. A dictionary of birds . ord Rayleigh On the Resistanceof Fluids, Philos. Mag. ser. 5, ii. p. 430 (1876). FLIGHT 26s for the same reason as a sheet of paper which is allowed to falltends to describe curves with their concavities upwards, so alsodoes a gliding bird tend to rise in the air whenever its velocity isincreased. This tendency the bird can counteract in various can, in the first place, change the position of its centre ofgravity forwards in relation to the position of its centre of supportby the outstretched wings. It can do this in the case of such abird as a Heron by extend
. A dictionary of birds . ord Rayleigh On the Resistanceof Fluids, Philos. Mag. ser. 5, ii. p. 430 (1876). FLIGHT 26s for the same reason as a sheet of paper which is allowed to falltends to describe curves with their concavities upwards, so alsodoes a gliding bird tend to rise in the air whenever its velocity isincreased. This tendency the bird can counteract in various can, in the first place, change the position of its centre ofgravity forwards in relation to the position of its centre of supportby the outstretched wings. It can do this in the case of such abird as a Heron by extending its neck, which is usually bent Aviththe head retracted, biit which, Avhen the bird strives to fly fast, isstretched out forward to the full extent. In the case of mostbirds, however, the short neck does not allow of this means ofmoving forward or backward of the centre of gravity, and what thebird does is to move forward or backward the extended a matter of fact, it had been noted long before the true reason. Fig. 3. (From Marey.) was understood that birds which glide slowly (Fig. 3) had theirwings much further forward than the partially flexed wings ofbirds which gliderapidly (Fig. 4)through the air.^ A similar effect isobtained by spread-ing out the tail-feathers, whichmoves back the cen-tre of the plane ofsuspension formedby the wings, body,and tail, therebyrelatively advancing the centre of gravity of the bird. Changeof direction, upward or downward, can in this way be obtained ^ This fact (that the point of maximum resistance is moved forward when aflat surface strikes a fluid, with at the same time a movement parallel with theplane of the surface) seems to us well fitted to explain why it is that the shafts ofthe primary wing-feathers, which during extension of the wing make a great angle
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Keywords: ., bookauthorlyde, bookcentury1800, bookdecade1890, booksubjectbirds
