. British birds. Birds. F. W. HE ABLE Y : WIND AND FLIGHT. 117 The principle is the same when the wing- beats the air, and when the bird gliding- with outspread wings inclines his body slig-htly upward, so that the air may act on his whole outspread surface. The accompanying photograph (Fig. 1) shows the position of the wing at important phases of the stroke. Gliding. Gliding introduces us to another wonderful fact in the action of air in motion. We can understand this best by considering what hapj)ens when a boat is tacking, sailing- close to the wind, so that the air impinges on the sail at
. British birds. Birds. F. W. HE ABLE Y : WIND AND FLIGHT. 117 The principle is the same when the wing- beats the air, and when the bird gliding- with outspread wings inclines his body slig-htly upward, so that the air may act on his whole outspread surface. The accompanying photograph (Fig. 1) shows the position of the wing at important phases of the stroke. Gliding. Gliding introduces us to another wonderful fact in the action of air in motion. We can understand this best by considering what hapj)ens when a boat is tacking, sailing- close to the wind, so that the air impinges on the sail at an acute angle. It strikes against the foremost part of the sail, and, being- prevented from continuing in its natural coiu-se, rushes along the sail—as shown by the arrows in the diagram—and thus, if the sail is a broad w w. Fig. 2.—Diagram illustrating Gliding. s l, sail; w, wind. one, its front margin does all the work. To apply this to gliding flight—it is the front margins of the wings that support the bird when he holds them outstretched, inclined only slightly to the horizontal. Consequently, the greater the extent of the front margin, the better able will he be to maintain his level or even to ascend. If he wishes to descend as he glides, he will partly flex his 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 London, Witherby & Co
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Keywords: ., bookcentury1900, bookdecade1900, bookpublisherl, booksubjectbirds
