426 



DR PETTIGKEW ON THE PHYSIOLOGY OF WINGS. 



subordinate reeds never permitting its posterior or free margin to rise above its 

 anterior or fixed margin. The under surface of the wing consequently descended 

 so as to present a flat surface to the earth. It experienced much resistance 

 from the air during the down stroke, the amount of buoyancy thus furnished being 

 very considerable. The above form of wing is more effective during the down 

 stroke than during the up. It, however, elevates and propels during both, the 

 forward travel being greatest during the down stroke. 



Compound Wave Wing. — In order to render the movements of the wing as 

 simple as possible, I was induced to devise a form of pinion, which for the sake 

 of distinction I shall designate the Compound Wave Wing. This wing consists 

 of two wave wings united at their roots, as represented at b, c, (A, A') of fig. 

 66. It is attached by its centre to the head of the piston by a compound joint 



Fig. 66. 



(x), which enables it to move in a circle, and to rotate along its anterior margin 

 [a, b, c, d, A, A') in the direction of its length. The circular motion is for steer- 

 ing purposes only. The wing rises and falls with every stroke of the piston, 

 and the movements of the piston are quickened during the down stroke, and 

 slowed during the up one (vide note to fig. 63, p. 424, also pp. 432 and 433). 



During the up stroke of the piston the wing is very decidedly convex on its 

 upper surface (a, b, c, d, A, A'), its under surface being deeply concave and inclined 

 obliquely upwards and forwards. It thus evades the air during the up stroke. 



