But birds do fly, notwithstanding this wonderful array of contradictory exhibitions. Observation has not enabled us to learn why these things are so. High authorities, and men who are expert aviators, tell us that the bird flies because it is able to pick out ascending air currents.
THEORIES ABOUT FLIGHT OF BIRDS.—Then we are offered the theory that the bird has an instinct which tells it just how to balance in the air when its wings are once set in motion. Frequently, what is taken for instinct, is something entirely different.
It has been assumed, for instance, that a cyclist making a turn at a rapid speed, and a bird flying around a circle will throw the upper part of the body inwardly to counteract the centrifugal force which tends to throw it outwardly.
Experiments with the monorail car, which is equipped with a gyroscope to hold it in a vertical position, show that when the car approaches a curve the car will lean inwardly, exactly the same as a bird, or a cyclist, and when a straight stretch is reached, it will again straighten up.
INSTINCT.—Now, either the car, so equipped possesses instinct, or there must be a principle in the laws of nature which produces the similarity of action.
In like manner there must be some principle that is entirely independent of the form of matter, or its arrangement, which enables the bird to perform its evolutions. We are led to believe from all the foregoing considerations that it is the manner or the form of the motion.
MODE OF MOTION.—In this respect it seems to be comparable in every respect to the great and universal law of the motions in the universe. Thus, light, heat and electricity are the same, the manifestations being unlike only because they have different modes of motion.
Everything in nature manifests itself by motion. It is the only way in which nature acts. Every transformation from one thing to another, is by way of a movement which is characteristic in itself.
Why, then, should this great mystery of nature, act unlike the other portions of which it is a part?
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.