In the monoplane each wing would project out about three feet more on each side, but it would have eight and a half feet fore and aft spread to the biplane's five feet, and thus act as a greater support. THE ORTHOPTER.--The term orthopter, or ornithopter, meaning bird wing, is applied to such flying machines as depend on wing motion to support them in the air. Unquestionably, a support can be obtained by beating on the air but to do so it is necessary to adopt the principle employed by nature to secure an upward propulsion. As pointed out elsewhere, it cannot be the concaved type of wing, or its shape, or relative size to the weight it must carry. As nature has furnished such a variety of data on these points, all varying to such a remarkable degree, we must look elsewhere to find the secret. Only one other direction offers any opportunity, and that is in the individual wing movement. NATURE'S TYPE NOT UNIFORM.--When this is examined, the same obscurity surrounds the issue. Even the speeds vary to such an extent that when it is tried to differentiate them, in comparison with form, shape, and construction, the experimenter finds himself wrapt in doubt and perplexity. 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.