it can be made far more rapidly than through its sister medium. Nevertheless, if agitated, it is capable of exerting great pressure, as the tempestuous storms, overturning fences, unroofing houses, uprooting trees, and carrying even large animals into the air, teach us. Hereon then, that is, the proper manipulation principally in creating artificial currents of air, hinges the secret of flight, because this phenomenon is reproduced in a manner identical, if a surface is moved against it, as we see in the wings of flying creatures.
XIII.—WEIGHT.
Weight is absolutely indispensible in flight, it adds momentum and assists the propelling power—with greater force comparatively in heavier bodies. A wooden cannon ball can fly only a fraction of the distance of an iron one; and an equal weight of musket balls, propelled by the same charge of powder, will not reach near so far as the cannon ball, because of its consolidation in one body; and a feather or little toy balloon can not only not be propelled, but will actually recoil if attempted. Hence, all flying animals are many hundred times heavier than air, and the heaviest are generally the best flyers, yet require the least amount of surface and force in proportion.
The sympathy existing between weight and power is very great. Weight acts in flight upon the oblique surfaces of the wings in conjunction with the power expended, and thereby husbanding the latter immensely. Thus only are the denizens of the air enabled to perform long journeys, while otherwise they could retain their position in the upper region but a very brief time, as their strength is no greater than that of other animals and would soon give out. Weight acts on flying creatures in a similar manner as we see it in the clock, where weight is the moving power, and the pendulum merely regulates its movements.
Of course, the belief of many, that birds have large air cells in their interior, that those cavities contain heated air, and that this heated air in some mysterious manner contributes to, if it does not actually produce, flight, falls to the ground upon the least reflection. No argument could be more fallacious. The bird is a heavy, compact, by no means bulky body, and that trifle of heated air, or gas, if such were the case, but is not, which possibly might help elevation, would be but dust in the scale. A small balloon of two feet diameter—a larger body than any bird—can lift only about a quarter of a pound. But, besides, many admirable flyers, such as bats, have no air cells; while many animals, never intended to fly, are provided with them. It may, therefore, be reasonably concluded that flight is in no way connected with air cells, and the best proof that can be adduced is to be found in the fact that it can be performed to perfection in their absence.