XIII.—WEIGHT.
Reading edition
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.