DR PETTIGEEW ON" THE PHYSIOLOGY OF WINGS. 



421 



gressive movement, i.e., a horizontal rather than a vertical movement, Thus, if 

 the anterior or thick margin of the wing be directed upwards, and the angle 

 which the under surface of the wing makes with the horizon be something like 



a 



Fig. 59. t 



Fig. G0.§ 



45°, the wing will, when made to vibrate by the hand, fly with an undulating- 

 motion in an upward direction, like a pigeon to its dovecot. If the under sur- 

 face of the wing makes no angle, or a very small angle, with the horizon, it will 



* Fig. 57 represents a longitudinal section of bamboo reed 10 feet long, and 1 inch wide. 



+ Fig. 58. The appearance presented by the same reed when made to vibrate by the hand. The reed vibrates on 

 either side of a given line (x x), and appears as if in two places at the same time, viz., c and /, g and d, e and h. It is 

 thus during its vibration thrown into figures of 8 or opposite curves. 



t Fig. 59. The appearance presented by the same reed when made to vibrate more rapidly. In this case the waves 

 made by the reed are less in size, but more numerous than in fig. 58. The reed vibrates alternately on either side of the 

 line x x, being now at i now at m, now at n now aty, now at k now at o, now at p now at I. This reed, when made to 

 vibrate by the hand, has no dead points, a circumstance due to the fact that no two parts of it reverse or change their 

 curves at precisely the same instant. It is because of this curious reciprocating motion that the wing can seize and dis- 

 engage itself from the air with such rapidity. 



§ Fig. 60. The same reed with a flexible elastic curtain or fringe added to it. The curtain consists of tapering 

 whalebone rods covered with a thin layer of india-rubber, a b anterior margin of wing, c d posterior ditto. 



|[ Fig. 61 gives the appearance presented by the artificial wing (fig. 60) when made to vibrate by the hand. It is 

 thrown into longitudinal and transverse waves. The longitudinal waves are represented by the arrows c d e, and the 

 transverse by the arrows f g h. A wing constructed on this principle gives a continuous elevating and propelling power. 

 It developes figure of 8 curves during its action in longitudinal, transverse, and oblique directions. It literally floats upon 

 the air. It has no dead points — is vibrated with amazingly little power, and has apparently no slip. It can fly in an 

 upward, downward, or horizontal direction by merely altering its angle of inclination to the horizon. It must be 

 applied to the air by an irregular motion — the movement being most sudden and vigorous always at the beginning of 

 the down stroke. 



