. The structure and life of birds. Birds; Evolution. VII FLIGHT 183 into two forces, one represented by XM, the other by XR. But the force XR will have little effect since the water offers great resistance to the movement of a boat sideways through it; at any rate if it has a keel or a centreboard. The force XM will cause the boat to move in the direction she is meant to go. This is an excellent illustration of what happens in the flight of a bird. When the wing is descending its front margin is lower than its hind margin ; it is turned so that the long feathers slope upwards. For simplicity.
. The structure and life of birds. Birds; Evolution. VII FLIGHT 183 into two forces, one represented by XM, the other by XR. But the force XR will have little effect since the water offers great resistance to the movement of a boat sideways through it; at any rate if it has a keel or a centreboard. The force XM will cause the boat to move in the direction she is meant to go. This is an excellent illustration of what happens in the flight of a bird. When the wing is descending its front margin is lower than its hind margin ; it is turned so that the long feathers slope upwards. For simplicity. Fig so. X Y ^ section of wing ; X, front margin ; Y, hind margin ; W = wind caused by the down stroke ; BA, resultant force, which is resolved into BC, BD. we must imagine that the air is quite still. The wing descends with great velocity through it, " making its own wind " like a bicyclist. The resistance of the air will be equal to a wind blowing vertically upward (W in Fig. 50). When it strikes the inclined surface of the wing its force will act in a direction at right angles to it (BA). The force BA may be divided into two forces, BD, which supports the bird, BC, which drives him onward. Whether Professor Pettigrew's description of the wing's movement agrees with the account I have. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Headley, F. W. (Frederick Webb), 1856-1919. London, New York, Macmillan
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbirds, bookyear1895
