244 MOVEMENT 



According to our view, on the contrary, the extremity 

 of the wing describes each limb of the lemniscate in 

 succession, in a dual motion from left to right, and 

 then from right to left. Meanwhile the surface of the 

 wing is variously distorted by the resistance of the 

 air. In Fig. 172 dotted lines indicate the direction 

 of this distortion which could never amount to a com- 

 plete reversal. Now, 

 the mechanical theory 

 which can be deduced 

 .rom this optical figure 

 depends entirely on the 

 manner in which the 

 wing is supposed to 



Fig. 172.— Trajectory of the anterior order of , " , «i T • 



tbe wing during a complete oscillation liave deSCl'lbed it. Ac- 

 (Marey). The small lines which are set -. . -..- ^ . 



obliquely in various directions represent the COrCling tO IVll*. X ettl- 



inclinations of the surface of the wing. , , i .-, 



grew s theory, the revo- 

 lution of the wing is active and due to the contraction 

 of muscles. According to our theory, the change in 

 inclination of the wing is passive and brought about by 

 the resistance of the air, for it is only the posterior 

 part of the wing that is distorted, the anterior part 

 being kept straight and stiff by a rigid nervure. The 

 importance of a correct interpretation of the figure 

 described by an insect's wing is very great, because the 

 explanation of the mechanism of flight depends upon 

 it. We have, however, no desire to weigh the respective 

 merits of the two theories, we only wish to enumerate 

 the experiments by which we have demonstrated our 

 own views. 



Experiments for determining the Direction taken by 

 the Wing in course of Movement, and Explanation of the 

 Mechanism by which the Alteration in Inclination is 

 effected. — The optical method, namely, that of deter- 

 mining the movements of the wing by the impression 

 left on our organs of sight by the gold spangle fastened 



