THEORY OF INSECT FLIGHT 



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however, than in the process of sculling, since " the flexible mem- 

 brane which constitutes the anterior part of the wing presents a 

 rigid border, which enables the wing to incline itself at the most 

 favorable angle." 



" The muscles only maintain the 

 to-and-fro movement, the resist- 

 ance of the air does the rest, 

 namely, effects those changes in 

 surface obliquity which determine 

 the formation of an 8-shaped tra- 

 jectory by the extremity of the 

 wing." 



Lendenfeld has applied photography 

 to determine the position of the wings 

 of a dragon-fly, and Marey has carried 

 chronophotography farther to indicate 

 the normal trajectory of the wing, and 

 to show the position in flight. Fig. 

 166 shows a bee in various phases of 

 flight. " The insect sometimes assumes 

 almost a horizontal position, in which 

 case the lower part of its body is much 

 nearer the object-glass than is its head, 

 and yet both extremities are equally 

 well denned in the photograph. The 

 successive images are separated by an 

 interval of ^ of a second (a long time 

 when compared to the total time occu- 

 pied by a complete wing movement, 

 i.e. T ^ of a second). And hence it is 

 useless to attempt to gain a knowl- 

 edge of the successive phases of move- 

 ment by examining the successive 

 photographs of a consecutive series rep- 

 resenting an insect in flight. Never- 

 theless an examination of isolated 

 images affords information of extreme 

 interest with regard to the mechanism 

 of flight. 



"We have seen that owing to the 

 resistance of the air the expanse of wing 

 is distorted in various directions by 

 atmospheric resistance. Now, as the 

 oscillations during flight are executed in 

 a horizontal plane, the obliquity of the 

 wing-surface ought to diminish the 

 apparent breadth of the wing. This appearance can be seen in Fig. 167. There 

 is here a comparison between two Tipulae : the one in the act of flight, the 

 other perfectly motionless and resting against the glass window. 



"The motionless insect maintains its wings in a position of vertical exten- 



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