. The structure and life of birds. Birds; Evolution. l8o THE STRUCTURE AND LIFE OF BIRDS CHAP. perhaps, would be the only advantage. But it is quite possible to propel a boat in this way, and such a system of rowing would illustrate what takes place in flight. True, the blades of a bird's "oars" face differently, so that, while they propel him, they at the same time raise or maintain him in the air. But the system of leverage is the same. This diagram is a further Fig. 47. X and Z are rigid rods representing the bird's wings hinged at Y to Y Y' the bird's body ; a b an
. The structure and life of birds. Birds; Evolution. l8o THE STRUCTURE AND LIFE OF BIRDS CHAP. perhaps, would be the only advantage. But it is quite possible to propel a boat in this way, and such a system of rowing would illustrate what takes place in flight. True, the blades of a bird's "oars" face differently, so that, while they propel him, they at the same time raise or maintain him in the air. But the system of leverage is the same. This diagram is a further Fig. 47. X and Z are rigid rods representing the bird's wings hinged at Y to Y Y' the bird's body ; a b and c b are the muscles which lower the wings. "I'he shortening oi ah and c b will cause Y Y' to rise, since the air resists the descent of X and Z. After Alix, Appareil Locomoteur des Oiseanx. Horizontal Flight. Why does a bird advance horizontally when it works its wings up and down .-' The common metaphor which makes them oars is picturesque, but may be, as I have shown, misleading. Vergil, who, in describing Daedalus' wings, uses the expression "Remigium alarum," doubtless never intended to commit himself to any theory of flight. If in a scientific work, wings. 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
