. Animal flight; a record of observation . ure ofthe air. A little consider-B — ation will show that in fast flex-gliding the pressure isexerted at right angles tothe surface of the wing, asc /T^~r^ is tne case m sl°w flex- Fig. 67. gliding. Diagram of bird showing position of pull and drag, at Ain slow Hex-gliding, and at C in fast flex-gliding. At B is shownan imaginary case in which the wings are placed in the fast flex-gliding position, except that they are not advanced. Hence betweenthe pull and the drag there is a couple tending to rotatethe bird round its transverse axis. In fig. 67, th
. Animal flight; a record of observation . ure ofthe air. A little consider-B — ation will show that in fast flex-gliding the pressure isexerted at right angles tothe surface of the wing, asc /T^~r^ is tne case m sl°w flex- Fig. 67. gliding. Diagram of bird showing position of pull and drag, at Ain slow Hex-gliding, and at C in fast flex-gliding. At B is shownan imaginary case in which the wings are placed in the fast flex-gliding position, except that they are not advanced. Hence betweenthe pull and the drag there is a couple tending to rotatethe bird round its transverse axis. In fig. 67, the disposition of the wing in slow flex-gliding is shown at A. The arrows represent the positionand direction of the total pull and total position of affairs in fast flex-gliding is shownat C. The weight is as before. The resistance topassage through the air is increased owing to theincreased speed. Therefore the total drag mustact in a more backward direction. Hence I have drawnthe total drag arrow in C pointing more backwards. 200 ANIMAL FLIGHT.
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